THE FRUIT OF OPUNTIA FULGIDA 
 
 A STUDY OF 
 PERENNATION AND PROLIFERATION IN 
 THE FRUITS OF CERTAIN CACTACE/E 
 
 BY 
 DUNCAN S. JOHNSON 
 
 QK4-95 
 
 Cll 
 
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 PUBUSHED BY THE CaRNEGIE INSTITUTION OF WASHINGTON 
 WASHINGTON. 1918 
 
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 ATE UNIVERSITY I IBRARIES 
 
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 S00555181 P 
 
Worth Carolina 
 
 ibrary 
 
 THE FRUIT OF OPUNTIA FULGIDA 
 
 A STUDY OF 
 PERENNATION AND PROLIFERATION IN 
 THE FRUITS OF CERTAIN CACTACE/E 
 
 BY 
 DUNCAN S: JOHNSON 
 
 PUBUSHED BY THE CaRNEGIE InSTITLT 
 WASHINGTON. V. 
 
 THIS BOOK IS DUE ON THE DATE 
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 CAENEGIE INSTITUTION OF WASHINGTON 
 Publication Xo. 2G9 
 
 BALTIMORE, MD., U. 8. A, 
 
CONTENTS. 
 
 PAGE 
 
 Comparison of the fruit of Opuntia fulgida with those of other angiosperms. . 5 
 
 Vegetative structure of Opuntia fulgida 8 
 
 Reproductive organs of Opuntia fulgida 9 
 
 Origin and structure of the flovi^er 9 
 
 Development of the wall of the ovary with its tubercles 9 
 
 Structure and fate of the leaves of the ovarian wall 10 
 
 Areoles or axillary buds of the ovarian wall 11 
 
 Number, size and distribution of the areoles 12 
 
 Origin of the growing point of the areole and sequence of initia- 
 tion of its organs 12 
 
 The trichomes of the areole 13 
 
 The nectaries of the areole, their distribution and morphology. ... 14 
 Spines or thorns of the areole, their distribution, structure, and 
 
 fate 15 
 
 Bristles or spicules of the areole, their number, structure, and 
 
 fate 16 
 
 The perianth, stamens, style, and stigmas, their development and 
 
 abscission 17 
 
 Morphology of the ovary 20 
 
 The fruit: Its structure, persistence, and fate, normal and abnormal. ... 25 
 
 The fruit at the time of abscission of the perianth 25 
 
 The mature fruit 27 
 
 The perennating fruit: Its structure and secondary growth 29 
 
 The seed : Its structure, persistence, and germination 32 
 
 Proliferation of flower and fruit 35 
 
 Proliferation from attached flower buds 35 
 
 Proliferation of persistent attached fruits 37 
 
 Proliferation of fallen fruits 38 
 
 Causes and significance of perennation and of the diverse types of 
 
 proliferation 41 
 
 Proliferation of flower or fruit in allied species 47 
 
 Proliferation of joints and fruits in relation to the sterility of fruits 51 
 
 Summary and conclusions 53 
 
 Literature cited ..._• 56 
 
 Explanation of plates % 57 
 
FRONTISPIECE 
 
 A mature plant of Opuntia fukjuhi on reservntion of Desert Laboratory at Tucson, showing 
 a frequent type of forked trunk, due to injury of main axis, also the branching habit 
 and clusters of fruit. The nesting bird is the cactus wren, Heleodytes hrunneicapillm 
 couesi (Sharpe). 
 
THE FRUIT OF OPUNTIA FULGIDA. 
 
 A STUDY OF PERENNATION AND PROLIFERATION 
 IN THE FRUITS OF CERTAIN CACTACE/E.' 
 
 By DUNCAN S. JOHNSON. 
 
 This paper embodies a discussion of the occurrence and significance of a 
 number of striking peculiarities in the development and fate of the per- 
 sistent, self-propagating fruits of certain opuntias. The discussion will be 
 concerned primarily with the perennation and vegetative propagation of the 
 ovary of Opuntia fulgida. This cactus has been chosen for special consid- 
 eration because of its most remarkable power of budding off secondary 
 flowers from the primary ones and also of fonning new flowers and vegeta- 
 tive shoots from the long-persistent fruits. 
 
 This investigation has been aided by grants from the Department of 
 Botanical Research of the Carnegie Institution of Washington. Acknowl- 
 edgment is here made to Director D. T. MacDougal for making available 
 to the writer the facilities of the Desert Laboratory at Tucson, Arizona, and 
 of the Coastal Laboratory at Carmel, California. The principal parts of 
 the work have been done at these two laboratories. Other portions ol it 
 and much of the writing of this paper have been done at the Harps-vN-ell 
 Laboratory, at South Harpswell, Maine, and at Johns Hopkins University. 
 Acknowledgment is also made, for aid in securing material, information, or 
 photographs for this study, to Drs. Forrest Shreve and Hermann Spoehr, of 
 tlie Department of Botanical Research of the Carnegie Institution, to Dr. 
 David Griffiths, of the Bureau of Plant Industry, United States Department 
 of Agi-iculture, to Dr. J. 'N. Rose, of the Smithsonian Institution, and to Dr. 
 N. L. Britton, of the INTew York Botanical Garden. 
 
 COMPARISON OF THE FRUIT OF OPUNTIA FULGIDA 
 WITH THOSE OF OTHER ANGIOSPERMS. 
 
 One of the almost universal characteristics of the fruit in augiosperms is 
 the comparative brevity of its development. The whole duration of this, 
 from the inception of the flower to the ripening of the fniit and it^ fiual 
 separation from the pareut plant, or its opening for the discharge of its 
 seeds, is usually less than a year, often very much less. 
 
 The phases of this developmental cycle of the fruit which can usually be 
 distinguished are: First, a j^eriod of initiation and maturing of the parts 
 of the flower, which opens for pollination at about the time an egg has been 
 
 ' Botanical contribution from The Johns Hoplvins University, No. 56. 
 
 5 
 
6 THE FRUIT OF OPUNTIA FULGIDA. 
 
 formed in the embryo sac; secondly, there follows soon after pollination, 
 which is usually succeeded by fertilization, a period of active vegetative 
 growth of the ovary and often of other parts which are to enter into the 
 make-up of the fruit. While the fruit is thus growing to its mature size 
 the seeds are also taking on their characteristic form and size. Thirdly, 
 accompanying or immediately succeeding the final maturing of the seeds, a 
 process of ripening occurs in the fruit. During this ripening process the 
 outer tissues, the niesocarp and epicarp of the fruit, may soften to form a 
 juicy pulp. In this case the starches, distasteful glueosides, acids, tannins, 
 alkaloids, etc., which are often present in the cells of this pulp in the green 
 fruit, are transformed into the sugars, mild acids, and other tasteful flavors, 
 and often also into brightly colored glueosides that make the fruits attractive 
 to animals. While these changes are taking place in the outer layers of the 
 fruit the inner layer, the endocarp, may harden to form the firm stone that 
 protects the seed when it is eaten by animals. In other types of fruits, as in 
 pods and capsules, the ripening process involves a drying out and hardening 
 of all the tissues of the fruit. 
 
 Ripening of the fruit is usually followed, often very promptly, by ita 
 separation from the plant or by its dehiscence and the discharge of its seeds. 
 Either of these two fates of the fruit involves the more or less immediate 
 death of its tissues, aside from the seeds. In a few fruits, such as that of 
 palms like the coconut or the pomes of the Eosace^e, certain tissues of the 
 fruit may remain alive for some weeks or months after separation from the 
 parent plant. The growth occurring in these cases is, however, compara- 
 tively slight and it does not give rise to new buds or new plants. 
 
 In the cases of certain opuntias, chiefly cylindropuntias, the fruits differ 
 from the usual type characterized above in several very remarkable particu- 
 lars. In the first place the fruits do not ripen with the maturing of the 
 seeds, but continue to grow actively without undergoing the usual softening 
 and change of color and of chemical composition so characteristic of the 
 ripening process of most fleshy fruits. Secondly, the fruits of 0. fulgida 
 are not shed from the plant when the seeds are ripe, but usually remain 
 firmly attached and growing, year after year. Thirdly, these attached 
 fruits (or even the unopened flowers), may, in situ, give rise from their 
 axillary buds to from one to ten secondary flowers and fruits. A few weeks 
 later these secondary flowers may give rise in the same way to tertiary ones 
 and these in turn to quaternary ones. Thus, three or four generations of 
 flowers and fruits may be produced, all in a single blooming season of three 
 or four months. Tourthly, if the fruits become separated from the plant 
 and fall on moist soil^ the same axillary buds which in the attached fruits 
 would form nothing but flowers will, in the fallen fruits, give rise to 
 vegetative shoots and roots and to these only. Finally, the embryos of the 
 ripe seeds, inclosed in the persistent, attached fruits, retain their power of 
 germination for many years. 
 
THE FRUIT OF OPUNTIA FULGIDA. 7 
 
 Certain of the peculiarities above noted in the frnits and seeds of Opuntia 
 are, it is true, found in a few other plants, though in none of which the 
 writer has found record is there such an aggregate of unusual features of 
 development, and certain of these features are unlaiown outside the genus 
 Opuntia. 
 
 The persistent attaclnnent and continued gTo^^i;h of the fruit just noted is, 
 as far as I can learn, recorded for but one other family of angiosperms, the 
 Myrtacea). In the genera Callidemon and Melaleuca, for example, the 
 fniits may persist for 10 or 15 years. In the former, according to Ewart 
 (1907), the fruit opens and discharges the living seeds only when it has been 
 killed by the cutting off of its water-supply. This latter may happen in 
 consequence of severe drought, of the breaking off of the branch bearing it, 
 or from the death of the branch or whole tree from fire or other cause. 
 
 There are, however, three important differences between the behavior of 
 the fruits of this Australian " bottle-brush " tree and those of such opuntias 
 as the " choUa " (0. fulgida). In the first place, the persistent fruit of 
 Callistemon does not possess axillary buds and therefore does not, like 
 Opuntia, give rise to secondary and tertiary flowers and fruits from these. 
 Secondly, the fruits of the bottle-brush tree, though they may open and dis- 
 charge their seeds with the first cutting off of the water-supply, do not them- 
 selves fall from the tree until some time after they are dead ; hence, they can 
 play no part in the vegetative propagation of the species. Thirdly, the 
 seeds of Callistemon are ultimately shed from the fruit to play the most 
 important role in the dissemination of the plant, while the seeds of the fleshy 
 fruits of Opuntia fulgida are, as we have seen, never discharged and appar- 
 ently rarely germinate under natural conditions. 
 
 From this comparison of the opuntias with the only other family of plants 
 having fruits with similar peculiarities, it is clear that these Cactacese have 
 become much more abnormal as regards the behavior of propagative struc- 
 tures than any other family of angiosperms. Moreover, the readiness with 
 which a growing-point destined to give rise to a flower may be induced to 
 form a vegetative shoot (by the mere separation of the fruit bearing it from 
 the parent plant) suggests the possibility of discovering here some of the 
 causes detennining the production from the same meristematic mass, in one 
 case of a reproductive organ or in another of a vegetative shoot. 
 
 With this much of suggestion of the structures and phenomena we are to 
 deal with, we shall now examine more closely into the development and fate 
 of the flower, fruit, and seed of certain opuntias. We shall be concerned 
 primarily with those of Opuntia fulgida, in which these structures have been 
 studied most carefully in Tucson, Carmel, and Baltimore. Incidentally we 
 shall also note the structure and capacity for propagation of the vegetative 
 joints of certain species, in order that we may compare with them the 
 structures and phenomena observed in sprouting fruits. 
 
8 THE FRUIT OF OPUNTIA FULGIDA. 
 
 VEGETATIVE STRUCTURE OF OPUNTIA FULGIDA. 
 
 Opuntia fulgida is a tree-like, Sonoran species of Cylindropmvtia, which 
 commonlj grows to 2 or 3 meters in height and forms a rather irregular flat- 
 topped crown. The older or main branches are horizontal, or ascendant at 
 their bases, but bent do^vn at their tips by the weight of the thick terminal 
 branchlets and often of the large clusters of fruits (fig. 1). The spiny 
 trunk is dark brown in color, woody in texture, and may reach 20 or 25 cm. 
 in diameter. The main branches, which are woody like the trunk, may 
 become 8 or 10 cm. in diameter. The ultimate branches at the end of the 
 first season's growth are often 3 to 5 cm. in diameter and 15 to 25 cm. 
 long. These younger branches taper abruptly at the ends and the lateral 
 surfaces are provided with prominent and somewhat elongated mammillae 
 or tubercles (figs. 4, 5, 9a). Each tubercle, at this time, bears at its upper 
 end from 7 to 12 sheathed spines and the growing-point of a lateral bud 
 (figs. 4, 95). The number of spines in each areole steadily increases with 
 age, and hence a branch 10 years old may bear 50 spines in each areole. 
 The leaf to which the areole is axillary is a small and veiy transient structure 
 which (on falling) leaves only a minute scar, like that to be seen on the 
 fruit (figs. 5, 47). The vascular system of the stem is net-like in arrange- 
 ment, being of the same general type as that described and figured by 
 Ganong (1894, fig. 7). During the first year the bulk of the new joint is 
 made up of the mucilaginous pulp of the pith and cortex. The latter has 
 a well-developed photosynthetic and aerating system of the type to be 
 described in dealing with the fruit, and large numbers of slime-cells {cf. 
 Wetterwald, 1889, fig. 19). Chloroplasts are abundant throughout the 
 whole thickness of the cortex of the stem and may even occur within the 
 zone of woody bundles, as happens in the projecting tubercles. With the 
 increase in thickness of the branch the woody cylinder seems to gTOW in 
 diameter more rapidly than the fleshy cortex. The latter finally becomes 
 stretched and smoothed out and the cortex of the mature stem is compara- 
 tively thin and dry (fig. 2, at base). 
 
 On some plants of this species, as has been noted by Toumey (1895), cer- 
 tain of the new joints may remain relatively short and have less prominent 
 tubercles and fewer spines, becoming thus rather fruit-like in form (fig. 7a). 
 These joints are readily detached and on moist soil may give rise to new 
 plants by proliferation, just as the ordinary vegetative branches of this and 
 many other opuntias may do. 
 
THE FRUIT OF OPUNTIA FULGIDA. 9 
 
 REPRODUCTIVE ORGANS OF OPUNTIA FULGIDA. 
 
 The reproductive structures (flower, fruit, and seed) to which most atten- 
 tion has been paid in this study, will be described in some detail under three 
 captions: (1) the origin and structure of the flower; (2) the fruit, its 
 structure, jxirsistence, and fate, normal and almorraal ; (3) the seed, its 
 structure, persistence, and germination. 
 
 The most aberrant features of the development of these reproductive 
 organs are : the structure of the wall of the submerged ovary, with its numer- 
 ous axillary buds ; the capacity of these buds to initiate secondary flowers, 
 either immediately before the primary ones are open or later, in the same or 
 succeeding seasons ; and finally the ability of these same axillary buds, when 
 the fruit is detached, to form adventitious roots and shoots and thus to 
 initiate new plants. 
 
 ORIGIN AND STRUCTURE OF THE FLOWER. 
 
 The primary flower of the season in Opuntia fulgida arises from one of 
 the upper or more terminal axillary buds or areoles of a last year's vegetative 
 joint or from an areole of a fruit of the first, second, or third year preceding. 
 The number of flowers developed on any one joint or fniit in a single season 
 ranges from 1 to 5 or more (figs. 4, 9a). In the case of the fruits, flowers 
 may be formed from other areoles in succeeding years until as many as 10 
 or 12 flowers and fruits are often found attached to a single pei*sistent fruit 
 (fig. 48). The primary flowers of a season are first evident, in 0. fulgida 
 growing near Tucson, during the latter half of April. Open flowers are 
 rarely seen before the middle of May. The first flowers to appear and to 
 open are those developed on vegetative branches. In early May 1912, the 
 larger flower-buds on vegetative branches of one plant observed were 21 mm. 
 long, while the longest ones on a persistent fruit of the same plant were but 
 7 mm. New flowers continue to open successively all through the summer 
 up to the middle of September. (See Tourney, 1898 ; Lloyd, 1907 ). 
 
 DEVELOPMENT OF THE WALL OF THE OVARY WITH ITS TUBERCLES. 
 
 The very young flower-bud, when firet pushing out of the tuft of trichomes 
 and spicules of the areole, is a rather hemispherical body about 0.3 mm. 
 in diameter. Its dome-like or somewhat conical upper end is fonned by the 
 few earlier of the 15 to 30 or sometimes 40 leaves that are finally developed 
 from the Avail of each ovary (figs. 4, 9a, 47). These leaves, w^hen first 
 fonued, arch over the dome-shaped growing-point (figs. 13, 14). As the 
 flower grows, the earlier leaves are pushed outward by the younger ones 
 arising between them (figs. 17, 22). The axis of the flower becomes elon- 
 gated to 1^/4 times its diameter and its surface becomes very irregrular. 
 Below each leaf and its associated bud the surface of the wall of the ovary 
 protrudes to form a prominent tubercle or mammilla (figs. 14, 16, 20). This 
 tubercle is at first finger-like ; later it projects farthest at its upjier end and 
 
10 THE FRUIT OF OPUNTIA FULGIDA. 
 
 narrows to nothing at its lower end, giving it thus a rather triangular outline 
 in a radial section of the fruit (figs. 4, 17, 28). 
 
 At the time of the opening of the flower these tubercles are from 6 to 10 
 mm. in length, are 4 or 5 mm. wide, and project 2 or 3 mm. at the top. In 
 the younger flower-bud the radial width of the tubercle is greater in propor- 
 tion to its length, longitudinal to the ovary, than is indicated above, while in 
 the mature fruit the projection is much less. In morphological nature, this 
 tubercle of the opuntias, as has been sho\vn by Goebel (1889, p. 79), is the 
 combined product of the growing upward together of the leaf-base and the 
 axillary bud above it. This is clearly indicated by a comparison of different 
 stages in its development (figs. 12, 14, 15, 17). The upper end of the 
 tubercle is somewhat circular in cross-section (figs. 30, 49), and somewhat 
 raised at the margin (figs. 21, 22 ; cf. also, Wetterwald, 1889, fig. 19). At 
 the highest point of the abaxial side of the margin is borne the leaf, while the 
 most depressed central portion of the end of the tubercle is occupied by the 
 flattish growing-point of the axillary bud, which is surrounded by the rudi- 
 ments of trichomes, spicules, and nectaries developed from it (figs, dl), 12, 
 15, 32, 50). It is difficult to see how all the structures above a, at the left of 
 the growing-point in figure 50, can be regarded as parts of a single leaf, as 
 they apparently would have to be if the view of the morphology of the 
 tubercle held by Darbishire (1904, p. 395) were accepted. 
 
 The growing-point of the flower, like that of the vegetative shoot, may be 
 slightly convex in form during the period of the initiation of the wall of the 
 ovary with its tubercles and the leaves borne by them. It may even retain 
 some of this convexity during the initiation of the 16 or more sepals and 
 petals (figs. 12, 13, 14), With the beginning of formation of the stamens 
 and carpels, however, the same growing-point becomes depressed to form a 
 cup narro^^ing in at the upper margin, about which the numerous (250) 
 stamens are initiated. Later still, the margin closes in to form the carpels, 
 which unite above to f oi-m the roof of the ovary, and finally stretch upward to 
 form the style and its 6 stigmas (figs. 15, 16, 17). 
 
 STRUCTURE AND FATE OF THE LEAVES OF THE OVARIAN WALL. 
 
 The leaves of the wall of the ovary are, as noted, about 15 to 40 in number. 
 Each leaf is approximately conical in form, has a slightly flattened base, and 
 is curved inward above to end in a sharply pointed tip (figs. 4, 5, 11, 19, 23, 
 47). The mature leaf of the ovary is only 3 or 4 imn. long and but 1 or 1.5 
 mm. in diameter. It is abruptly constricted at the base to a stalk, which is 
 nearer the ventral side and is barely a third the diameter of the part of the 
 leaf just above (figs, 19, 50). The leaves of the lower third of the ovary 
 do not attain more than half the size mentioned, while those of the upper 
 quarter, which are more or less appressed against the sepals, may be some- 
 what longer and are commonly very much broadened (figs. 23, 47, at right). 
 Before the ovary has reached half the size it attains at the opening of the 
 
THE FRUIT OF OPUNTIA FULGIDA. 11 
 
 flower, the lowermost of tlie 15 to 40 leaves of the ovary have dropped off, 
 many of them withering while mere rudiments, half-grown or less (fig. 20, 
 lower areole). The separation occurs at the constriction mentioned, and by 
 the time the flower is well opened all its leaves outside the calyx have fallen. 
 This separation is apparently not determined by a definite abscission layer. 
 The dropping of the leaf is followed by the shrinking together of the short 
 stump of the leaf-stalk and later by the formation of a protecting scar-tissue 
 of 15 to 20 layers of corky cells (fig. 14). Evidently these leaves of the 
 wall of the ovary, being relatively few, small, and transient, are able, like the 
 similar leaves of the vegetative joint, to play only a very subordinate part in 
 the photosynthetic work of the plant. They are certainly much less impor- 
 tant in this work than the abundant and permanent photosynthetic tissue of 
 the wall itself. 
 
 In correspondence with this relatively unimportant photosynthetic work 
 of the leaf, its internal structure shows little of the characteristic specializa- 
 tion of an efficient starch-making organ (figs. 45, 46). Stomata are few 
 and scattered, on the under side of the leaf only. Instead of the character- 
 istic palisade found in the leaves of most other plants and in the joints and 
 fruits of Opuntia fulgida itself, we find the whole outer region, especially on 
 the dorsal side of this leaf, made up of nearly isodiametric cells, among 
 which are scattered small cells containing calcium oxalate crystals and much 
 larger cells filled with slime or mucilage. The latter are of the type that 
 will be described in more detail when we come to the consideration of the 
 internal structure of the fruit (figs. 45, 46). l^ear the flattened base of the 
 leaf (fig. 45), five vascular bundles are to be seen in its cross-section, but 
 only the middle one of these reaches to the tip of the leaf. The subordinate, 
 lateral bundles are made up chiefly of short, broad, thick-Wtilled elements 
 which are often oriented transversely to the leaf. The principal (median) 
 bundle also includes many of these element-s at its upper end, but has a 
 larger proportion of more elongated tracheal elements in its lower portion 
 (figs. 45, 56). 
 
 AREOLES OR AXILLARY BUDS OF THE OVARY. 
 
 By far the most significant peculiarity in structure of the wall of the ovary 
 in Opuntia fulgida, as compared with other angiosperms, is the presence of 
 the axillary buds or areoles distributed over its surface. There is one of 
 these within the leaf, or its scar, at the top of each tubercle, though the basal 
 ones of each fruit remain very rudimentary and never, as far as discovered, 
 give rise to any structures other than a few small spicules or an occasional 
 adventitious root on fruits fallen to the ground. What makes these axillary 
 buds or areoles of the fruits of prime significance in the life of the plant is 
 the fact that those at least of the upper two-thirds of the fruit remain active 
 and each capable of giving rise, on the attached fruit, to a secondary flower 
 or fruit. Or, if the fruit bo detached from the plant, these areoles may give 
 rise to adventitious roots and to vegetative shoots, thus initiating new plants. 
 
12 THE FRUIT OF OPUNTIA FULGIDA. 
 
 The facts and structures of interest in connection with these areoles are: 
 their number and distribution, the origin of the growing-point, the trich- 
 omes, the nectaries, the spines, and the bristles or spicules. 
 
 NUMBER. SIZE, AND DISTRIBUTION OF THE AREOLES. 
 
 Since there is a bud in the axil of each of the leaves of the wall of the 
 ovarj, except in the cases of 4 or 5 of the upper ones tkat are appressed 
 against the sepals, the total number of areoles formed is nearly the same as 
 that of the leaves. Mature ovaries show from 15 to 35 or (in joint-fruits) 
 even 40 areoles. But these are not by any means alike in size or in. the 
 number of organs or organ rudiments present in them. The size varies 
 from 1.5 to 3 mm. in diameter in flowers just opening, while the areoles of a 
 three-year old fruit may become 4 or 5 mm. broad by 6 or 8 mm. long ( figs, 
 4, 8, 47, 49). The areoles of the upper third of the fruit are in general 
 larger and more complexly organized, while those of the lower third are 
 usually much smaller and of very simple structure. The former are the 
 ones most likely, under satisfactory conditions, to develop further. The 
 lower ones usually grow little after the maturing of the fruit. They gTa du- 
 ally become depressed more and more deeply into the surface of the fruit, 
 till they are nearly buried from sight. The lower half-dozen areoles have 
 never been seen to give rise to either flowers or vegetative branches. Tn a 
 fallen fruit, however, adventitious roots may push out the upper border of 
 such a dormant or apparently dead areole (fig. 100). 
 
 As seen from without, the mature areole appears as a grayish yellow, 
 bulging cushion, of circular or somewhat longitudinally elongated outline 
 (figs. 4, 8, 47). The surface of this cushion is made up of the ends of 
 hundreds of spirally striated trichomes, which at first surround and overtop 
 all other rudiments in the areole. In slightly advanced areoles dozens or 
 scores of straight, barbed bristles or glochidia push from beside or beneath 
 the tuft of trichomes in the apical half of the areole. ITear the middle of 
 such a cushion may be seen the flattish tops of one or several spine-tipped 
 nectaries (figs. 14, 47, 48, 49, 50). Still later, in certain of the areoles of 
 the upper third of the ovary, the tip of the bud of a secondary flower may be 
 seen. This is at first covered by a protecting lattice made up of the peg-like 
 leaves, which push out of the cushion of trichomes, just below the crescentic 
 group of spicules and just above the nectary or nectaries of the areole (figs. 
 13, 15, 47). In the lower areoles of some of the more elongated fruits one 
 or two spines may be formed which resemble those found in the areoles of the 
 vegetative joints, but are usually weaker (figs. 13, 28). 
 
 ORIGIN OF THE GROWING-POINT OF THE AREOLE AND THE ORDER OF 
 INITIATION OF ITS ORGANS. 
 
 The growing-point of the areole becomes distinguishable at a time when 
 the subtending leaf has attained less than a quarter of its mature length; 
 that is, when it is only 0.5 mm. long. It at first consists of a very small 
 
THE FRUIT OF OPUNTIA FULGIDA. 13 
 
 gToiip of more darkly staining cells, located in the very axil of the yonng 
 leaf (fig's. 12 at x, 14 at x\ 16). With the further growth of the base of 
 the leaf the supjiorting portion of the stem and the tissue derived from the 
 axillary bud itself together push outward and upw-ard (see Goebel, 1889, p. 
 79) to form the young tubercle or mammilla (hgs. 14, 15, 50). This com- 
 binati(m structure gTOws more rapidly on the outer side, with the result that 
 the grownng-point of the areole comes to lie on the inner face of the tubercle 
 (fig. 14). This shoot apex forms a slightly bulging dome of about half the 
 length of the tubercle and facing directly toward the growing apex of the 
 flower (fig. 14). Later, by the growth of the tissues and organs arising 
 from the adaxial side of the growing-point, the upper end of the tubercle 
 becomes directed more outwardly, often at an angle of 45° with the axis of 
 the flower (figs. 15, 17, 19). The growing-point of the areole from this 
 time onward faces almost directly upward (figs. 12, 17, 20, 24). 
 
 The first nidiments to appear on the growing-point of the new axillary 
 bud are the monosiphonous trichomes, which arise on the margin next the 
 leaf. Following these trichomes there appears a nectary and more trichomes, 
 on tlie same side, and later another series of trichomes on the opposite or 
 inner margin of the growing-point (figs. 12, 17). 
 
 TRICHOMES OF THE AREOLE. 
 
 The first organs to be developed in the areole, after the growing-point 
 itself, are, as noted above, the monosiphonous trichomes. These are 
 developed in large numbers, scores or hundreds, by the proliferation of 
 many adjoining superficial cells about the gro^^'ing-point. At first they 
 appear aroimd half the circumference of the gro^nng-point on the side next 
 the subtending leaf (figs. 17, 32, 50). Soon afterward others appear, in 
 smaller numbers, on the side of the growing-point next the main axis. 
 When still later a group of spicules appears on this side of the gi-owing-point, 
 and successive nectaries on the abaxial side, both sorts of structures are sur- 
 rounded, and more or less hidden, by the masses of trichomes developed 
 about them. The youngest trichomes, when 3 or 4 cells long, are bent over 
 the growing-point (figs. 10, 50). Later, w^hen they attain their mature 
 length of 8 or 10 cells, they stand up nearly perpendicularly about the 
 gromng-point, though they may (especially in the upper portion) become 
 considerably bent or kinked (figs. 50, 51). The mature trichome consists 
 of a single row of from 6 to 10 or 12 cells. It is about 10 or 12 microns in 
 diameter at the base and three or four times this at the top. The basal cells 
 of the trichome are usually cylindrical, with thin, smooth walls, while the 
 up^Der 3 or 4 cells are often barrel-shajwd and have thickened, spirally 
 marked walls (figs. 51, 52). The terminal cell is often oval, with the 
 smaller end upward. In the older trichomes one or more of the terminal 
 cells may have fallen off, leaving the hair with a square end, commonly the 
 open end of an empty dead cell. 
 
14 THE FRUIT OF OPUNTIA FULGIDA. 
 
 There can be no doubt that these trichomes serve to protect from des- 
 iccation the growing-point of the areole and the young rudiments formed by- 
 it. In other words, they serve the function served by bud-scales, or modi- 
 fied leaves, in the axillary buds of most woody plants. The number and 
 length of these trichomes enables them completely to submerge all other 
 structures in the bud except the nectaries and the full-grown spicules. The 
 latter protrude for half their length, while the flat ends of the former can be 
 seen in surface view of the areole, each with a densely packed ring of 
 trichomes about it that have been crowded aside by the swelling of the 
 nectary. These clustered trichomes make a more eftective protection also 
 because of the enlarged, thick-walled cells at the end of each of them. The 
 lattice-like thickening of these cells enables them to maintain their form and 
 full size when dried out completely by the desiccating winds of their native 
 habitat. Whether the trichomes have other functions at any other period 
 of their existence has not been detennined. None has suggested itself to 
 the writer as probable in the course of this study. 
 
 The final fate of these trichomes has been suggested by what was said of 
 the breaking-off of the terminal cells. This process is apparently repeated 
 until the trichome practically disappears ; at least, the older areoles contain 
 large numbers of decapitated hairs, many of them with only a few of the 
 basal cells left. 
 
 NECTARIES OF THE AREOLE: THEIR DISTRIBUTION AND MORPHOLOGY. 
 
 In every areole, soon after the differentiation of its growing-point and the 
 development of a few score of trichomes, there appears among the latter, on 
 the side of the growing-point toAvard the leaf, the rudiment of a nectary. 
 In many of the smaller, basal areoles of the fruit only one or two of these 
 nectaries may be formed, and these lie close to the sagittal plane of the 
 areole (figs. 24, 47). In the larger, upper areoles, however, the nimiber of 
 nectaries may continue to increase with the growth of the areole until, by the 
 end of the first gro^ving-season, there may be 8 or 10 nectaries present in. 
 each (figs. 5, 47, 48, 49). As the areole grows year after year on the per- 
 sistent fruit, the number of living and withered nectaries may continue to 
 increase till 20 or more have been formed. iRot more than 4 or 5 mature, 
 living nectaries are present at one time, but a number of younger ones may 
 be initiated between a mature one and the growing-point before this begins 
 to shrivel. In the upper areoles of a primary ovary secondary flower-buds 
 usually appear after but 2 or 3 nectaries have been developed, and these are 
 soon crowded aside to wither as the secondary bud swells (figs. 47, 49). In 
 case secondary flowers are not formed from an areole until the second or a 
 later year, there may be many old nectaries found crowded aside or partially 
 crushed by the stalk of the enlarging secondary fruit (fig. 14). These nec- 
 taries were evidently initiated before the flower, since the latter, as we have 
 seen, involves the whole gi'owing-point of the areole (figs. 10, 12, 14). 
 
THE FRUIT OF OPUNTIA FULGIDA. 15 
 
 The youngest stage of tlie nectary seen was a low, conical projection of the 
 superficial layers of the nieristem among the trichomes immediately beside 
 (abaxial to) the growing-point of the areole (figs. 12, 50). Very soon a 
 small vnscnlar strand is differentia tod, just helow the base of the nectary, 
 which later penetrates a short distance into it (figs. 50, 5G). As the nec- 
 tary grows it widens somewhat near the top and becomes more or less con- 
 stricted at the base (fig. 17). When mature, the stalk of the nectary has 
 alx)ut three-fifths the diameter of its upper half. The top usually has a 
 small depression with a small tubercle at its center (figs. 17, 20). Some- 
 times this tubercle develops to a well-marked spine (fig. 23). These facts 
 clearly indicate, as has been noted by Ganong (1894, p. 59), that the nectary 
 is homologous with the spines that are so abundant on the joints of many 
 opuntias, but are often wanting on their fruits. The steady increase in 
 number of the nectaries is therefore strictly comparable with the constant 
 increase in number of the spines of the areole of the vegetative joint 
 {cf. p. 8)._ 
 
 The epidermis of the mature nectary is small-celled and thin-walled, 
 except at the top and on the spine or tubercle itself. Here the cells are small 
 and irregularly compacted and their walls are provided ^Ai\\ a cutin layer 
 several microns in thickness, which peels off rather readily (fig. 56). The 
 cells of the interior of the nectary seem to be little differentiated, except for 
 the occasional trace of a vascular bundle near the base. They are often 
 longitudinally elongated to 10 or 12 times their diameter and are commonly 
 pointed at both ends (fig. 56). Most of these cells in the mature nectary 
 have darkly staining protoplasts and nuclei, but a considerable number of 
 them are nearly devoid of contents except for a large, stellate crystal of 
 calcium oxalate. 
 
 The mature nectary remains plump and probably active for one growing 
 season and then, as has been suggested, it gradually withers and dries up to a 
 shriveled brown rod of scarcely a tenth the diameter of the functional nec- 
 tary. It is this shriveled mummy that persists indefinitely, year after year, 
 among the trichomes of the areole (fig. 14). 
 
 SPINES OR THORNS OF THE AREOLE : THEIR DISTRIBUTION, STRUCTURE. AND FATE. 
 
 "\Mnle spines, to the number of 6 or 8 and of a length of 3 or 4 cm., are 
 present in areoles of the vegetative joint of Opuntia fuJgida, they are usually 
 wanting from the fruits {cf. Wetterwald, 1889, fig. 18). When spines do 
 occur in a fruit there is usually but a single spine in each of only a few of 
 its areoles (figs. V), 7c). The position of this spine is essentially that of the 
 first nectary of the more normal fruits ; that is, it stands in the sagittal plane 
 of the areole, just wathin the subtending leaf. 
 
 The structure of these spines may be described briefly here, leaving the 
 fuller discussion of this and their development for a later paper in which it is 
 planned to deal more in detail with the stem. The spines initiated on the 
 fruit seldom attain the size and strength of those on the stem. They also 
 
16 THE FEUIT OF OPUNTIA FULGIDA. 
 
 often drop off with the maturing of the fruit, apparently in consequence of 
 the withering of the base of the spine. The number of spines in the spine- 
 bearing areoles of the joint-like fruits evidently increases, from year to year, 
 much as in the areoles of the stem. 
 
 Each spine consists of a slender, barbed axis or core and a glistening 
 white, striated sheath. The surface cells of the core, in the upper half of its 
 length, project outward and downward at the tip to form the extremely sharp 
 retrorse barbs (figs. 53, 54). The sheath, which at first covers the whole 
 core of the spine with a tightly fitting jacket, is made up of several layers of 
 greatly elongated and very thick-walled cells (figs. 54, 55), As the spine 
 matures it shrinks in diameter and separates from the sheath. The latter at 
 the same time contracts longitudinally, so that its tip is punctured by the 
 point of the spine. Later the basal portion of the sheath splits to several 
 strips, which are soon folded back on themselves in loops (fig. 53). The 
 result of this is that the tips, even of spines developed in the greenhouse, are 
 left naked for several millimeters. 
 
 BRISTLES OR SPICULES OF THE AREOLE: THEIR NUMBER. STRUCTURE. AND FATE. 
 
 On the inner or abaxial margin of each areole there is a crescentic group 
 of barbed, yellow, weak-based bristles, which form the only armament of 
 most fruits of this species. This curved cluster of spicules reaches about 
 one-third way around the growing-point of the areole (figs. 32, 50). The 
 tips of the older bristles lie close against the surface of the ovary just above 
 the areole. Each individual bristle is practically straight, about 50 or 60 
 microns in diameter and 1 to 1.5 mm. long. The surface of the bristle is 
 made up of thick, yellow-walled cells 5 to 8 microns broad by 100 microns 
 long. The outer ends of these cells project slightly outward and sharply 
 downward to form the characteristic barbs which make these bristles such a 
 persistent and irritating reminder of an encounter with the fruits or joints 
 of this cactus (figs. 57, 58). The cells of the interior of the bristles are of 
 slightly smaller diameter, more elongated, with clear and much thinner walls 
 (figs. 58, 59). 
 
 The bristles are the last of the several types of organs to appear in the 
 areole. Even the first of them do not appear till scores of trichomes and 
 one or two nectaries have been developed (figs. 12, 50). The rudiment of 
 the bristle is not, like that of the trichome, of a single row of cells, but is 5 or 
 6 cells across when it first pushes out from the growing-point (fig. 56). 
 The number of bristles in an areole increases with age. At the time the leaf 
 is shed the crescentic cluster about the growing-point may consist of 6 or 8 
 concentric rows of 20 to 30 bristles in each row (figs, 32, 50), In the 
 sterile areole of a four-year-old fruit this number may be double or triple 
 that just mentioned. When once formed the bristles evidently persist indefi- 
 nitely unless dislodged by browsing animals or by the development of a 
 flower or shoot from the areole. The absorption of a growing-point in the 
 production of such a flower or shoot of course puts a stop to the appearance of 
 further bristles from that areole. 
 
l^stjih Carollna^t|fe?0i'a'y 
 
 THE FRUIT OF OPUNTIA FULGIDA. 17 
 
 PERIANTH. STAMENS. STYLE. AND STIGMA: THEIR DEVELOPMENT 
 AND ABSCISSION. 
 
 The order of initiation of Uie organs of the flower is an acropetal one. 
 The series begins \ntli the fonnation of the peg-like leaves, followed by that 
 of the areoles, the sepals, and petals, all from the characteristic convex 
 groA\'ing-point like that of the stem. Then with a change in the growing- 
 point to a concave, ciip-like shape, tlie series of floral parts is completed with 
 the initiation of the stamens and carpels, or perhaps we should say with that 
 of the placentas and o^alles, which are fonned deep in the bottom of the cup 
 (cf. alsoGoebel, 1886). 
 
 The perianth of Opuniia fulgida consists of about 8 sepals, light green in 
 color, and of a like number of petals, rose-pink in color. These sepals and 
 petals are initiated about the gro^\'ing-point in the same way that the leaves 
 of the ovary are, but differ from the latter in the important particular that no 
 axillary buds are developed at the bases of the perianth members and that 
 there is no tubercle formed at the base of either sepal or petal (figs. 17, 22, 
 4Y). In mature structure also the perianth divisions differ strikingly from 
 mature leaves. Even the sepals are considerably broader and flatter than 
 the leaves, with more vascular bundles, while the obovate petals are very 
 broad and have a far more complex, reticulate vascular system than the 
 leaves (figs. 47, 64). The mature perianth opens after midday (in mid- 
 afternoon according to Lloyd, 1907). It forms a saucer-shaped flower an 
 inch or more across. A few days after opening the whole perianth falls 
 off, set free by the fonnation of a well-defined abscission layer. 
 
 The 250 stamens of the flower have filaments about 2 or 3 times as long 
 as the anthers. Each stamen arises as a dome-like elevation, 6 or 7 cells in 
 diameter, on the margin of the now concave gTOwing-point (figs. 16, 18). 
 As the stamens develop they bend inward over the growing-point, the 
 youngest ones standing nearly at right angles t^ the axis of the flower (figs. 
 17, 20). Later they swell at the end, as the microsporangia appear, and 
 gradually become more erect, but not completely so until the flower is open 
 (figs. 22, 23, 61). 
 
 The internal development of the microsporangia is apparently not essen- 
 tially different from that of the typical angiosperm. The u}>per, older 
 stamens open first, as they dry out first. The pollen-gi'ains are irregularly 
 globular, with a yellowish, pitted exine of about 4 or 5 microns in thickness, 
 and of a columnar or palisade-like sti'ucture when seen in optical section. 
 
 The carpels, the last structures of the flower to be formed, are 6 or some- 
 times 7 in number. This is clearly indicated by the number of nidiments of 
 carpels initiated around the growing-point, by the number of lobes of the 
 stig-ma, and by the number of placentas in the mature ovary (figs. 17, 31, 
 32, 33, 34). No case was observed with 5 carpels, the number found by 
 Engelmann ( 1887) in the plants studied by him. The first rudiments of the 
 carpels become evident after about 6 or 7 tiers of stamens have been devel- 
 2 
 
18 THE FRUIT OF OPUNTIA FULGIDA. 
 
 oped ; that is, when there are 6 or 7 stamens, one above the other, on one side 
 of the growing-point in a single radial longitudinal section (fig. 18). The 
 carpel rudiment at its initiation is twice as thick as that of a stamen. It 
 differs, also, in that it almost immediately bends inward above the growing- 
 point to meet its fellows and thus to complete the roof of the ovarian cavity 
 (figs. IT, 18, 19). Soon after the tips of the carpels meet they begin to fuse 
 together along their radial surfaces to form the rather stout style, which 
 incloses a papilla-lined stylar canal, that is star-shaped in cross-section (figs. 
 21, 23, 35, 37). The very tips of the carpels, for a length of 3 or 4 times their 
 diameter, remain unfused and form the stigmatic lobes. These finally 
 become 1 to 1.5 mm. long and are densely clothed with swollen, sac-like 
 hairs that serve for the attachment of pollen-grains (figs. 23, 36). Begin- 
 ning at a depth of 5 or 6 layers inward from the wall of the stylar canal is a 
 corrugated tube of conducting tissue 8 to 20 or even 30 cells in thickness, 
 through which the pollen-tube is to push its way (figs. 22, 34, 35). The 
 slender cells of this conducting layer extend upward to the very base of the 
 hairs of the pollen-receiving surface of the stigma (fig. 36). At the base of 
 the style this layer is continued downward as a series of strands reaching to 
 the roof of the ovary (figs. 22, 23, 24). The mature stigma lobes are con- 
 tinued outward and downward to form the characteristic 6-rayed or 7-rayed 
 structure seen in the open flower (figs. 30, 31). The lining of this part 
 of the ovary wall, down to the uppermost ovules, is covered by slender hairs 
 protruding into the cavity of the ovary. These probably help to conduct the 
 pollen-tubes to the micropyles. 
 
 Wot only do the carpellary lobes, which are at first transverse, grow 
 upward after meeting above the depressed growing-point, but they may 
 also often grow downward somewhat into the ovarian cavity, thus making 
 the roof of the latter lowest near the center (figs. 11, 21, 61). Transverse 
 sections of the ovary at this time may show several upward prolongations of 
 the ovarian cavity, separated from each other by the downward growth of 
 the carpels at the plane of juncture of the two carpels of each pair. The 
 impression given by such a section is that of a compound ovary with 6 or 7 
 separate cavities. 
 
 The separation and fall of the perianth, and other parts that fall with it, 
 is a complicated and rather variable process, as compared with the shedding 
 of parts in most choripetalous flowers. In about 3 days after the flower has 
 opened the withering of the sepals and petals has gone so far that all those 
 of a flower are twisted together into a cone of dry, crisp remnants ; that is, 
 the parts of the flower do not drop off individually, as usually happens in 
 choripetalous angiosperms, but the whole series of sepals, petals, stamens, 
 and in some cases even the style, are cast off from the ovary at once, all 
 attached to a cup-like common base stripped off from the upper end of the 
 ovary. This wholesale shedding of the floral parts is accomplished by the 
 formation of a highly developed abscission layer across the entire upper end 
 
THE FRUIT OF OPUXTIA FULGIDA. 19 
 
 of the ovary. The foi-m of this Layer is not a simple transverse plane, but is 
 that of an inverted cone, usually perforated at the apex. This funnel-shaped 
 layer of tissue is initiated in cells 15 or 20 layers beneath the surface of the 
 cup-like upper end of the ovary that bears the stamens, petals, and sepals 
 (figs. 23, 58, 60, 61). 
 
 In a diametric longitudinal section of the ovary this abscission layer 
 usually starts in at the base of perianth, either outside the sepals or, more 
 rarely, between these and the petals. From here it extends downward, 
 parallel to the surface of the cup at the top of the ovar^^, to a level just a 
 little above the base of the style, where the abscission layer again comes out 
 to the surface of this cup (figs. 23, 24, GO, 68). Less frequently the more or 
 less developed abscission layer may extend across beneath the bottom of the 
 cup at the top of the ovary. In this latter case the style is cut off, along with 
 the stamens and perianth attached to the same complete, shriveled funnel 
 (fig. 61). In the more usual case, first noted, the perianth and stamens only 
 are borne on a shriveled funnel that is perforated at the base, while the style 
 is shed separately, breaking across just above its base (fig. 24). In rarer 
 cases, where the abscission layer starts in at the top within the perianth (fig. 
 23), the i-)etals and sepals must evidently be cut off separately. Whether a 
 real abscission layer is developed in each part or not was not determined. 
 
 The first origin of the abscission layer across the top of the ovary is evi- 
 denced by a swelling, chiefly a radial elongation, of a continuous layer of 
 cells in the midst of the wall of the ovary, in the region stretching between 
 the base of the perianth and the base of the style (figs. 61, 68). Apparently 
 any cells along the line of the abscission layer to be may take part in its 
 formation, except such specialized cells as those of the vascular bundle, the 
 mucilage cells, and the crystal-holding cells. The cells that are to form 
 the abscission layer increase in radial length to about twice their tangential 
 diameter. Then the cells divide tangentially into two nearly isodiametric 
 cells (figs. 67, 68). A further tangential division follows very soon in each 
 of these cells, resulting in the formation of a row of 4 cells, of which the two 
 middle ones have only half the radial thickness of the two outer (fig. 67). 
 It is at this stage, or sometimes after one or two further tangential divisions, 
 that abscission occurs. The details of possible changes in the radial walls of 
 tlie abscission cells have not been studied. (See Lloyd, 1914, p. 70, and 
 1916, pp. 213-230). It is clear, however, that in consequence of the shrink- 
 ing of the perianth, on drying, the delicate radial walls of the thin, tubular, 
 cambium-like cells in the middle of the abscission layer are niptured. The 
 separation occurs first at the base of the perianth and continues do-v\mward 
 until the whole top of the ovary, bearing perianth and stamens, and clasping 
 the style within, curls together and droj)s ofi^ the flower on the second or third 
 day after its opening. The surface left at the top of the ovary after the 
 shedding of the periantli shows cleaidy that the break tiikes place in one of 
 the thin cells in the middle of the abscission layer, and also that it occurs 
 in the radial wall rather than as a split between two tangential walls (fig. 
 
20 THE FRUIT OF OPUNTIA FULGIDA. 
 
 62 ) . Whether or not there is a preliminary softening of the cell-walls of the 
 abscission layer, there is evidently a change in the cell-walls of the vascular 
 bundles in the line of fission, as these become flabby and distorted before 
 abscission occurs (fig. 68). Mucilage cells lying in the line of fission are 
 usually not traversed by it, but cells within or without these become trans- 
 formed into abscission cells (figs. 61, 68). 
 
 The lining of the funnel left at the toj) of the ovary after abscission is thus 
 made up, from the outer edge of the funnel do^vn nearly to its bottom, of the 
 thin-walled cells derived from the abscission layer. Immediately after 
 abscission the outermost cells dry and shrivel (fig. 62), while cells just below 
 the surface begin the production of the protective layer of cork cells which 
 will be noted in describing the fruit (fig. 63). The very bottom of the 
 funnel left after abscission is in most cases formed by the short stump of the 
 style, which is apparently cut off by an irregmlar transverse rupture of the 
 cells without the formation of any distinct abscission layer. The wall of the 
 funnel for a millimeter just above the stump of the style is still lined by the 
 epidermis (fig. 24). Only in those cases where the abscission layer cuts 
 across below the base of the style (fig. 61) is the corky lining of the funnel 
 complete from the start. 
 
 MORPHOLOGY OF THE OVARY. 
 
 The flower of this species of Opuntia, like that of any angiosperm, is to be 
 regarded as a branch of the shoot which bears carpels, stamens, petals, etc., 
 instead of the usual photosynthetic leaves, but it is unusual, or indeed almost 
 unique, in retaining a large series of the characteristics of the vegetative 
 shoot. This is indicated clearly by certain features of its earlier develop- 
 ment, by the occurrence on it of photosynthetic leaves with axillary buds, and 
 by the occasional presence on it of spines, like those of the vegetative shoot. 
 Further evidence tending in the same direction is offered by the persistence 
 and secondary growth of the fruit, by the vegetative multiplication of the 
 flower and fruit, and, finally, by the occurrence of many types of structures 
 intermediate between the tjq^ical fruit and the typical vegetative joint. In 
 this assemblage of peculiarities the flowers of this and certdiin allied 
 opuntias are unique, so far as I can learn from published records. In the 
 allied genus Peireskia the primary flower does, it is true, bear several pairs 
 of green leaves, "udth buds in their axils, and 2 or 3 of these may give rise to 
 secondary flowers. Tertiary flowers, however, are more rare, as far as I 
 have learned, and clusters of more than 3 or 4 mature fruits have not been 
 seen. ISTo record has been found of these axillary buds of the ovary giving 
 rise (either before or after the separation of the fruits from the plant) to 
 vegetative shoots of the sort formed by fruits of Opuntia fulgida. In the 
 genus Cereus also something of the same kind evidently occurs at times. 
 Thus Harris (1905, p. 535) describes briefly the occurrence, in a specimen 
 of Cereus hoxaniensis, of " several teraiinal fruits, one of which had other 
 flowers developing from the side." A section of one of the (primary ?) 
 
THE FRUIT OF OPUXTIA FULGIDA. 21 
 
 fruits showed it to be sterile. No information is given conceniing the 
 presence of axillary buds on the primary fruit, though it is clear that these 
 must have been present to initiate the secondary flowers. 
 
 The nearest approach to this structure of the wall of the ovary in these 
 CactacesB of which I find record in any other family is seen in the genus 
 Calycanthus. In this form the greatly developed floral axis is depressed at 
 the top to form a cup, from around the edges of which arise the perianth 
 members and the stamens. The numerous distinct carpels, on the contrary, 
 are developed from the bottom of this cup and remain surrounded by it, but 
 do not play any part in roofing it over, as the carpels of the Opuntia flower 
 close above its concave growing-point. The outer wall of the cup of this 
 fruit of Calycanthus bears the scars of many fallen petaloid floral leaves, 
 distributed much as the leaf-scars and areoles are over the fniit of Opuntia 
 fidgida. A study of the development of the flower of Calycanthus shows, 
 however, that there are no axillary buds above its leaves. There is not even 
 the smallest recognizable rudiment of this, and hence no possibility of the 
 development of secondary flowers or shoots from the wall of the flower or 
 fruit. 
 
 The facts of development and structure suggested in the paragraph before 
 the last, together with those detailed earlier in this paper, furnish important 
 if not conclusive evidence regarding the morphological nature of the ovary of 
 this opuntia. To the writer these facts seem to offer very strong evidence 
 for the view that the flower of the opuntias consists of a shorter or longer 
 vegetative joint, into the depressed upper end of which the ovary is com- 
 pletely submerged, and around the margin of which the stamens and 
 perianth members are inserted. This view has been advanced in more or 
 less definite form by various workers on the Cactacea; in the past. (See 
 Schumann, 1894, p. 168; Zuccarini, 1844; Toumey, 1905, p. 235; Harris, 
 1905, etvC.) The evidence for this view, however, has hitherto always 
 seemed somewhat inadequate. Since it is felt that the present study offers 
 the most complete chain of evidence thus far produced, especially from the 
 developmental standpoint, this evidence will be stated here in some detail. 
 
 In the first place the external structure of the ovary at the time of opening 
 of the flower is very like that of a vegetative joint, having prominent mam- 
 milla?, each of them bearing a conical leaf and a bud in the axil of the latter, 
 and (rather rarely) a spine like those of the stem itself. As stated above, 
 the ovaries, and the fruits formed from them, differ markedly in length and 
 breadth. Thus, the basal part of the ovary may sometimes be short, witli 
 relatively few mammilla? and areola^, and so give rise to a nearly globular 
 fruit in which the ovarian cavity reaches nearly to tlie base (figs. 11, 24, 26, 
 27). In other cases the basal portion of the ovary may be far more 
 developed, with 20 or even 30 tubercles, and the ovarian cavity may occupy 
 only the upper third or fifth, or even less, of the portion of the whole floral 
 joint below the perianth (figs, lb, 28). lu these extremely long flowers the 
 
22 THE FEUIT OF OPUNTIA FULGIDA. 
 
 surface of tJie ovary at the base may be much more stem-like than at its upper 
 end, having more prominent tubercles and furnished with areolae that not 
 infrequently bear a spine or two each. ISTot only do the real functional 
 flowers and f iiiits differ considerably in size and in the relative development 
 of parts, but the semblance to the stem may go so far that the perianth fails 
 to open, or even fails to develop completely, or (in extreme cases) the carpels 
 or ovules or even the ovarian cavity itself may never be initiated at all. 
 
 Perhaps the small, smooth joiutlets or pseudo-fruits mentioned by 
 Toumey (1905, p. 531) are to be regarded as the final members of this series 
 of simplified fruits. These pseudo-fruits occur in more or less dense, fruit- 
 like clusters, which Toumey says are particularly abundant in adverse sea- 
 sons, when true fruits are less abundant. Such structures resemble true 
 fruits in the lack of spines and in the less marked tubercles, but differ in 
 having no trace of a flower or a perianth scar at the terminal end. 
 
 These joints (intermediate in character between flowers or fruits and 
 normal vegetative joints) occur still more frequently in the allied species 
 Opuntia leptocaulis, in which practically all degrees of reduction of the 
 floral parts can readily be found. Perhaps as complete a series could be 
 found for 0. fulgida after long search, but the intermediate types are far 
 more abundant in 0. leptocaulis (figs. 89, 96). In the platopuntias also 
 joint-fruits quite similar in character to those of 0. fulgida are not really 
 infrequent where large numbers of these plants can be examined in the field. 
 The stem-like character of these joint-fruits is still more clearly indicated in 
 these forms, because the normal joints are flat, while the fruits are usually 
 barrel-shaped or obconcial. A nimiber of examples of these unusual fruits 
 of the flat opuntias have been mentioned in the literature, chiefly on plants 
 growing in greenhouses. Most of these abnormal structures have rather 
 typical perianths, sporophylls, ovarian cavities, etc., but the wall of the 
 ovary, instead of being as usual a radially symmetrical structure, grows out 
 on two sides to wing-like expansions. This gives the whole structure the 
 appearance of a disk-like vegetative joint with a thicker ovary embedded in 
 its upper margin. This ovary may be at the very top or down more or less 
 on the lateral margin of the disk. 
 
 Secondly, the intenial structure also of the ovary of Opuntia fulgida is 
 essentially like that of the vegetative joint. Thus the organization of the 
 areole, the photosynthetic system, and the vascular-bundle system are alike 
 in the two structures, except for the additional vascular branches supplying 
 the perianth and sporophylls of the flower (fig. 28). 
 
 A third feature in which the fruit of Opuntia fulgida resembles the vege- 
 tative shoots of the same plant is in its ability to persist for some years on 
 the parent plant and to continue to grow in thickness year after year by a 
 well-defined cambium layer. This point is dealt with in more detail else- 
 where (see p. 29). 
 
 Fourthly, the capacity mentioned elsewhere for self-propagation by the 
 attached flower and that of shoot-production by the fallen fruit are still 
 
THE FRUIT OF OPUNTIA FULGIDA. 23 
 
 other features in which these structures resenihlo the v('<;ctativt'. joints of the 
 shoot. 
 
 Fifthly and lastly, the whole history of development of the flower and 
 fruit, when compared with that of the vegetative shoot, shows clearly that the 
 whole lower portion of the ovary, up to the perianth, is developed by a convex 
 growing-point, in every respect just as a branch of the stem is. It is evident 
 that if the growing-point of a flower, when once initiated, continues its activ- 
 ity but a short time before the members of the perianth are laid down, the 
 ovary of that flower will have only a short vegetative portion, and the ovarian 
 cavity will occupy a considerable portion of the whole length of the ovary 
 (figs. 23, 25). If, on the contrary, the growing-point that is to form a 
 flower continues longer to form leaves, areoles, tubercles, etc., there may be a 
 long stretch of vegetative axis developed Ijefore the perianth and sporophylls 
 are initiated. Thus the ovary proper may occupy but a small portion of the 
 upper end of the whole segment or joint which is the product of the continu- 
 ous activity of this individual gromng-point (figs. 7b, 1c, 28). 
 
 The comparison of figures 17, 19, 22, and 23 shows clearly that the ovary 
 of this cactus is really secondarily submerged by the upward and inward 
 growth of the portions of the axis just below the perianth. The result of 
 this growth is that the ovarian cavity, at first formed on a level with the 
 uppermost areoles (figs. 16, 17), is buried more and more deeply by this 
 growing upward and rolling inward of the parts of the wall of the ovary that 
 were laid do^vn before the cavity of the ovary had appeared. This ditfer- 
 ential growth, which, during the ontogeny of the organ, buries the originally 
 nearly superficial and terminal ovarian cavity, until it lies near the middle 
 in the older flower and fruit, suggests clearly the probable phylogenetic 
 origin of the type of fruit found in this opuntia. 
 
 A very striking feature of shoot development in these opuntias is the 
 marked constriction usually formed at the limits marking the growths of the 
 same growing-point in successive seasons. This corresponds, of course, to the 
 boundaries marked by the winter bud-scale scars on the shoots of woody 
 dicotyledons. The anatomical reasons for this constriction in these opuntias 
 are not entirely clear. Apparently the protective structures formed about 
 the terminal bud of the annual shoot at the end of the growing-season render 
 the tissue here firm and incapable of swelling out in the follo^ving spring to 
 the thickness of the middle portion of this shoot. 
 
 The characteristic origin of the flower in the cylindropuntias is also, as 
 we have seen, from a new axillary bud which develops a flower with its longer 
 or shorter ovary in the same season that it pushes out of the areole. In cer- 
 tain rare instances in Opuntia fulgida, 0. spinosior, and in others seen in 
 0. cylindrica, growing at Del Monte, California, the part of a flower-forming 
 joint, containing the ovarian cavity, was marked off from the basal portion 
 only l)y a veiy slight narrowing of the joint. Such structures seem to indi- 
 cate that the same growing-point may sometimes develop continuously either 
 
24 THE FRUIT OF OPUNTIA FULGIDA. 
 
 during the same season, or more probably for two successive seasons, forming 
 a vegetative axis in the first and a flower and fruit in the second. This at 
 least is the most plausible explanation that suggests itself of the origin of 
 such structures as those shown in figures 7c and 88, where nothing but a very 
 slight constriction separates a well-developed fruit from a vegetative joint of 
 the usual length of a yearns shoot. 
 
 This same sort of change in the nature of the product of a growing-point, 
 either between the beginning and end of the same growing-season or in suc- 
 cessive seasons, will probably prove to be the explanation of the origin of 
 certain combination joint-fruits found in the flat-jointed opuntias. 
 
 The most interesting problem concerning the development of joint and 
 fruit in these cacti is, of course, that of the cause determining that, up to a 
 certain stage in the history of the gromng-point of each flower-rudiment, 
 there shall be formed photosynthetic leaves, tubercles, and areoles only, while 
 beyond this point the course of development is so changed that thereafter 
 nothing but floral structures are laid down about the margin of this identical 
 group of initials. The fact that this change in the character of the rudi- 
 ments produced on the growing-point occurs at different times in different 
 flowers of the same plant seems to indicate that the conditions controlling 
 this are somewhat local in nature. Such experimental attempts as were 
 made to change the fate of the structures organized about the growing-points 
 of very young flowers, by removing the persistent fruits bearing these young 
 flower-buds, gave no clue to the cause or nature of the change in character of 
 these rudiments. These experiments did, however, show that when the 
 change has once occurred the character and fate of these buds of the areoles 
 are not reversible. In other words, if a fruit of Opuntia fulgida is plucked 
 in February or March and placed in moist sand, certain of its areolesi 
 will give rise to vegetative shoots. If, on the contrary, the fruits were picked 
 and planted in April, after the floral structures have been initiated, these 
 same areoles wither without giving rise to any permanent structures {i. e., 
 shoot-buds) such as would have been formed by these very same areoles if 
 picked a few weeks earlier. Further experiments are being undertaken in 
 the hope of discovering the material or responsive basis of this change. 
 
 It would seem, then, that we have strong evidence, from its structure and 
 development, for believing that the present type of fruit in Opuntia has 
 arisen from an originally superior ovary which has progressively sunken 
 more and more into the upper end of the joint bearing it. However, as 
 Harris (1905) has pointed out, there is as yet no adequate evidence for con- 
 cluding with Toumey (1905) that this submergence has occurred very 
 recently in the phylogeny of the genus or family. It is still possible, of 
 pourse, that Opuntia is a less-modified type of a series of which Cerev^, 
 Echinocereus, and Echinocadus are more highly evolved members. In the 
 latter genera the wall of the ovary may bear numerous bract-like leaves 
 resembling those of the opuntias and often also bear axillary areoles, having 
 more or less abundant trichomes and in some cases one or several spines. 
 
THE FRUIT OF OPUNTIA FULGIDA. 25 
 
 THE FRUIT: ITS STRUCTURE. PERSISTENCE. AND FATE. 
 NORMAL AND ABNORMAL. 
 
 The fruit of Opuntia fidgida occurs, as we have seen, in ehisters of from a 
 dozen to a hundred or more depending from one vegetative joint or even, from 
 a single parent frnit (figs. 2, 3). The individual fruit may he globular in 
 form, or barrel-shaped, pear-shaped, or still more elongated and nearly cylin- 
 drical (figs. 3, 4, 7, 26, 28). It may have a diameter of from 20 to 35 mm. 
 and a length of from 25 to 65 mm. Its size differs with the plant and with 
 its position in the cluster. The terminal and younger fruits are usually 
 smaller, but sometimes those of any one growing-season seem small through- 
 out. The surface of the upper or terminal end of the fruit is formed by the 
 cork-covered scar left by the fall of the perianth and stamens. This scar is 
 decidedly concave when young, but with age it flattens out or, in some 
 cases, even bulges slightly at the center (figs. 3, 25, 28). The lateral sur- 
 face of the fruit when young has markedly developed tubercles, or mammil- 
 lae, each terminating in a leaf-scar and its accompanying areole (figs. 4, 17, 
 31, 32, 47). These tubercles become less prominent as the fruit grows 
 older and at last nearly disappear, though traces of them are seen in the 
 pentagonal or hexagonal form, in cross-section, of older fruits (figs. 3, 
 26, 43). 
 
 The internal structure of the fruit is far more variable than that of the 
 exterior. It may have no seeds at all or it may contain anywhere from 1 ta 
 200 or more seeds. These seeds may all be shriveled, partially developed 
 rudiments, or from a few to most of them may possess normally matured 
 embryos. The number, condition, and structure of the seeds seem to show 
 no correlation with the external form of the fruit (figs. 25, 26, 28). 
 
 The most striking peculiarities of the fruit of this Opuntia are, as 
 suggested above, its failure to ripen, its persistence on the plant, its long- 
 continued gi'owth, and finally its capacity for proliferation, whether left 
 attached to the parent plant or torn loose from it. 
 
 THE FRUIT AT THE TIME OF ABSCISSION OF THE PERIANTH. 
 
 With the dropping from the ovary of the stamens and perianth we have 
 left the earliest stage of the fruit proper. Externally, the fruit so formed is 
 a globular or obconical structure, with a very deep, funnel-like depression in 
 the top and from 15 to 40 strongly raised tubercles on its sides. Each of the 
 latter bears a leaf-scar and a more or less developed areole at its upper end, 
 which was mentioned in describing the ovary of the flowers. 
 
 In internal structure this young fruit consists of the superficial epidermis, 
 which is soon continued over the leaf-scars and perianth-scars by a corky 
 periderm. Below the epidermis is the 4 or 5 layered hypodennis, consisting 
 of an outer layer of crystal-holding cells, and within this of 3 or 4 layers of 
 collencliymatously thickened cells, in which the cell-cavity is finally to be 
 nearly obliterated (figs. 71, 72). Within the hypodermis are the elabor- 
 
26 THE FEUIT OF OPUNTIA FULGIDA. 
 
 ately ventilated, photosyntlietic palisade of the cortex, with its scattered 
 slime-cells and crystal cells, and the complexly reticulated vascular system ; 
 and, finally, within the latter and between its meshes are many layers of 
 mucilaginous storage parenchyma. The latter in turn surrounds the cavity 
 of the ovary, now nearly filled by the young seeds and by the mass of loose 
 tissue arising from their long, coiled, funicular strands (fig's. 23_, 40, 71). 
 
 The somewhat uneven outer layer of the epidermis of the projecting 
 tubercles consists at this stage of rather cuboidal cells, with bulging and 
 considerably thickened outer walls (fig. 71). The epidermal cells of the 
 gTooves between the tubercles are somewhat elongated radially and thinner- 
 walled than those of the outer margins of the tubercles just described. 
 Stomata are scattered rather frequently over the surface of the tubercles. 
 The guard-cells are already sunken considerably below the surface, though 
 not as far as in the mature fruit (figs. 71, 72). The inner layer of the epi- 
 dermis already includes many crystal-containing cells of the sort figured in 
 detail in the older fruit (fig. 71, 72, 73). 
 
 The cork of the fruit at this stage is confined to the pit-like scar at the 
 top of the fruit, where it forms an ashy-white layer. It consists, outside the 
 phellogen, of above 8 to 10 layers of rectang-ular cells approximately 100 
 microns long and broad and 20 to 40 microns thick, radially. The walls of 
 all save one layer of these are not greatly thickened, nor apparently strongly 
 suberized (fig. 63). The very bottom of this cup around the stump of the 
 style is commonly still protected only by the original epidermis, which, as 
 was noted earlier, is often not cast off along with that part of the lining of the 
 cup which bears the stamens (figs. 23, 60). 
 
 The photosynthetic tissue of the ovary-wall has already beg-un to assume 
 the striking arrangement in radial rows that is so characteristic of the 
 cortical tissue of the mature fruit as well as of the vegetative joint (figs. 39, 
 70, 71, 73). Scattered abundantly through this palisade, which extends 
 inward 8 or 10 cells from the surface, are numerous mucilage-cells of the 
 usual more rounded form. 
 
 The vascular-bundle system of the young fruit consists of about 16 pri- 
 mary bundles entering it at the base. These soon divide by dichotomous 
 forking to form twice as many biuidles at the level of the lower end of the 
 ovarian cavity. The repetition of this forking gives rise in the upper half 
 of the fruit to a still more complex system of main vascular bundles (figs. 
 17, 21, 25,26). From the points of forking of these main bundles are given 
 off the groups of smaller bundles, one group at the base of each tubercle, to 
 supply the tubercle, its growing-point, and the leaf and nectaries arising 
 from it (figs. 21, 27, 28, 32). The main vascular bundles are nearly isodia- 
 metric in cross-section at this stage of development, and are about 500 
 microns thick radially and 300 microns broad tangentially (fig. 44a). In 
 internal structure, which may be noted briefly for comparison with the 
 bundle of the older fruit, each main bundle includes about 25 or 30 tangen- 
 
THE FRUIT OF OPUNTIA FULGIDA. 27 
 
 tial layers of xjlem elements. Outside of these lies a group of 6 or 8 layers 
 of radially arranged cambium-cells and their little modified derivatives. 
 Still further outward on the same radius is the half-cylindrical strand of 
 phloem-cells, about 15 to 20 cells thick radially (fig. 44a). From a ring 
 of anastomosed bundles near the rim of the funnel at the top of the fruit 
 a series of downward-growing branches gives rise to the 6 or 7 pairs of 
 placental bundles, one pair running longitudinally behind each double row 
 of ovules (figs. 11, 22, 23, 26, 28, 38, 39, 41). From this same vascular 
 ring numerous small branches grow inward and upward. These are the 
 ones that supplied the stamens and perianth members before they were shed. 
 Other similar branches grow still farther downward and then turn upward 
 to form the 6 or 7 bundles of the style and stiginas (figs. 20, 22, 23, 28, 37, 
 41,61). 
 
 The most important structures within the fruit — the seeds — arise, as we 
 have seen, in a double row on each of the 6 or 7 placentae. There are from 8 
 to 12 or more young seeds in each row, making from 100 to sometimes 200 
 or more seeds that are initiated in the finiit as a whole. Usually not all of 
 these mature. Sometimes, as noted above, none of them mature. At the 
 time the perianth is dropped there is a decided difference in size among the 
 seeds present in any one ovary. The most developed are about 0.5 mm. in 
 diameter inside the pocket of the funiculus in which each seed is inclosed 
 and about 0.25 mm. thick. The seed-coats are unthickened and have only 
 
 2 layers of cells each. The embryo sac has usually reached the 8-nucleate 
 stage. The cavity of the ovary is at this time about half filled with the seeds 
 and the swollen funiculi or seed-stalks. 
 
 THE MATURE FRUIT. 
 
 At the end of the growing-season, which in Tucson terminates about the 
 middle of October, the fruit has attained what must be regarded as a mature 
 stage. The seeds within it are now full grown. These mature fruits, of from 
 
 3 to 5 months' growth, differ considerably in shape and size. They are 
 commonly pear-shaped, or somewhat more rounded, and have a diameter of 
 12 to 15 mm., with a length of 20 to 35 mm. or more (figs. 3', 7, 8). Later 
 fruits of the season may be as large as, or even larger than, the earlier ones. 
 Fruits of one season may average in all dimensions larger than those of the 
 season before. 
 
 The surface of the typical fruit at maturity has filled out so that the 
 tubercles have lost their prominence. The areoles differ in size on the same 
 fruit, the upper or larger ones at this time being 15 to 30 or even 35 mm. in 
 diameter. Occasionally an elongated fruit will be formed which has much 
 the appearance of a mammillate vegetative joint, except for the presence of 
 the perianth-scar at the top and the fact that the spines are weaker than in 
 most joints (fig. 7). 
 
 The most important features of the internal structure of the fruit are those 
 concerned with the vascular bundles of the wall of the ovary and with the 
 
28 THE FRUIT OF OPUNTIA FULGIDA. 
 
 character and contents of the ovarian cavity. The main vascular bundles of 
 the wall increase only moderately after the fall of the perianth, though they 
 do increase somewhat in radial dimensions by the addition of new layers of 
 xylem tissues (fig. 44&). The amount of the cortical parenchyma outside 
 the vascular bundles may also increase somewhat, and this latter growth is 
 probably the cause of the rounding out of the fruit and the disappearance of 
 the mammillse (figs. 3, 76, 8). 
 
 The number and character of the seeds present in different fruits differ 
 markedly. There may sometimes be an ovarian cavity filling three-fifths of 
 the diameter of the fruit, or this cavity may be practically wanting. About 
 half the mature fruits contain one or more ripe seeds, which vary in number 
 from 1 to 100 or 200 per fruit. The other half of the fruits have only small 
 ovarian cavities in which the seed rudiments have ceased their development 
 at different stages from half-formed ovules up to half -grown seeds (fig. 23). 
 In some cases not even these withered rudiments can be found in the place 
 where the ovarian cavity should be. 
 
 A consideration of the facts related inclines at first to the conclusion that 
 ovaries mature into fruits only when pollination has occurred and that seeds 
 form only when the further process of fertilization has taken place. This 
 seems doubtful, however, in view of the fact that many seeds may go half- 
 way through their development before degeneration sets in. The attempt is 
 being made to determine the distribution of these different types of degenera- 
 tion in different plants and different flowers of the same plant. 
 
 The most striking peculiarity of these mature fruits is that they do not 
 ripen. From analogy with all other fruits, we should expect at this time 
 that the flesh of the Opuntia fruit would either change color and soften or 
 harden up to form a dry fruit. But nothing of this sort happens. The 
 matured fruit, with its color still bright green, with its photosynthetic tissues 
 still active in starch-making, and its well-established fascicular cambium 
 simply halted until the next spring, enters into the resting-period of 4 or 5 
 months. There is not the slightest sign of ripening or any change at all 
 comparable with this process. There is no preparation of any sort for the 
 discharge or escape of the seeds to conditions conducive to germination. 
 On the contrary, the majority of the mature fruits normally remain attached 
 to the parent shoot, not merely through the succeeding fall and winter, but 
 season after season for several or many years. These persistent fruits 
 become essentially a part of the vegetative shoot, performing not only the 
 photosynthetic function of a vegetative joint, but also budding out new 
 shoots. Usually these shoots arising from attached fruits are floral shoots. 
 More rarely a vegetative joint may arise from such a fruit, and then the 
 latter becomes a constitutent joint of the vegetative branch, undistingiTish- 
 able except by its perianth-scar and usually by its lack of spines (fig. 79). 
 The fate of a fruit in these respects is the same, whether it contains many 
 fertile seeds or whether, as may often be the case, it is entirely seedless. 
 
THE FRUIT OF OPUNTTA FULGIDA. 29 
 
 THE PERENNATING FRUIT: ITS STRUCTURE AND SECONDARY GROWTH. 
 
 The matured fruits of Opuntia fulgida not only do not ripen at the end of 
 the growing-season, but (as noted above) they are neither shed from the 
 plants as most fruits are, nor do they open in any way to discharge their 
 seeds. On the contrary, these fruits remain year after year, attached and 
 actively growing, until they may become 40 or 50 mm. in diameter and 70 
 or 80 mm. long. The growth of these fruits in length must be chiefly 
 primary ; that is, each fruit attains practically its maximum length during 
 its first season's growth. Thus the longer fruits mentioned must have been 
 exceptionally long at the start. 
 
 Growth in thickness of the larger fruits is, on the contrary, largely 
 secondary. It is accomplished by the persistent activity of the fascicular 
 cambium and by the general multiplication of the parenchyma cells between 
 the bundles. Whether there is an increase in the central medullary 
 parenchyma of the fruit has not been determined with certainty, but 
 there appears to be some little increase in the interior diameter of the 
 vascular ring. The cortical parenchyma, inside the hypoderm, may in- 
 crease in thickness from about 2 mm. in the just-matured fruit to 5 mm. 
 or more in a fruit several years of age. This radial growth seems to be 
 almost entirely a result of the radial elongation of the cortical cells, as the 
 number of these along a radius ranges from 20 to 25 in both the just-matured 
 fruit and in that 3 or 4 years old. 
 
 The fascicular cambium of the perennating fruit gives rise to numerous 
 phloem and xylem elements, which increase the radial dimension of the 
 bundle from O.Y or 0.8 mm. in the newly matured fruit to 3 or 3.5 mm. in a 
 fruit several years old. The radial extent of the xylem in the newly formed 
 fruit is about 0.6 mm. and that of the phloem 0.2 mm., while in an older 
 fruit the dimensions are 2.6 mm. for the xylem and 0.6 mm. for the phloem. 
 This shows that the growth of the two tissues has kept their bulk much the 
 same relatively. The tangential growth of the bundles is relatively slight, 
 the outer edge of a bundle 4 or 5 years old being only half as wide again as 
 that of one in the first-year fruit. ISTo definite annual rings could be dis- 
 tinguished in the wood of these older fruits. The number of larger xylem 
 elements along a single radius in a young fruit is about 25, while in a 4 or 5 
 year fruit there may be 80 or 90 vessels on a single radius. 
 
 The parenchyma of the pith-rays differs from that of the cortex by show- 
 ing a vigorous cell multiplication. The pith-ray of the just-matured fruit 
 may have but 8 or 10 cells in the radial extent of the bundle, while in a 
 fruit 4 or 5 years old a pith-ray may be made up of 25 or 30 cells in the 
 radial width of the bundle. This growth is apparently due to the general 
 division of cells throughout the ray, as no trace of an interfascicular 
 cambium is discoverable. 
 
 Two structures only on the surface of the fruit undergo important changes 
 as the fruit ages. These are the corky periderm and the areoles. At the 
 
30 THE FRUIT OF OPUNTIA FULGIDA. 
 
 end of the season of its origin the fruit is protected by the well-cutinized 
 epidermis and the underlying hypodermis, except for the perianth-scar and 
 the individual leaf-scars. This epidermis persists over the general surface 
 of the fruit for several years. Only where the epidermis is cracked by the 
 swelling of the fiTiit or is otherwise injured is the original protective layer 
 replaced in function by cork, like that of the perianth-scar. 
 
 The periderm of the perianth-scar has its origin, as we have noted, from 
 a pliellogen layer arising in descendants of the original cells of the abscission 
 layer, just within the plane of abscission (figs, 62, 63). The first 5 or 6 
 layers of cork cells formed by the cork cambium are very thin-walled ; then 
 there is formed a single layer of very thick cells (see Wolfe, 1912, figs. 6, 
 7, 9). These sclerenchyma-like cells have walls of a pale-yellow color, 
 which in older fruits are made up of from 15 to 20 distinct layers marked by 
 numerous minute radial pits (figs. 63, 64, 65). The walls stain intensely 
 with safranin and gentian violet. The cork cambium, after forming this 
 thick layer, may continue to form more thin-walled cork cells until, in the 
 older fruits, 12 to 15 or more layers are present inside the intact, thick layer. 
 These later layers are more numerous on the upper margin of the perianth 
 scar. With increasing age the 5 or 6 layers of thin cork outside the scleren- 
 chyma layer, which are left more or less shriveled after abscission, are grad- 
 ually worn off from the more exposed parts of the scar. This leaves the 
 sclerenchyma as the superficial and essentially protective layer unless this is 
 injured. When this primary sclerenchyma layer is broken a secondary one 
 is formed immediately outside the then active phellogen (fig. 14, at right). 
 
 Periderm formation in the region of the areole begins soon after the fall 
 of the leaf, in an area that includes tissue of the leaf -scar itself and a few 
 of the epidermal cells below and beside this (fig. 14). There is thus formed 
 a periderm of from 3 or 4 to 8 or 10 cells in thickness, of which the portion 
 immediately above the foliar bundle may finally include 3 or even 4 immedi- 
 ately superposed sclerenchyma layers (figs. 63, 64). As development of the 
 areole proceeds the cork layer develops upward from the leaf-scar and 
 thin-walled cork-like but apparently little-suberized cells are formed imme- 
 diately beneath the persistent trichomes, just above the leaf. Later the 
 formation of these cells continues on beneath the bases of the withered nec- 
 taries and spines if there are any, and finally beneath the bristles (figs. 14, 
 17). The latter, in older fruits, may be supported upon 12 to 15 or more 
 layers of clear thin-walled cork-like cells (fig. 14). The only parts of the 
 areoles that are not covered are the growing-point and the immediately sur- 
 rounding series of rudiments of nectaries, bristles, etc. These all lie well- 
 protected at the base of the dense tuft of younger tricbomes that overhang 
 the growing-point (fig. 50). 
 
 On the lateral surface of the older fruit corky tissue may arise by the 
 extension of the cork about the areole, or that of the perianth-scar over the 
 edge of the cup,' or it may arise de novo from injured spots in the clear epi- 
 
THE FRUIT OF OPUNTIA FULGIDA. 31 
 
 dermis between the areoles. In this way considerable portions of the sur- 
 face of a fruit 4 or 5 years old may become covered with cork developed 
 below cracks or bruised spots, and the fruit thus come to have the mottled 
 green and gray color characteristic of maturing vegetative joints (fig. 3). 
 The effect of this cork, aside from affording protection to the water-stored 
 cortical tissues, must be also to cut off the light and air from the photosyn- 
 thetic cells of the portion of the fruit covered by it. While lessening its 
 starch-making capacity, the cork is thus of prime importance to the fruit in 
 maintaining it as a supporting and conducting structure for the flowers and 
 persistent fruits that may arise from it year after year. 
 
 The structure of the areole in the young fruit has already been discussed 
 (p. 12). The chief change in the areole with increased age of the fruit 
 is the increase in size, until it may become 3 or 4 mm. broad and 6 or 8 mm. 
 long in the case of those near the top of the fruit. This increase in size is 
 due chiefly to the continued production of hundreds of trichomes year after 
 year. These appear in rather definite concentric circles around the growing- 
 point. Besides the trichomes, the areole also forms additional nectaries, 
 year after year, till at least a score may successively develop and wither. 
 The bristles of the fertile areole, as has been noted, are not increased in num- 
 ber after a flower is initiated (figs. 14, 17, 50). The sort of development 
 here indicated is the characteristic one for many of the areoles of the upper 
 half of the ovary throughout the life of the fruit. Others of the basal half 
 or quarter of the fruit may persist, but show only slight growth for 2 or 3 
 years and then cease growing altogether. 
 
 Other of the upper areoles, several in each fruit, give rise to one or the 
 other of the two most important structures developed from fruits. These 
 are the floral shoots that may arise on the attached fruit and the vegetative 
 shoot that develops from the areole of a detached fruit. These structures 
 are, of course, the normal products of axillary buds. Hence the earlier 
 period, during which these areoles are developing only modified structures 
 like bristles and nectaries, must be regarded as a sort of resting-period in 
 which the normal activity of the bud is inhibited. 
 
 When the normal development of an areole is accomplished and a shoot 
 produced, all further activity by this areole is terminated, as must be evident 
 from the fact that the whole mass of the single growing-point of the areole is 
 embodied in either the vegetative shoot or the flower. The exact conditions 
 conducive to the production of a flower in one case and a vegetative shoot in 
 another, with the details of development of each, will be described, as far 
 as kno^\Tl, in the discussion of proliferation (see pp. 35-50). 
 
 The possible activities of the fruit of Opuntia fulgida may be summarized 
 as follows: The fruit usually remains attached and in succeeding seasons 
 buds out new flowers. If fruits fall to the ground from increasing weight 
 of the cluster or when dislodged by wind or brow^sing animals, then any one 
 of three things may happen. Most frequently the fruit dries up or decays 
 
32 THE FRUIT OF OPUNTIA FULGIDA. 
 
 and nothing comes of it. If it drops on moderately moist soil, then it may 
 give rise to roots and shoots bv proliferation from the areoles. More rarely 
 still, the fruit may set the seeds free by decay and the latter may possibly 
 then germinate to seedling plants. This latter fate, which must be regarded 
 as the most normal one for such a fruit, is evidently a very rare one for the 
 fruit of Opuntia fulgida, at least in the deserts near Tucson, v^^here seedlings 
 have never been seen. 
 
 THE SEED: ITS STRUCTURE, PERSISTENCE. AND 
 GERMINATION. 
 
 The ripe seed is the one essential structure of the fruit which remains 
 entirely unchanged year after year, as the fruit persists on the parent plant. 
 
 The mature or ripe seed is an irregular, round-angled, flattened disk about 
 5 mm. in diameter and il.5 to 2 mm. thick in the middle (fig. 77). It usually 
 bulges on both sides of the disk, but often far more on one side than the 
 other. The majority of good seeds are pale yellow in color, with remnants 
 of many colorless cells from the fleshy ovule-stalks sticking to them. In 
 internal structure the seed consists of a well-developed curved embryo bent 
 in the plane of the disk-like seed, of a small remnant of endosperm near the 
 center of the seed and embraced by the bent embryo, and finally of a protect- 
 ing j acket, formed chiefly by the layers of tissue arising from the pocket of 
 the funiculus, but including also the two thin integuments (figs. 76, 77). 
 
 The embryo is from 0.7 to 1 mm. in diameter and about 4 or 5 mm. long. 
 It is bent in the plane perpendicular to that of the adjacent faces of the coty- 
 ledons. Most of the cells of both cotyledons and radicle of the embryo are 
 densely stored with what appear to be aleurone grains and slime globules. 
 These bodies take on a brownish and not a bluish color with iodine, and 
 show structural features not characteristic of starch-grains. Occasional 
 cells of the cotyledons and upper part of the radicle are completely occupied 
 each with a large cr^^stal of calcium oxylate like those found in the paren- 
 chyma of the mature plant. 
 
 The endosperm, which consists of a small mass in the bend between radicle 
 and cotyledons and of thinner layers extending along beside the radicle and 
 over the tips of the cotyledons (fig. 98), is densely stored with starch which 
 reacts in the usual way with iodine. 
 
 Small fragments of perisperai, left in the corners where the embryo fits 
 the integument less accurately, are filled with granules reacting like those in 
 the embryo itself. The cell-contents of both embryo and endosperm seem to 
 remain entirely unchanged in fruits that have persisted on the plant for 
 many years after the maturing of the seeds. The integuments are made up 
 of considerably thickened cells, the outermost layer of them with w^avy 
 brown walls. 
 
 The jacket derived from the funiculus surrounds the seed completely, 
 having finally closed in above the micropyle (fig. 97). It makes up more 
 
THE FRUIT OF OPUNTIA FULGIDA. 33 
 
 than nine-tentlis of the thickness of the coat surrounding the seed and con- 
 sists of three distinct layers. The inner layer is from 150 to 300 microns 
 thick. It consists of intertwisted threads or fibers which run meridionally 
 about the seed. The component cells of these threads are 8 to 10 microns in 
 diameter each by 150 or 200 microns long. The middle layer of the funi- 
 cular pocket is made up of somewhat similar interwoven threads running 
 equatorially, i. e., around the luargin of the disk-like seed. The cells of this 
 layer are 20 to 25 microns in diameter, but only 50 to 60 microns long. The 
 third or outermost layer of the seed-coat is very uneven, consisting of a single 
 layer of cuboidal cells 30 or 40 microns thick, about most of the margin of 
 the seed, but of Y or 8 layers with a total thickness of 400 microns on the 
 sides of the seed. It is this greater thiclmess of the outer funicular layer 
 that makes up most of the bulge on the flat side of the disk-like seed. 
 
 The whole structure and condition of the seed apparently remain quite 
 unchanged year after year so long as the fruit containing it remains attached 
 to the tree. Not only are the embryos of seeds from the oldest attached 
 fruits still plump, with the stored starch intact, but a seed from such an old 
 f niit is just as capable of germinating as one from a fruit just matured. 
 
 A very important question arising in this connection is : Why do not 
 these seeds, immersed in the moist pulp of the parent fruit and raised each 
 summer to a relatively high temperature, germinate there, without waiting 
 to escape from the fruit ? The attempt was made to germinate seeds under 
 these conditions by treating them in the manner which was found necessary 
 to secure germination outside the fruit, that is, by chipping the seed-coat. 
 Seeds with the coats cut off at one edge Avere carefully inserted in the pulp 
 of sound fruits witli every precaution not to injure the fruit more than neces- 
 sary. The wound was then sealed with vaseline and set in a moderately 
 moist chamber to induce germination. No germinations of seeds under 
 these conditions were secured. In each case, whether the injured fruit 
 dried out, decayed, or took root in the soil, the embrj^o of the inserted seed 
 after some weeks blackened and died. The explanation of this failure of 
 the seed to germinate in its oavh fruit or in the host fruit was not discovered. 
 It is, of course, possible that it may be found in the mere exclusion of oxygen 
 by the seed-coat or by the mucilaginous pulp of its OA\m or the host fruit. 
 On the other hand, it is quite possible that the osmotic or chemical character 
 of the cell-sap of the pulp surrounding the seeds is the real obstacle to 
 germination. 
 
 During two sojourns at Tucson the attempt was made to test the common 
 report that seedlings of Opuntia fulgida do not occur in the field about 
 Tucson (Tourney, 1905, p. 360). Diligent search was made for them in 
 many groves of these trees in the months of April and May of 1912 and 
 1915, but not a single imdoubted seedling of this species was discovered. 
 Examination of large numbers of fallen fniits showed no sign of germina- 
 tion of the seeds. It then occurred to the writer that a search on a cattle 
 3 
 
34 THE FRUIT OF OPUNTIA FULGIDA. 
 
 range outside the protected, ungrazed property of the Desert Laboratory 
 might show that seedlings arose from seeds that had passed through the ali- 
 mentary canals of cattle that had eaten the fruits. This search also proved 
 futile. It is of course possible that seedlings may occur in other parts of 
 the area of distribution of this opuntia, or in the Tucson region itself, at 
 other seasons. 
 
 With the hope of discovering something regarding the cause or causes of 
 this failure of the seeds to germinate naturally, the attempt was made to 
 germinate them artificially. In the first place, dozens of plump seeds likely 
 to possess good embryos were repeatedly, in spring, autumn, and winter, 
 sown on soil or on filter-paper, and put either in a warm gi'eenhouse or on a 
 warm bath at 30° to 35°. 'Not a single germination was obtained from 
 these experiments. 
 
 Other series of somngs were made of plump and apparently fertile seeds 
 from which the seed-coat had been cut or filed away at one part of the 
 margin. Out of several dozens of these cut seeds so^m between layers of 
 damp filter-paper in a gallon battery-jar, only about 8 or 10 germinated. 
 The best proportion of germinations obtained was 5 embryos out of 25 prob- 
 ably fertile seeds. 
 
 The difficulties in determining what proportion of seeds are capable of 
 germination are two. In the first place, it is impossible to tell from its 
 external appearance whether a seed has a normal, well-developed embryo or 
 not. Quite aside from the half -developed and withered seeds, there are 
 many of mature size, and apparently plump and healthy, which upon being 
 cut open reveal no embryo at all, or a discolored and shriveled one with no 
 stored material in it. Secondly, of the seeds that are cut into far enough 
 to determine whether they contain good embryos, or far enough to make 
 certain the escape of the swelling embryo from within, some may be so 
 injured as to prevent germination of any sort. 
 
 The trials made thus far show that a certain relatively small percentage of 
 the seeds of this opuntia are fertile and capable (if aided in getting out of the 
 coat) of producing normal seedlings (fig. Y6). 
 
THE FRUIT OF OPUNTIA FULGIDA. 35 
 
 PROLIFERATION OF FLOWERS AND FRUITS. 
 
 The most unique peculiarity of the flower or fruit of Opuntia fulgida is 
 its ability to produce new shoots. These shoots may be floral shoots only, 
 as in the case of the attached flower or fruit, or they may be vegetative shoots, 
 as in the case of detached fruit. This capacity for proliferation is depend- 
 ent, as has been noted, on the presence and persistence of the axillary buds or 
 areoles of the wall of the ovary. These axillary buds are unknown, as far as 
 the writer has been able to leam, on the ovary of any other family of plants, 
 and even in the Cactacese occur only in the genera Opuntia, Nopalea, and 
 Peireskia. 
 
 The structure of these areoles, with a description of the rudiments present 
 in them, has already been noted (p. 11). We have seen also that most 
 of the areoles of a flow^er and fruit may persist year after year without 
 developing anything but minor organs,- such as nectaries, trichomes, and 
 spicules. We have now to consider the very important function perfoiined 
 by certain of the areoles in their proliferation to shoots of limited or 
 unlimited growth. There are three types of proliferation by the areoles of 
 the ovary of this opuntia. In the first place, from 1 to 5 or more of the 
 areoles of the unopened flower may give rise to the buds of secondary flowers, 
 which open soon after the primary ones. Secondly, one or several areoles of 
 an attached fruit may in the first or in some later season after its develop- 
 ment give rise to primary flowers of that season. Thirdly, the areoles of a 
 detached fruit that has been separated from the parent plant after maturing 
 and placed on moist soil may give rise, first to adventitious roots and then 
 later to the characteristic joints of vegetative shoots. The fruit thus per- 
 forms the unique function of initiating a new plant by purely vegetative 
 propagation. 
 
 PROLIFERATION FROM ATTACHED FLOWER BUDS. 
 
 The primary flowers of the season arise in either April or May on either 
 the vegetative joints or the fruits of the preceding season or sometimes on 
 those of a still earlier season. These flowers are developed from the growing- 
 points of the upper areoles of the joint or fniit (fig. 47) in the manner noted 
 above (p. 9). 
 
 Before the primary flower is half-grown the buds of secondary flowers of 
 various sizes can be detected developing in from 1 to 4 or 5 of its upper 
 areoles (figs, ^a, 9&, 13). By the time the primai-y flower is ready to open, 
 soon after the middle of May at Tucson, the larger buds of the secondary 
 flowers are about one-sixth grown, and are recognizable as buds of flowers 
 rather than of vegetative shoots (figs. 9a, 9&, 47). About 4 weeks after the 
 primary flower withers and sheds its perianth, the largest secondary flower in 
 its turn opens. This occurs usually between the middle and end of June, 
 and the buds of the tertiary flow^ers are then already well developed in their 
 
36 THE FRUIT OF OPUXTIA FULGIDA. 
 
 upper areoles. In the latter part of July flowers for the fourth generation 
 of the season are developing from the areoles of the tertiary ones (fig. 6). 
 These quaternary flowers probably open during August, and since the 
 blooming-season may extend into September (Lloyd, Plant World, 1917), it 
 is probable that a fifth generation of flowers may be formed in a single 
 season. 'No undoubted examples of this, however, have thus far been seen, 
 and I have not been able personally to seek them at Tucson at the proper 
 season. 
 
 Since the fruits resulting from the four generations of flowers remain 
 attached to each other in the order of their development, it is clear that a 
 chain of fruits of at least four successive linlvs may be developed in a single 
 season. This has been recorded by Toumey (1898), who apparently 
 believed that all chains of fruits arose in this way in a single season. He 
 definitely mentions that the " proliferous fruit hangs in pendulous clusters, 
 sometimes as many as 7 fruits in a single cluster, one growing from the other 
 in continuous succession." Pie regards the persistence of fruits over winter 
 and the formation of flowers from them in the succeeding spring as a rare 
 occurrence. 
 
 The time of maturing of the seeds of the fruits of the four successive gen- 
 erations may differ considerably, since the fruits continue to grow after 
 dropping the perianth, but even the latest and smallest ones may contain 
 ripe seeds in October. All four links of the chain may commonly persist 
 attached throughout the winter and give rise to new flowers the following 
 spring. ISTot infrequently, however, the younger, quaternary fruits may 
 wither more or less during the winter and (failing to develop flowers upon 
 them in the succeeding spring) may be crowded off by the new flowers 
 developed beside them on the tertiary fruit by which they themselves are 
 borne. 
 
 The formation of these chains of fruits of four links in a single season 
 is thus the result of the continuous uninterrupted development of the grow- 
 ing-points of certain areoles of each successive floral shoot. The structure 
 thus formed is comparable with that developed by many herbaceous plants 
 and the water-shoots of certain woody ones, in which each (or many) of the 
 axillary buds develops continuously during the season of its initiation into a 
 mature vegetative or reproductive shoot. 
 
 Other areoles of the flower and fruit of this opuntia have quite an opposite 
 fate. In these the axial bud does not develop continuously, but ( after devel- 
 oping a considerable number of trichomes and spicules and a few nectaries) 
 rests till the next growing-season, or sometimes for three or four seasons, 
 before renewing its development. 
 
THE FRUIT OF OPUNTIA FULGIDA. 37 
 
 PROLIFERATION OF PERSISTENT ATTACHED FRUITS. 
 
 While certain of the upper areoles of a flower may, as we have seen, 
 develop at once into secondary flowers which open soon after the primary 
 one, other areoles of the same or another flower may practically cease growth 
 with the opening of the flower and persist over one or more winters as resting 
 buds. These buds, retaining their capacity for further development, may 
 give rise, in the succeeding or a later spring, to the primary flowers of 
 that season (fig. 4, 7c). Such flowers may arise from any of the 4 or 5 
 younger fruits of a chain (fig. 4). 
 
 The development of these flowers, arising from resting buds of persistent 
 fruits, is identical with that of flowers arising from the areoles of flower- 
 buds, and the fruits formed in the two cases can not be distinguished. The 
 flowers arising from fruits, just as those from the areoles of unopened 
 flowers, may give rise in turn to buds of secondary flowers, and these to ter- 
 tiary and perhaps quaternary ones in the same season. The repetition of 
 this process of budding out flowers from fruits and then flower from flower 
 several times each season, when repeated season after season, results finally 
 in the formation of fruit clusters of great size. Clusters of 20 to 30 fruits 
 are common, and clusters of 100 or more fruits of all ages suspended from a 
 single parent fruit are not rare (figs. 2, 3). Some of the longer chains may 
 embody 12 or 14 generations of fruits in a single chain (fig. 77). Since, as 
 we have seen, certain of the links added in any one season may wither and 
 fall off, it is evident that a chain of 12 generations of fruits does not repre- 
 sent merely the growth of three seasons, 4 fruits per season, but may repre- 
 sent the product of five or six seasons ; in fact, the size and appearance of 
 some of the basal fruits of these clusters indicates an age of more than 6 
 years. The records of the effect of exceptionally cold winters on the plants at 
 Tucson show that it must often take many seasons to build up a chain of 12 
 or 14 links. Thus, in the winter of 1912-13 there was an exceptionally hard 
 freeze, soon after which great numbers of the younger persisting fruits fell 
 off the trees, so that chains of more than 3 or 4 links were hard to find. 
 Such a periodic shortening of the chains, even if it occurred but once in 
 three or four winters, would increase considerably the number of summers 
 necessary to produce chains of fruits of the total length of the longer chains 
 found. 
 
 The ease with which these fruits may be set free from the plant will be 
 the more readily realized when we note the very slender stalks by which the 
 heavy fruits are attached (figs. 25, 26). These stalks also, especially in the 
 younger fruits, have little lignified tissue. Jarring of the tree by A\T[nd or 
 by broAvsing cattle, which eat many of the fruits in dry seasons, may shake 
 off numbers of fruits that are often found strewn thickly beneath larger 
 plants. The stalks of the older fruits, on the contrary, become steadily 
 thicker and stronger, and the upper ones are thereby enabled to hold the 
 heavy clusters that hang from them. 
 
38 THE FRUIT OF OPUNTIA FULGIDA. 
 
 PROLIFERATION OF FALLEN FRUITS. 
 
 If the fruit of Opuntia fulgida remains attached to the tree the only struc- 
 tures produced by its areoles are trichomes, nectaries, and flowers. This is 
 practically universally true. Among many hundreds examined, only two 
 cases were seen in which a vegetative shoot had arisen from an attached 
 fi-uit. If, however, fruits are plucked from the tree and placed on moist 
 soil, there arise from their areoles not flowers but roots and later vegetative 
 shoots, and so new plants are initiated ; that is, if any given fruit remains 
 attached there may arise from the growing-point of a certain areole a rela- 
 tively short shoot which develops leaves and axillary buds, but soon ends its 
 activity with the formation of a set of stamens and carpels. If the same 
 fruit were detached the same areole, and thus the very same growing-point, 
 may give rise to a shoot of unlimited growth, while other areoles near the 
 soil form adventitious roots. This production of new plants from buds on 
 the wall of the ovary in the fruit is a surprising phenomenon ; in fact, it is as 
 unique as the formation of flowers from axillary buds of the ovary of 
 the unopened flowers. 
 
 This process of the vegetative sprouting of a fruit planted in soil to a new 
 plant often occurs in 50 to 75 per cent of fruits planted in the greenhouse. 
 In the field about Tucson, at least in the spring of the year, it occurs but 
 rarely. A careful examination of some scores of young plants of this 
 species, of 3 or 4 joints in height, in the desert near Tucson, in May 1915, 
 showed that all had arisen from fallen vegetative joints. ISTone of the fallen 
 fruits seen at this time showed any preparation for the development of new 
 plantlets. This is the more surprising because the soil had been considerably 
 moistened that season by unusually copious rains. In September, however, 
 a careful search by an assistant, B. R. Bovee, revealed a few very young- 
 plants which had evidently arisen from fallen fruits. It is possible, there- 
 fore, that under some conditions, such as those existing during years of 
 favorable summer rains, a considerable number of new plants may thus arise 
 from fruits. 
 
 The origin of new plants from rooted fruits will be described as it has been 
 observed in the greenhouse. The process is clearly the same in the field, as 
 far as could be seen from the few plantlets found there. Many different 
 plantings of the fruits were made at Tucson in April and May, at South 
 Harpswell in July and August, and at Baltimore in February, October, and 
 December, These all gave substantially the same results, in spite of the fact 
 that the Tucson plantings were of fruits that would in a week or two have 
 produced flowers if they had been left on the parent plant, while those 
 planted in Baltimore had entered into the resting-stage for the winter (figs. 
 78,99). 
 
 Fruits that are half -buried in a soil that is kept moist but not saturated 
 may begin to form adventitious roots within the first week. In 5 weeks' time 
 the fruit has been found fastened securely in the soil by several roots, some 
 
THE FRUIT OF OPUNTIA FULGIDA. 39 
 
 of them 5 cm. long, 1 mm. thick, and often branched several times. These 
 roots arise chiefly on the buried portion of the fniits and always develop 
 from an areole, from the broken surface of the fruit-stalk, or more rarely 
 from near the edge of the perianth-scar. From this statement it will be 
 seen that roots may arise at either the basal or apical end of the fruit, or 
 at both, depending on whether the fruit is laid horizontally or whether one 
 end is placed lower in the soil. My observations do not confirm the con- 
 clusion of Toumey (1905) that the " roots appear chiefly at the basal end of 
 the fallen joint." Though the roots arise from the areole, they do not arise 
 from its growing-point, in the middle of the areole, but from the still active 
 tissue around its edge. Very often a root pushes out above the cluster of 
 bristles on the adaxial margin of the areole, but a root may rise also from 
 any other part of the margin (fig. 100). One or several roots may arise 
 from the same areole. When a root is developed from the scar of the fruit- 
 stalk it is usually from its margin. As such a root matures, however, the 
 vascular bundles of the root soon come to form continuations of the bundles 
 at the base of the fruit. When a root develops on a perianth-scar it appears 
 always to originate in the region of the cork cambium, and it breaks through 
 the cork itself in emerging (figs. 78, 99, 100). 
 
 The initiation of a shoot by a detached fruit does not occur until some 
 time after the first roots are developed on it. The formation and function- 
 ing of roots are apparently necessary antecedents to shoot formation. In 
 fruits planted in the greenhouse at Tucson on April 26, kept well watered 
 and at rather high temperatures, shoots began to push out of some areoles by 
 May 25, and on the following September 10 all but one or two of the 18 
 fmits planted had one or more vegetative joints on it. Some of the latter 
 were 2 cm. long. Similar results, though not so universally successful, were 
 obtained from plantings at South Harpswell and Baltimore. One lot of 
 fruits planted at Baltimore produced shoots only 3 or 4 cm. long in a year ; 
 while others, with more soil, had shoots 10 cm. long in five months. 
 
 One or several joints may arise from each fruit, either simultaneously or 
 successively. They may arise from areoles on the exposed surface of the 
 planted fruit or sometimes from those joints at the surface of the soil, but 
 nearly always from the larger areoles of the apical half of the fruit. This is 
 without regard to whether the fruit is planted on the side, -with apex down, 
 or with the base do\\ai. 
 
 The shoot arising from the areole of a fallen fruit is formed by the grow- 
 ing-point of the areole, just as a flower is, or just as a branch is from a vege- 
 tative joint. The new shoot, however, is for a long time dift'erent from the 
 branch of a mature plant in remaining slender and in the permanent delicacy 
 of its spines (fig. 78). In fact, it has the appearance of one of the early 
 joints of a seedling. The primary shoot, as developed in the greenhouse in 
 Baltimore, usually does not branch until the second season. Quite early in 
 its development the new shoots, especially if it has arisen near or under the 
 
40 THE FRUIT OF OPUNTIA FULGIDA. 
 
 soil, sends down adventitious roots of its own which soon become an impor- 
 tant part of the root-sjstem of the new plant. 
 
 From what has been said of the slow development of plantlets from 
 sprouting fruits in the laboratory, it is evident that it takes a number of 
 years to develop a mature flowering plant from a fruit. It is doubtful 
 whether such a plant can mature more than a year or two sooner than a seed- 
 ling started at the same time. 
 
 Examination of plantlets, from sprouted fruits and also of those from 
 fallen joints, shows that not all of the fallen fruit or joint enters into the 
 make-up of the first or basal joint of the new plant. The portion which does 
 so probably depends in part upon the position in which the fruit falls, or is 
 planted, on the soil and on the relative positions on the fruit of the areoles 
 forming the roots and those forming the shoots. It is a common occurrence 
 for a part (often a fourth or a third) of the fruit, including both cortex and 
 vascular bundles, to be cut off by a layer of cork from the part going into 
 the first joint of the new plant (fig. 99). The phellogen from which this 
 cork arises is formed by the parenchyma of the cortical and medullary- 
 tissues. 
 
 The fate of the different parts of the vascular system of the parent fruit 
 has not been followed out in all details, but it is clear that much of the old 
 system plays no important part in the new plant and that some of it is cast 
 off with the cut-off portion of the fruit (fig. 99). The chief part of the old 
 system to do service in the new.plantlet is that which lies most directly 
 between the point of origin of the adventitious roots and that of the primary 
 shoot of the plantlet (fig. 99). These strands quickly become thickened to 
 many times the diameter of the other bundles of the parent fruit. The seeds 
 present in these sprouting fruits evidently persist indefinitely in the flesh of 
 the latter. Their ultimate fate has not yet been determined, as the oldest 
 plantlets seen which were known to be of this origin were but 2 years old. 
 
 While roots may arise from parts of the fallen fruit outside the areole, 
 such as the scar of the fruit-stalk or of the perianth, it is apparently not pos- 
 sible for shoots to arise elsewhere than from the areole. The experiment 
 was tried repeatedly of planting fruits, all the areoles of which had been 
 destroyed by cauterization, to determine whether other superficial tissues 
 might be stimulated to produce new-shoot growing-points. Though some of 
 these cauterized fruits took root in the soil and remained plump and green 
 for 24 months, they developed no visible rudiment of a shoot. 
 
 An attempt was made also to determine whether halves or quarters of a 
 fruit, in which the cut surfaces were either covered with vaseline or dried, 
 could be made to take root and form new shoots. This was partially success- 
 ful in only a few instances where part of the piece remained green for a time 
 and some roots were formed, but in no case was a single shoot formed. This 
 was due apparently to the fact that a softening and decay of the exposed pulp 
 of the cut fruit took place, similar to that which occurred in fruits punc- 
 tured for the insertion of cut seeds (see p. 33). 
 
THE FRUIT OF OPUNTIA FULGIDA. 41 
 
 Finally, attempts were made to determine by experiment whether an 
 areole that had once borne a fruit could, after careful removal of this, give 
 rise to a vegetative shoot. When from such fmits all the flowers and sec- 
 ondary fruits Avere removed, and all other areoles cauterized, and the fruits 
 then planted in soil, no shoots at all arose from any of their areoles. This, 
 of course, is rather to be expected, with but a single growing-point in each 
 areole. But the latter condition had not been demonstrated histologically 
 at the time the experiment was initiated. Then, too, it could not be assumed 
 impossible for some of the younger, protected cells from about the margin 
 of an areole of the primary fruit that had already produced a secondary 
 fruit to give rise to a new-shoot growing-point, just as cells outside the areole 
 may initiate a new-root growing-point. In a check experiment 21 fruits 
 that had borne flowers were planted after the removal of these and no areoles 
 cauterized. In 10 months one fruit was dead, 21 were living and rooted, and 
 17 of these bore shoots 3 to 4 cm. high. This demonstrated that no wound 
 injurious to the fruit as a whole is caused by the removal of the secondary 
 flower or fruit. On the other hand, the fact that many of the cauterized 
 fruits mentioned took root and remained green and plump for two years 
 demonstrates that cauterization does not seriously injure the fruit as a whole. 
 
 CAUSES AND SIGNIFICANCE OF PERENNATION AND OF THE 
 DIVERSE TYPES OF PROLIFERATION. 
 
 We have described above the unusual persistence and secondary growth of 
 the fruits of this opuntia and the entirely unique power of the proliferation 
 to flowers and vegetative shoots shown by the areoles of its ovary. Beyond 
 these facts of the structure and habit of fruit and areole lie the physiological 
 problems of the causes and significance in the life-history of these striking 
 peculiarities in this species of Opuntia. 
 
 The primary question to be answered is: Why does the fruit of this 
 cactus never ripen like those of most cacti and of the vast majority of other 
 angiosperms ? ITo appreciable light on this question has been obtained from 
 a study of this opuntia itself. Not a single fruit of this species has been 
 seen, not even an abnormal one, that showed any indication of undergoing 
 those changes which characterize the process of ripening in most other cacti. 
 
 The persistence, year after year, of fruits containing mature ripe seeds in 
 attachment to the parent plant is another peculiarity entirely unexplained 
 by observation thus far made on this opuntia. Dropping off or springing 
 open is in the case of most plants a phenomenon closely associated with the 
 process of ripening. The most noteworthy exception to this general rule is 
 that of Callistemon and allied Myrtaceje investigated by Ewart (1907), 
 where the fruits persist almost indefinitely until killed by the cutting off of 
 the water-supply by fire or drought (fig. 80). 
 
 One possible explanation of the persistent greenness and attachment of 
 the fruit is suggested by the study of an interesting abnormal phenomenon 
 
42 THE FRTJIT OF OPUNTIA FULGIDA. 
 
 observed in certain other Arizona opimtias. The most striking case of those 
 studied is afforded by Opwifia versicolor^ a species in which the normal 
 structure of shoot, flower, and fruit is quite similar to that found in Opuntia 
 fulgida. 
 
 The fruit of 0. versicolor is quite variable in form, size, and habit as to 
 ripening and persistence. It may be nearly globular and from 15 to 20 mm. 
 in diameter, as is true of most of the smaller fruits, or it may be a much-elon- 
 gated structure whose whole length is 4 or 5 times its diameter (figs. 82, 84). 
 These fruits do not soften greatly or change color with the ripening of the 
 seeds, but remain green or yellowish during the autumn and, according to 
 Tourney (1898), usually ripen, wither, and dry up while still on the tree 
 during early winter. Some of the apparently normal fruits, however, as 
 Toumey noted, may remain attached for a year or even two years. This is 
 demonstrated by figures 82, 83, and 86, which were photogi-aphed in late 
 April. 
 
 On examination of large numbers of these plants of Opuntia versicolor in 
 April and May, it was found that most of them (about Y5 per cent) bore no 
 persistent fruits. Of those plants which did bear apparently normal per- 
 sistent fruits, 9 out of 10 bore abnormal gall-like fruits also, of which we 
 shall say more presently. It seems possible then, that the cause of the per- 
 sistence of the normal fruits may be the same as the cause of the abnormality 
 as well as of the persistence of the far more common gall fruits. 
 
 These gall fruits have an exceedingly interesting developmental history. 
 They seem very clearly to be caused by the deposit in the flower-buds of the 
 eggs of the cactus fly {Asphondylia opuntice). These eggs may apparently 
 be deposited at different times in different cases, for the galls show that the 
 flower bud has been arrested and diverted from its normal course at different 
 phases of its development. The galls show that in some cases the arrest of 
 normal development of the flower occurred when the perianth had hardly 
 been initiated, in other cases after the perianth had been half -formed, and 
 in yet others not until the perianth was fully developed (fig. 84, a, h, c, d). 
 
 The degree of disturbance of the normal development of the internal 
 organs of the flower differs markedly. In some cases the stamens, pistils, 
 and even the ovules may have been well started only to become distorted and 
 withered without maturing, while in others no traces of stamens or ovules 
 are te be discovered. Quite independent of these internal features are the 
 size and external form attained by the distorted bud. Sometimes it may be 
 no larger than some normal buds at the time of opening, while again it may 
 reach a length and diameter twice or thrice the normal (fig. 84 a, c). In 
 general external appearance most of these fruits in early April have a plump 
 green ovary and often dark-red, waxy petals. Many of them, in fact, look 
 precisely like gigantic, but otherwise normal flower buds that seem just 
 ready to burst into bloom (fig. 84(i). It is surprising that the petals can 
 persist all winter and retain a color which though darker than the outside of 
 
THE FRUIT OF OPUNTIA FULGIDA. 43 
 
 the petals is not very different from that of the inner surface of the petals in 
 many flowers of this cactus. A section through such an abnormal flower-bud 
 gall taken in April shows from a few to dozens or sometimes scores of the 
 small pupge of Asphondylia within the gall. They are embedded in the 
 cortical region of the ovary, chiefly in the portion above the small ovarian 
 cavity, and they stand perpendicular to the surface of the bud. 
 
 In spite of the rather normal appearance of many of the flower-buds which 
 have wintered over unchanged from the preceding season, they never open to 
 flowers. The nearest approach to this process is found in the curling open 
 of the tips of the petals as the buds finally wither (fig. 81). The only open- 
 ing of these galls that does occur is of quite a different sort. During May, 
 especially in the latter half, the pupse of the cactus fly transform to imagos 
 and break out through the epidermis of the bud, each independently. The 
 pupa-cases are left with half their length projecting beyond the surface of 
 the gall (fig. 81). The fly itself perches on the gall while its wings are 
 hardening (figs. 81, 84), and then flits off to play its part in infecting the 
 new flower-buds of the season, which are then just pushing out of the areoles 
 of the vegetative joints. By the end of May a large share of the emptied 
 galls have withered and dropped to the ground, where they decay, often by 
 the aid of fungi, which have ready entrance about the old pupa cases. 
 
 We come now to the consideration of the possible relation between the 
 gall fruits or gall buds and the apparently persistent fruits. As was stated 
 above, many of these latter fruits contain apparently good seeds. Others 
 have only withered rudiments of seeds, and thus resemble certain of the 
 gall fruits. In fact, a complete series of structures can be discovered 
 grading almost imperceptibly, in both external and internal features, from 
 typical fruits to a persistent normal-appearing flower bud. This, together 
 with the fact that the normal type of persistent fruit in 90 per cent of the 
 cases occurs on plants that also bear gall fraits, suggests that both have a 
 common cause (figs. 82, 84). 
 
 If it is the presence of the egg or larva of Asphondylia or of some sub- 
 stance deposited with the egg that inhibits the normal development of the 
 flower, but stimulates it to an abnormal and locally excessive growth and also 
 causes it to persist over winter, then some lesser amount or degi-ee of this 
 same stimulus may be responsible for the persistence of the apparently nor- 
 mal fruits. Such stimulation might occur either by transmission of some 
 substance or of some stimulus from an infected fruit to a neighboring one, 
 which had not been infected. It is also possible that a fruit which had been 
 bored for the deposit of a single egg, or a few, might continue to develop 
 normally in every respect, except that it persisted on the tree. The only way 
 to distinguish between these two possibilities would be by experimental 
 study. The latter of the two \aewt) stated seems supported by the observed 
 fact that the buds containing most pupa? are generally the ones most modified 
 in structure, while buds or fruits with few pupse are relatively little 
 modified. 
 
44 THE FRUIT OF OPUNTIA FULGIDA. 
 
 In other species, such as the flat- jointed Opimtia discata, the disturbance 
 of the normal development of the flower and fruit hj the laying of the eggs 
 of Asphondylia is never so marked as in Opuntia versicolor. The perianth 
 of this species is always shed, leaving a definite scar. This probably means 
 that it develops to maturity and then opens more or less completely. The 
 general form and size of the resulting fruit are relatively little affected (fig. 
 87). The ripening of the fniit also is only partially inhibited, though the 
 complete ripening and subsequent fall of the fruit are rarely accomplished 
 normally. In one example found at Tucson a fruit of 1913, bearing 50 or 
 more Aspliondylia scars, persisted and bore a vegetative joint 5 cm. long 
 in 1914, and both were plump and green when collected in May 1915. 
 Usually the fly escapes from its pupa-case and the riddled f niit mthers as it 
 does in Opuntia versicolor. 
 
 Griffiths (1913, p. 18) reports that a similar retention of the gall-like 
 flower-buds or fruits in Opuntia puberula is due to the attack of the black 
 opuntia louse. 
 
 If the explanation suggested above for the retention and modification in 
 structure of the flower-buds of Opuntia versicolor is the real one for this 
 case, then it is quite possible that a similar one may be found for the similar 
 peculiarities of 0. fulgida. That is, it is conceivable that some relatively 
 slight change or lack of change in the nature of the cell-sap, or in the char- 
 acter of photosynthetic or other metabolic products of Opuntia fulgida, from 
 a cause as simple as the sting of a fly, though as yet undiscovered, may prove 
 the adequate explanation of the peculiarities of the fruit of this cactus. 
 Experiments have been initiated to test this hypothesis by the aid of injec- 
 tions and by otherwise changing the external or internal conditions affecting 
 the plant. They have not yet been completed. 
 
 We have still to discuss the marked diversity in behavior, under the same 
 conditions, of the different axillary buds of the flower or matured fruit, and 
 also that of the same buds of the fruit under different conditions. If a 
 mature fruit of Opuntia fulgida is taken from the tree at any time from 
 October to April and placed on damp soil, some of its areoles will push out 
 to vegetative shoots. On the other hand, if the same fruit were to be left on 
 the tree till May no shoots at all would be formed, but the same areoles might 
 give rise to flowers instead of vegetative shoots. Moreover, while only the 
 areoles of the distal quarter of the flower or fruit develop so long as the fruit 
 remains attached, any of the buds, except those of the very basal quarter of 
 the fallen fruit, may give rise to root or shoot. The areoles which actually 
 do this are determined by the position of the fruit on the soil. Finally, if 
 these same fruits are taken from the tree about May 1 and planted, the 
 areoles which had already begun to swell slightly do not go on to develop vege- 
 tative shoots, but may either fail altogether to develop or give rise to small, 
 imperfect flower-buds, which soon wither and drop off. Later, other and 
 more basal areoles may proliferate to vegetative shoots. 
 
THE FRUIT OF OPUNTIA FULGIDA. 45 
 
 The questions we have to answer here are these : Why do areoles of fruits 
 that are picked and planted in April give rise, in the follovs^ing month, to 
 nothing but vegetative shoots when if, on the other hand, these fruits were 
 to be left attached till May the same areoles would give rise in that month to 
 flowers, and to these only ? Secondly, what sort of change occurs in the 
 areoles or fruit between April 1 and May 1 which makes the fruit detached 
 at the latter date incapable of doing what it could do if detached at the earlier 
 one ? Thirdly, why do none but the most distal buds of a fruit give rise to 
 flowers, while any but the most basal areoles of a fallen fruit may develop 
 shoots ? 
 
 In regard to the first question, it has occurred to the writer that the 
 attached fruits give rise to flowers because these fruits and their areoles are 
 supplied with substances — perhaps flower-forming substances — which differ 
 markedly from those supplied to the areoles of the same fruit when it has 
 fallen and become rooted in the ground. Or, perhaps the process of root 
 formation may itself produce substances that inhibit flower formation in the 
 same fruit. The plan to experiment on this by rooting attached fruits in 
 pots of soil supported beneath them in the field has not yet been carried out. 
 Several attached vegetative joints of a plant growing in the greenhouse at 
 Baltimore, which from their position seemed likely to produce flowers, were 
 rooted in pots placed beneath them. In the first season, however, these joints 
 developed neither shoots nor fruits. It is planned to repeat this experiment 
 on attached fruits and joints in the field at the first opportimity. 
 
 When a good-sized vegetative joint or two consecutive joints bearing sev- 
 eral fruits is rooted in the soil, these fruits still give rise to shoot-buds only. 
 This is true in spite of the fact that tlie conditions of nutrition here would be 
 expected to be more nearly like those of fruits on a growing plant. 
 
 It was also attempted to discover by experiment whether the production of 
 flowers alone by attached fruits is definitely influenced by the amount and 
 kind of nutritive material available for them, in consequence of their rela- 
 tion to the vegetative branches bearing them and to other fruits. In each of 
 4 plants of Opuntia fulgida several branches were denuded of all fruits 
 except 3 or 4 sets of 1 or 2 fruits each. After three seasons' growth the num- 
 ber of new flowers and fruits that had arisen from these undisturbed fruits 
 was not at all abnoraially increased, nor had the treatment induced the for- 
 mation of a vegetative joint on a single one of the original fruits. The chief 
 tendency of the new growth in these plants was toward the development of 
 new vegetative joints from the old, partially denuded ones. This was most 
 strikingly shown in a tree from which 300 fruits and 100 joints, including 
 the top of the stem, had been lopped off and only two fertile branches with 
 small fruit-clusters left. In this tree the new growth consisted almost 
 entirely of vegetative joints clustered about the cut ends of the main stem 
 and branches. In these cases, therefore, the diversion of all available nutri- 
 
46 THE FETJIT OF OPUNTIA FULGIDA. 
 
 tive material of the vegetative branch into one or two fruits, instead of into 
 several scores, did not change the fate of the areoles on these fmits. There 
 was no increase of the vegetative activity in them such as might have been 
 expected as a result of the increased available food-supply. 
 
 In seeking a reply to the second question proposed on page 45 it was 
 found that all attempts made by planting very young flower-buds to induce 
 these to become metamorphosed into vegetative shoots were unsuccessful. 
 The evidence from these experiments seemed to show that when once tha 
 growing-point of an areole has started, even if but barely started, to form a 
 flower, it can not be diverted and made to give rise to a vegetative shoot, as it 
 could by removing the fruit from the plant and planting it a few weeks 
 earlier. In every case the young flower-bud on a planted fruit either failed 
 to develop at all or developed but slightly and then withered. 
 
 In essential agreement with these results in sprouting the detached fruits 
 are those observed in detached vegetative joints of Opuntia fulgida. Fallen 
 joints, as we have noted, very commonly take root and give rise to new plants. 
 In no case of scores observed were flowers developed from such rooted 
 joints until after a considerable shoot system had been formed. 
 
 In Opuntia vulgaris, however, a series of experiments made in May and 
 June 1917, gave very different results. In practically every case the term- 
 inal joint or pair of joints removed just before the flower buds appear, or 
 just after they are visible, will root promptly and then develop normal flowers 
 and in most cases set fruit (see Hildebrandt, 1888, p. 110). 
 
 The third question raised must apparently be answered by attributing to 
 the influence of polarity the restriction of flower buds to the most distal 
 areoles of the fruit. This is very pronounced so long as the fruit is attached, 
 and is definitely related to the base ; that is, to the point of attachment of the 
 fruit. In fallen fruits a much less definite polarity is exhibited which is 
 determined by the points of origin of roots and new shoots. 
 
 Another problem suggesting itself in connection with the production of 
 flowers from fruits is the discovery of the reason for the fact that only the 
 terminal fruits of a cluster and a few of the subterminal ones give rise to 
 fruits, while all the fruits basal to these, from 1 to 8 or even 10, produce no 
 flowers. This seemed to be equally true whether this basal part of a chain 
 bore one or several secondary or branch chains upon it. In collaboration 
 with Dr. Hermann Spoehr, who planned the chemical side of the work, 
 analyses were made of the pulp of the two basal fruits and the two terminal 
 fruits of each of several chains of six or more fruits. We were unable, how- 
 ever, to discover any difference in the carbohydrates and other nutrient sub- 
 stances present in the distal flower-forming fruits and the basal sterile ones. 
 
THE FRUIT OF OPUNTIA FULGIDA. 47 
 
 PROLIFERATION OF THE FLOWER OR FRUIT 
 IN ALLIED SPECIES. 
 
 The proliferation of the ovarian wall, either in flower or fruit, has been 
 noted in a number of other opimtias, and in at least one other genus, by 
 Engehnaun (1887), Hildebrandt (1888), and a number of more recent 
 workers. (See also, Penzig, 1890, p. 507). Associated with this prolif- 
 eration in certain cases we find a persistence of the fruits for one or more 
 years after maturing. The areoles of the attached fruits of some of these 
 species are known to form flowers only. The attached fruits of others, on 
 the contrary, may develop not only new flowers and fruits, but, under certain 
 conditions, give rise to vegetative shoots also. Of the first type are Opuntia 
 cylindnca, 0. leptocaulis, 0. catacantha, and Peireskia guamacho Rose. 
 Of the second sort are Opuntia rufida, 0. spinosissima , 0. discata, 0. versi- 
 color, and 0. arbuscula. 
 
 Opuntia cylindrica, growing under cultivation but out of doors at Del 
 Monte, California, frequently formed flowers by proliferation from the per- 
 sistent fruits of the previous season (fig. 88). This same species also fur- 
 nished striking examples of the development of first a vegetative joint and 
 then a fruit by the uninterrupted activity of the same growing-point ; that is, 
 the joint and fruit are separated by only a very slight constriction, as was 
 noted in speaking of Opuntia fulgida (cf. figs. 7c^ 88). From the plants of 
 0. cylindrica observed there is no evidence that the primary flowers ever give 
 rise to buds of secondary ones before they are open. 
 
 Opuntia toumeyi, growing near Tucson, may occasionally form secondary 
 flowers close to the base of the primary ones, which open soon after the latter. 
 
 Opuntia leptocaulis is a slender Arizona species, growing along with 0. 
 fulgida, in which fruits may persist unripened or half-ripened and then 
 bud out new flowers in the succeeding season (fig. 89, a, h, c). These pri- 
 mary fruits may persist for a year and a half and the secondary ones may 
 ripen, but tertiary fruits are rarely formed. The propagative structures 
 here show a very closely graded series of intenuediatc forms between the 
 typical fruit and the vegetative joint, a series far more complete than can 
 usually be found on 0. fulgida or any other near Tucson. One plant of 0. 
 leptocaulis seen at Chico in August bore numerous slender vegetative 
 joints on persistent fruits of the same season and also of the preceding season. 
 
 The graded series of propagative structures above mentioned contains 
 typical obovate fruits, with definite perianth-scars, evidently fonned by nor- 
 mally opened flowers. Other fruits are twice as long, but still show the scar 
 of a normal perianth. Then there are joints of various lengihs, of wliich 
 some bear small or very small perianth-scars while others have no scars at 
 all, and yet all of them look very fruit-like in other external aspects. There, 
 are also many slender joints having no perianth-scars, yet closely resembling 
 the more slender sterile fruits that do have them, l^one of these various 
 structures except the shorter, obovoid ones may contain seeds, and some even 
 
48 THE FRUIT OF OPUNTIA FULGIDA. 
 
 of these are seedless. Any of the sterile, fruit-like bodies may be easily dis- 
 lodged and on moist ground their areoles may give rise to new plants. Such 
 a complete series of more or less fruit-like structures might easily give the 
 impression that these sterile propagules have arisen phylogenetically by the 
 progressive sterilization of the normal type of fruit, accompanied by an 
 increase in its povt^er of sprouting from its areoles until the sterile fruits 
 have become the chief propagative structures of this species. The plausi- 
 bility of this view we shall consider in detail later (p. 52). In the mean- 
 time, however, we must remember that the so-called fruit of these opuntias 
 is made up largely of purely vegetative elements, the internodes and the 
 areoles and their products. It is clearly for this reason that many sterile ova- 
 ries, such as in other angiosperms (where they occur commonly) would soon 
 wither and fall, may in Opuntia persist as essentially vegetative structures. 
 
 Opuntia catacantha {0. rubescens Salm-Dyck) is a West Indian species 
 resembling 0. fulgida in certain respects more closely than any other opuntia 
 studied. It is tree-like, with very flat, paddle-shaped or scimitar-shaped 
 joints, which in the variety studied are without spines. The fruits persist 
 from one season to the next and then bear primary flowers of the latter sea- 
 son. These may bear secondary flowers and the latter form tertiary ones, 
 and thus chains of fruits consisting of at least 6 or 8 links may finally be 
 formed (fig. 90). These fruits vary in size, form, and internal structure. 
 The flowers and young fruits are slender and obconical or sometimes slightly 
 bent (fig. 90). As the fruits mature they increase considerably in size, 
 often to about twice the original length (50 to 60 mm.) and to 4 or 5 times 
 their original thickness. Mature fruits are often flattened until only half as 
 thick on one transverse axis as on the other (lY by 30 mm. for example, in 
 one sho\ATi in fig. 9). Few of the fruits have fertile seeds. 'None of those 
 dissected by the writer had good seeds, but a few ripe seeds were sent him 
 by a correspondent, the Rev. A. B. Romig, of St. Thomas, Virgin Islands. 
 
 The seed remnants found are of various sizes up to about half-growm seeds, 
 but all are brown and withered. No definite information is available 
 regarding the ability of these fruits to sprout to new shoots, but the fact that 
 they are nearly always sterile suggests that they may serve as propagules just 
 as the fruits of 0. fulgida do. This possibility is rendered more plausible by 
 the fact that in another spiny variety of Opuntia catacantha (0. monili- 
 formis Haworth) collected on Mona Islands, near Haiti, by Dr. N". L. Brit- 
 ton, chains of short joints 1.5 by 3' cm. long are formed, which are said to 
 sprout to new plants. These are spiny and except in size are like the regular 
 vegetative joints. They are not pseudo-fruits like those described in 0. 
 leptocaulis. 
 
 In PeiresJcia guamacho is found the most striking case of proliferation of 
 the flower that has been seen outside the genus Opuntia, and it appears the 
 more remarkable because of the large bracts and long stalks of the successive 
 flowers. In this species, as it grows in greenhouses in Washington, each 
 
THE FRUIT OF OPUNTIA FULGIDA. 49 
 
 flower usually bears 4 bracts and each of these has a secondary flower in its 
 axil. The stalks of a secondary flower may get to be a centimeter long or 
 more and this gives the flower-cluster quite a different appearance from that 
 of an opuntia, though its general plan is the same (figs. 92, 93). One or 
 two, rarely more, of the flowers in such a group may develop fruits (cf., 
 Delavaud, 1858). Each globular, fleshy fruit bears a well-defined areole 
 above each bract-scar and usually contains from one to several large, flat 
 seeds. These seeds germinate readily, but all attempts to induce the areoles 
 of a detached, unripened fruit to proliferate to a shoot failed. No case of 
 the vegetative proliferation of the areole of a fruit was observed. In a 
 similar species of Peireskia growing at Chico, a single parent fruit some- 
 times bore 5 secondary fruits and the basal secondary ones not uncommonly 
 bore in turn tertiary fruits ; that is, three generations of fruits were formed 
 in a single season. 
 
 In the second series of species mentioned on page 47 the attached friiit 
 sometimes proliferates to form vegetative joints as well as to give rise to 
 flower buds. All but one of these opuntias resemble 0. fulgida in that they 
 form these vegetative shoots only rarely. Thus, in the flat-jointed species, 
 Opuntia rufida, from Doctor Rose's collection in Washington, in 0. spinosis- 
 sima from Jamaica, and in 0. discata, studied in the field at Tucson, the 
 development of vegetative shoots from attached fruits occurred very infre- 
 quently (fig. 94). Hildebrandt (1888, p. 112) has reported such a case in a 
 flat-jointed Opuntia gro\\dng in Freiburg. He attributed this imusual 
 behavior to exceptionally good nutrition of the cultivated specimens. Pro- 
 liferation of the fruits I foimd not at all uncommon in a number of the 
 above-mentioned opuntias, and of other flat opuntias growing in the collec- 
 tion of Doctor Griffiths, at Chico, California {cf. Griffiths, 1913). In the 
 cylindrical species, 0. versicolor, the occurrence of such a proliferation of 
 the attached fruit to vegetative joints is relatively very rare, only 3 or 4 cases 
 being seen in hundreds of plants examined. In two at least of the three 
 cases of this tjq^e observed the proliferating fruit was evidently a gall fruit 
 (fig. 85 ) . This fact of itself proves that these gall fruits do not always drop 
 off during the second spring. It is doubtful, however, if they are capable, 
 except in the rarest instances, of holding on long enough to make their vegeta- 
 tive offshoots an important part of the branch system. The irregularity in 
 branching, usually resulting from proliferation of a gall fruit to a branch, 
 should make this phenomenon discoverable several years after its occurrence 
 (figs. 85, 86). No certain cases could be found, however, that indicated 
 clearly the persistence of such a fruit-borne branch for more than a year or 
 two. This sort of proliferation is practically identical with that occurring 
 so rarely in Opuntia fulgida, except that in the latter the proliferating fruit 
 is in other res])ects often a normal one. 
 
 On the contrary, in the round-jointed Opuntia arhuscula, the proliferation 
 of attached fruits to form vegetative shoots is, under some conditions at least, 
 4 
 
50 THE FEUIT OF OPUNTIA FULGIDA. 
 
 not a rarity, but a very common occurrence. The fruit of this species is per- 
 sistently green, shows no sign of ripening, and not more than 5 per cent of 
 them have well-ripened seeds. This fruit is pear-shaped, rather slender, 
 smooth, and spineless, like that of 0. fulgida, and has rather prominent 
 areoles. The areoles of the primary flower very often proliferate to secon- 
 dary flowers and the fruits commonly persist over one or more winters. Most 
 of the persistent fruits are single, but chains of two are common and chains of 
 3 or 4 links are not infrequent. The fruits of the upper part of the rather 
 bush-like plant seem always to produce only flowers so long as they remain 
 attached. Many of the fruits of the lower branches, however, often give rise, 
 from one or more up to 6 or 8 of the distal areoles, to rather slender, con- 
 densed branches, bearing numerous prominent areoles ( fig, 95 ) . These con- 
 densed branches, which may also arise on vegetative joints, are vertical in 
 position, are about 4 or 5 mm. in diameter, and 20 to 50 mm. long. If these 
 short branches are left on the plant they may thicken somewhat and become 
 more like the normal, terete, vegetative shoots. ISTo evidence was obtained, 
 however, that the persistent fruit and its vegetative offshoot ever become 
 incorporated into the permanent branch system of the parent plant. These 
 condensed branches apparently play no important part in the development of 
 this opuntia, except when the fruits or the branches alone fall to the ground, 
 there to take root and thus start new plants. 
 
 Wliat has been said of the proliferation of the fruits in the various 
 Opuntias and in Peireskia indicates that each is peculiar in its own way in 
 regard to the ripening of the fruit, in its persistence, and its proliferation to 
 flowers or to vegetative shoots. 
 
 In the first place, the fruits of two species, 0. arhuscula and 0. catacantha, 
 have fruits resembling those of 0. fulgida in that they normally fail 
 to ripen. The other four species, 0. cylindrica, 0. leptocaulis, 0. rufida, 
 and 0. versicolor, apparently fail to ripen only because of some unusual 
 condition within or about them. 
 
 Secondly, of the .eight species of Opuntia just mentioned only two, 0. 
 arhuscula and 0. catacantha, seem to resemble 0. fidgida in having normally 
 persistent fruits. In the others this is the less usual thing, due in all cases 
 perhaps, as it evidently is in 0. versicolor, to some unusual cause, such as the 
 stimulus caused by Asphondylia. There are many other species also in 
 which, as was noted by Griffiths (1913), the abnormal conditions of growth 
 provided in cultivation frequently induce persistence of the fruits. 
 
 Thirdly, the proliferation of the areoles of the ovary to flowers, while 
 apparently a nonnal occurrence in 0. arhuscula, 0. catacantha, and the 
 closely related 0. spinosissima, as it also is in 0. fulgida and Peireskia, is 
 a rarer phenomenon in the other four species mentioned, and in them occurs, 
 usually, if not always, under abnormal conditions. 
 
 Finally, the proliferation of the areoles of fallen fruits to roots and shoots, 
 thus to form new plants, may apparently occur in any of the seven opuntias, 
 but not in the soft, quickly ripening fruits of Peireshia. 
 
THE FRUIT OF OFUNTIA FULGIDA. 51 
 
 Taking into account all four of the peculiarities mentioned, it is clear that 
 Opimtia fulgida is, on the whole, the most generally peculiar type studied, 
 followed most closely perhaps by 0. arhuscula and 0. catacantha. At the 
 other end of the graded series is Opuntia versicolor, which behaves like a 
 normal angiosperm in most, or perhaps all, cases where it is not stimulated 
 by the cactus fly, Aspliondylia. 
 
 It is evident (from observations made in Arizona, in the cactus garden 
 of the Bureau of Plant Industry established by Doctor Griffiths at Chico, 
 and from records in the literature, of cases such as Opuntia prolifera, 
 0. cJiolla, 0. spinodor, etc.) that many other species of Opuntia fit in at 
 various points in the series described above. In other words, in the genus 
 Opuntia the ovary, in flower and in fruit, may assume now more, now fewer 
 of the various functions of the vegetative joint. Of the Opuntia fruits thus 
 far studied from this point of view, that of Opuntia fulgida seems not only 
 the most atypical angiospemious fruit among these Cactacea?, but is perhaps 
 also the most aberrant (shoot-like) fruit to be found in all angiosperms. 
 
 PROLIFERATION OF JOINTS AND FRUITS IN 
 RELATION TO THE STERILITY OF FRUITS. 
 
 From what has been said above of Opuntia fulgida it is evident that the 
 propagation of this cactus has ceased to depend chiefly on the development of 
 fertile seeds, and so of seedlings, but is accomplished more largely by the 
 vegetatix-e sprouting of fallen joints and of fallen fruits. The propagation 
 of the species by the rooting of joints or parts of joints is rather common in 
 several genera of Cactacea?, such as Cereus, Mammillaria (Goebel, 1889), 
 Peircslda, etc., in addition to many and probably most species of Opuntia. 
 The propagation by means of the fallen fniit is probably common among 
 opuntias with persistent fruits. Besides its occurrence in the forms already 
 mentioned, it is apparently common also in 0. prolifera, 0. cholla, 0. 
 spinosior, etc. 
 
 In a number of other opuntias and certain other genera there are devel- 
 oped, in addition to the true fruits and ordinary vegetative joints, more 
 specialized short joints which are often bead-like or more or less fruit-like in 
 character. These occur, for example, in 0. arhuscula, 0. catacantha, 
 0. fulgida, 0. leptocaulis, 0. tetracantha (Toimiey, 1905), Mammillaria 
 gracilis (Goebel, 1889), a species of Cereus, etc. In each case these struc- 
 tures are capable, after falling, of taking root in the soil and tlius starting 
 new plants. 
 
 Taking this whole series of structures, together with the various sorts of 
 joint fruits that occur in 0. fuJgida and many other opuntias, and the many 
 seedless opuntia fruits, it might be assumed that the fruit of these Cactacefe, 
 and especially of the opuntias, is losing its primary function of seed-produc- 
 tion. ^ It is evident at least that the production of new plantlets and the 
 function of dissemination has been taken over in large part by these various 
 
52 THE FRUIT OF OPUNTIA FULGIDA. 
 
 vegetative propagating bodies. This raises the question whether the seed- 
 bearing fruit of all opuntias is on the way to extinction, through a progres- 
 sive loss of the seed-bearing function, which may be expected to end in the 
 evolution of a totally sterile fruit, having no propagative functions other 
 than those that can be equally performed by vegetative joints. 
 
 It is true that the vegetative joints and both the fertile and sterile fruits 
 resemble each other greatly in their capacity for proliferation. There seems 
 no adequate reason, however, for assuming that either the proliferating habit 
 or the fundamental structure of the fruit is a secondary thing in the evolution 
 of the opuntias (Toumey, 1895). On the contrary, it is natural that the 
 thick-skinned, water-stored joints of these cacti should prove capable of per- 
 sisting on moderately moist soil until rooted deeply enough to secure a water- 
 supply adequate for the starting of a young plant. The fruit being, as we 
 have seen, really a stem in organization, up to the latest phase of its develop- 
 ment, it is also very naturally capable of proliferatiou to root and shoot. 
 The capacity of joint and fruit for persistence and proliferation is probably 
 as old as the fleshy character of the family. The persistence of the sterile 
 fruits, at least to maturity, is not a really surprising thing, in view of the 
 preponderatingly vegetative and stem-like character of the bulk of the wall 
 of the ovary. Sterile ovaries occur in many species of angiosperms, but in 
 most of these the carpels constitute the bulk of the fruit. Therefore, when 
 the seeds are wanting in these forms, and the carpels as usual fail to develop, 
 no fruit is formed and the flower bud soon withers and drops off. In 
 Opuntia, on the contrary, even if the seeds and carpellary portion of the 
 fruit do fail to develop, the basal stem-like part may go on, practically 
 unhindered in its vegetative growth, and mature quite normally. 
 
 When these facts concerning the comparative structure and behavior of the 
 stem and ovary of Opuntia are considered, in conjunction with the fact that 
 leaves are present on both and with the undoubted similarity of Opuntia to 
 Peireskia, there seems no adequate reason for believing that the fniit of 
 Opuntia is, structurally, an advanced type among the Cactacese. On the 
 contrary, Opuntia and its close relative Peireskia (which also has a leafy 
 ovary, the areoles of which, in the flower, proliferate to secondary flowers) 
 probably show us the simplest type of the inferior (submerged) ovary char- 
 acteristic of the Cactaceae. The capacity of the Opuntia fruit for persistence 
 and proliferation is to be regarded as the natural outcome of its original 
 morphological composition — i. e., a joint with an ovary immersed in its apex. 
 It seems clearly not a result of a marked degeneration of a once less stem- 
 like and more constantly fertile fruit, such as has been assumed ])y some 
 investigators to have been present during the evolution of the genus. The 
 more specialized or highly evolved flowers and fruits, structurally, among the 
 Cactacese are probably to be sought in such genera as Cereus, Rhipsalis, and 
 Mammillaria. 
 
THE FEUIT OF OPUNTIA FULGIDA. 53 
 
 SUMMARY AND CONCLUSIONS. 
 
 The fruits of certain opuntias differ from those of other angiosperms, 
 except those of some Australian " bottle-bnish " trees, in not ripening and 
 then either opening or falling from the plant when the seeds are mature. 
 On the contrary, the peculiar fruits of these Cactacese and MyrtacesG remain 
 attached to the plant and actively growing for several or many years. 
 
 The persistent fruit of Opuntia fulgida is still more abnormal in another 
 respect, for it not only remains attached, unripened and steadily growing, 
 season after season, but the seeds are never shed from the fruit. Further- 
 more, the matured fruit itself, or even the ovary of the unopened flower, 
 while still attached to the tree, may give rise to secondary flowers and so to 
 other fruits. Four or five generations of flowers and fruits may thus be 
 formed in a single season. Finally, if a mature fruit falls on moist soil it 
 may develop adventitious roots and shoots and thus initiate a new plant. 
 
 This tree-like opuntia has a tuberculate and spiny cylindrical stem and 
 branches, the fleshy joints of which on separation readily sprout to new 
 plants. 
 
 The early development of the ovary of the flower in Opuntia fulgida 
 closely resembles that of a young vegetative joint, and the structure resulting 
 from this early development, with its minute, evanescent leaves, its tubercles, 
 and axillary areoles, is entirely stem-like in appearance. Only with the 
 initiation of the perianth, stamens, and carpels does the fertile joint become 
 distinctly flower-like in character. The ovarian cavity finally becomes com- 
 pletely buried in the stem-like, basal portion of the ovary, by the more rapid 
 growth of this portion upward and inward about the base of the carpels. 
 The whole outer wall of the ovary and fruit is thus a stem in its morpho- 
 logical origin. This is clearly indicated not only by the more general fea- 
 tures of development noted, but also by the identity in details of development 
 and structure of the tubercles and areoles, and of the photosynthetic and 
 water-storing tissues in the stem and fruit. In its physiological capacity 
 for persistence and for proliferation to flowers and shoots, the wall of the 
 fruit shows again its essential identity with the stem. Finally, the graded 
 series of structures intermediate in character between joint and fruit, sen-e 
 to further emphasize the likeness of the two. 
 
 The development of the flower of this opuntia indicates that it has evolved 
 from one with an originally superior ovary through the progressive submer- 
 gence of this ovary by the more vigorous growth of parts of the fertile joint 
 that were laid down before the carpels themselves were even initiated. Tliis 
 is probably a relatively primitive type of flower among the Cactacese, from 
 which the type found in Cereus and Echinocactus has been derived. 
 
 The perianth, the stamens, and the style are cut off from the top of the 
 ovary, a day or two after the flower withers, by the formation of a highly 
 developed, cup-shaped abscission layer. Any cells of the fruit except those 
 
54 THE FRUIT OF OPUNTIA FULGIDA. 
 
 of the vascular bundle may participate in the formation of the cells of the 
 abscission layer. The cells of the vascular bundle in line with the abscission 
 layer seem to degenerate and rupture as a result of the split in the adjoining 
 tissues. The whole funnel-like scar left at the top of the ovary by the fall of 
 the perianth is soon protected by several layers of periderm. These arise 
 from a phellogen formed but a few layers within the abscission layer. One, 
 or sometimes several, layers of this periderm may have the cell-walls greatly 
 thickened to form a schlerenchymatous protective layer. 
 
 From the axillary buds, or areoles, of the primary flowers that open in 
 May, arise secondary flowers which open in June. From areoles of these, in 
 turn, tertiary flowers open in July, and on the latter quaternary flowers 
 bloom forth in August. Thus four and sometimes five generations of flowers 
 may be formed each season. Often two or three and sometimes four genera- 
 tions of persistent fruits may thus arise in a single summer. 
 
 The number of well-matured seeds occurring in a fruit may range from 
 to 100 or even 200. Large numbers of sterile seed-rudiments of various 
 sizes are found in most fruits, some of them evidently having degenerated 
 soon after their initiation. The fertile seed contains a large coiled embryo 
 and a small mass of endosperm in the loop between radicle and cotyledons. 
 The seeds of this opuntia have not, so far as is recorded, been Icnown to ger- 
 minate in the field under natural conditions. They were germinated in the 
 laboratory by slightly chipping the seed-coat. The seeds may remain 
 unchanged and capable of germination for several or many years while 
 embedded in the pulp of the persistent, attached fruits, or even in that of 
 fallen, rooted ones. The seeds are set free in nature only by the decay of 
 the pulp of the fallen fruit, or when the fruits are eaten by browsing animals. 
 It is possible that the failure of the seeds to germinate in the moist pulp of 
 the fruit, even during the hot summer, may be due to the impenetrability of 
 the seed-coat. Even chipped seeds, however, do not germinate in this 
 medium as they do in soil or on wet filter-paper, which suggests that the pulp 
 may have an inhibitory effect on some process connected with germination. 
 
 The mature fruit, unripened, remains attached to the tree after the ripen- 
 ing of the seeds. It may thus persist and grow year after year, by the aid 
 of a cambium ring. It is this persistent fruit that gives rise to flowers, just 
 as a stem would. By the proliferation of the primary flowers, so formed, 
 secondary and tertiary flowers arise and develop to persistent fruits, two, 
 three, or even four generations per season. In the course of several years a 
 cluster may arise containing scores of fruits with sometimes 10, 12, or even 
 14 generations of fruits in a continuous linear series. 
 
 Only in two cases, among hundreds examined, were attached fruits found 
 proliferating to vegetative joints. 
 
 Fallen fruits that rest on moist ground may give rise to adventitious roots, 
 from areoles, perianth-scar, or stalk-scar, and then to vegetative shoots, from 
 areoles only, and thus initiate new individual plants. In nature this origin 
 
THE FRUIT OF OPUNTIA FULGIDA. 55 
 
 of new plants from fallen fruits is the most important means, next to prolif- 
 eration of fallen joints, of the multiplication and dispersal of this cactus. 
 
 The difference between the product of an areole of an attached fruit and 
 one of a fallen fruit that has rooted seems probably due to a difference in the 
 kind of nutritive (organ-building) material brought to the two areoles under 
 these different conditions. It is possible that the presence of roots on the 
 fallen fruit inhibits the formation of flowers by it. 
 
 Persistence and proliferation of the fruit, though not elsewhere as fre- 
 quent as in Opuntm fulgida, is not unknoA\Ti in other species. In Opuntia 
 versicolor, as also in several flat-jointed opuntias, the frequent persistence of 
 the fruit or even of the unopened flower is the result of the puncture of the 
 flower-bud by the cactus fly, which lays its eggs in it. In other cases, like 0. 
 catacantha, the factors that inhibit ripening and induce persistence are as 
 undetermined as they are in the case of 0. fulgida. 
 
 The fact that Opuntia fulgida and other species have series of fruits show- 
 ing various degrees of sterility, from those with scores of seeds to those that 
 are entirely seedless, can not be taken as conclusive evidence that seed-produc- 
 tion is really on the way to complete extinction in these plants. ISTeither is 
 the corollary that propagation by seeds is being replaced by the proliferation 
 to new plants of fallen fruits as significant as it might at first seem. On the 
 contrary, the stem-like character of the fruits in this genus results in the per- 
 sistence of many sterile ovaries, such as would, in many less fleshy angio- 
 sperms, wither and fall off soon after blooming, instead of maturing into 
 seedless fruits, as they do here. 
 
56 THE FRUIT OF OPUNTIA FULGIDA. 
 
 LITERATURE CITED. 
 
 Caspaei, H. 1883. Beitrage der Kenntniss des Hautgewebes der Cacteen. Zeit. 
 
 fur Naturwiss., 2, pp. 30-80. 
 Cbockeb, W. 1906. Role of Seed-coats in Delayed Germination. Bot. Gaz., 42, pp. 
 
 265-290. 
 Daebishire, O. V. 1904. Observations on Mammillaria elongata. Ann. of Bot., 18, 
 
 pp. 375-416. 
 Debet, M. H. 1846. Proliferation d. Fruchtknotens lieferte eine Opuntia Salm- 
 
 Dyckiana. Verhandl. d. Naturhist. Ver. Preuss. Rheinl., 3, 83, 84. 
 Delavaud, M. C. 1858. Inflorescence du Peireshia bleo. Bull. Soc. Bot. de France, 
 
 5, p. 685. 
 Delbbouck, C. 1875. Die Pfianzenstacheln. Hanstein Botan., Abhandl. 2, pp. 1-119. 
 Engelmann, W. 1887. " Cactacese of the Boundary," in Botanical Works. Edited 
 
 by W. Trelease and Asa Gray. Cambridge, p. 212. 
 EwAET, A. J. 1907. The Delayed Dehiscence of CalUstemon rigida. Ann. of Bot, 21, 
 
 pp. 125-137. 
 Ganong, W. F. 1894. Beitrage zur Kenntniss der Morphologie und Biologic der 
 
 Cacteen. Flora, Erganzungsb., pp. 49-86. 
 . 1898. The Comparative Morphology of the Embryos and Seedlings of the 
 
 Cactace*. Ann. of Bot., 12, pp. 423-474. 
 GOEBEL, Karl. 1886. Zur Entwickelungsgeschichte des Unterstandigen Frucht- 
 knotens. Bot. Zeit, 44, pp. 729-738. 
 
 . 1889. Pflanzenbiologischeschilderungen. I. Kakteen, pp. 67-108. 
 
 Griffiths, D. 1913. Behavior, Under Cultural Conditions, of Species of Cacti 
 
 Known as Opuntia. Bull. No. 31, U. S. Depart, of Agricult. 
 Harris, J. A. 1905. The Fruit of Opuntia. Bull. Torrey Bot. Club, 32, pp. 531-536. 
 HiLDEBRANDT, F. 1888. Ueber Bildung von Laubsprossen aus Bliithensprossen bei 
 
 Opuntia. Ber. d. deutsch. bot. Gesellsch. 6, pp. 109-112. 
 Kauffmann, N. 1859. Zur Entwickelungs. d. Cactaceenstacheln. Bull. Soc. Imp. 
 
 des Naturalistes de Moscow, 32, part II, pp. 585-603. 
 Lauteebach, C. "W. 1889. Untersuchungen iiber Bau und Entwickelungs der Sekret- 
 
 behalter bei des Cacteen. Bot. Centrbl., 37, p. 257. 
 Lloyd, F. E. 1907. Observations on the Flowering Period of Certain Cacti. Plant 
 
 World, 10, pp. 31-39. 
 
 . 1916. Abscission in MiraUlis jalapa. Bot Gaz., 61, pp. 213-230. 
 
 Meehan, T. 1888. Opuntia Fruits. Gard. Chron., 3, p. 328. 
 
 Noll, F. C. 1872. Zwei Abnormitaten an Cactusfruchten. Ber. d. Senckenbg. 
 
 Gesell., 1872, p. 118. 
 Penzig, 0. 1890. Pflanzenteratologie. Genoa. 
 Schleiden, M. J. 1845. Beitrage zur Anatomie des Cacteen. Mem. I'Acad. Imp. d. 
 
 Sci. d. St Petersb., ser. 6, vol. 4, pp. 335-380. 
 Schumann, K. 1894. " Cactacese." Engler u. Prantl, III, Qa, pp. 156-205. 
 
 . 1890. Flora Brasiliensis, IV, 2. 
 
 SoLEREDER, H. 1908. Systematic Anatomy of the Dicotyledons. Engl. Transl., pp. 
 
 406-415. 
 TouMEY, J. W. 1895. Vegetal Dissemination in Opuntia. Bot. Gaz., 20, pp. 356-361. 
 
 — . 1898. The Tree Opuntias of the United States. Bot. Gaz., 25, pp. 119-124. 
 
 . 1905. Notes on the Fruits of Some Species of Opuntia. Bull. Torr. Bot. 
 
 Club, 32, pp. 235-239. 
 Wettebwald, X. 1889. Blatt- und Sprossbildung bei Euphorbien und Cacteen. 
 
 Nova Acta Kaiserl. Leopold. Carol., Ak. 53, pp. 379-440. 
 Wolfe, F. A. 1912. Notes of the Anatomy of Opuntia lindheimeri. Plant World, 
 
 15, pp. 294-298. 
 ZuccABiNi, J. G. 1836. Plantarum novarum vel minus cognitarum, etc. Fasc. 
 
 tertius, Cactacese. Abhandl. Muench. Akad., Math, physik. Klasse, 2, 
 
 pp. 599-742. 
 
THE FRUIT OF OPUNTIA FULGIDA. 57 
 
 EXPLANATION OF PLATES. 
 
 ABBREVIATIONS USED IN PLATES. 
 
 a., areole or cushion formed by axillary bud; a. I., abscission layer; &., bristle or 
 glochidium ; bb., barb of bristle or of spine; c, carpel; ck., cork; cm., cambium; 
 c. c, crystal containing cell; c. t., conducting tissue of style; c. to., cell-wall; c, epi- 
 dermis; em., embryo; ep., endosperm; /., flower; fu., funiculus or stalk of ovule; 
 g. c, guard-cell; g. p., growing-point; h., hypodermis; i., integument; I., leaf; l. s., leaf- 
 scar; n., nectary; o., ovary; ov., ovule; p., petal; ph., phellogen; pi., palisade; p. s., 
 perianth-scar; r., root; s., sepal; sa., stamen; s. c, slime-cell; sd., seed; sg., stigma; 
 sh., sheath of spine; so., stoma; sp., spine; st., stem; sy., style; t., trichome; tb., 
 tubercle; v. b., vascular bundle; w. f. wall of fruit. 
 
 Frontispiece. 
 Photograph of a mature plant of Opuntia fulgida on reservation of Desert Laboratory 
 at Tucson, showing a frequent type of forked trunk, due to injury of main 
 axis, also the branching habit and clusters of fruit. The nesting bird is the 
 cactus wren, Heleodytes brunneicapillus couesi (Sharpe). [D. T. MacDougal 
 photo.] 
 
 Plate 1. Photographs of Opuntia fulgida. 
 
 Fig. 1. A fruiting plant growing in the desert at Tucson. Photographed April 25, 
 1915. X 0.03. 
 
 Fig. 2. Heavily fruiting branches of a tree on the campus of the University of Arizona. 
 The largest cluster included more than 100 fruits. Photographed in 
 May 1912. X 0.1. 
 
 Fig. 3. A single large cluster of fruits from the same tree as figure 2. X 0.3. 
 
 Fig. 4. A vegetative joint and fruits of 1914 bearing buds of flowers of 1915. Photo- 
 graphed in May 1915. X 0.6. 
 
 Plate 2. Photographs of 0. fulgida. 
 
 Fig. 5. Tip of a vegetative joint with young joints still bearing the evanescent leaves, 
 showing also areoles with spines and nectaries. X 0.9. 
 
 Fig. 6. Four generations of flowers and fruits developed from a vegetative joint in the 
 season of 1915. This cluster, collected at Tucson and photographed in 
 mid-July 1915, shows the relative sizes of the four generations. No. I 
 opened in May; II in June; III, if not removed from the plant, would 
 have opened in late July; IV in late August. Note that some members 
 of generation III (at right below) have but barely pushed out of the 
 areole. X 0.6. 
 
 Fig. 7 a, b, c. Joint-fruits and pseudo-fruits, showing several structures combining in 
 various degrees the characters of vegetative joint and fruit. X 0.45. 
 
 Fig. 8. Cluster of 11 secondary fruits borne on a single primary fruit showing the 
 persistence of fruits over one, two, or more winters. Photographed 
 April 1915. X 1. 
 
 Fig. 9a. Joint of 1914 bearing opened and withered flower of 1915, the latter with 
 buds of secondary flowers on its sides. X 0.6. 
 
 FiQ. 9&. Similar joint bearing primary flowers. In the areoles of these are borne 
 trichomes, nectaries, and buds of secondary flowers. Many of the latter 
 bear numbers of the awl-shaped deciduous leaves. X 0.6. 
 
 Plate 3. Drawings of O. fulgida. 
 
 Fig. 10. Radial section of an axillary bud of flower, showing growing-point, nectary, 
 
 spine, etc. X 25. 
 Fig. 11. Longitudinal section of a flower bud through a placenta, mammillae, leaves, 
 
 two axillary buds, a nectary, etc. X 3.33. 
 
58 THE FRUIT OF OPUNTIA FULGIDA. 
 
 Fig. 12. Enlarged drawing of the areola shown at left in figure 11. It would probably 
 have developed a flower if it had been left on the plant. X 25. 
 
 Fig. 1.3. Part of a longitudinal and radial section of an unopened flower, bearing the 
 very young bud of a secondary flower at right. X 5. 
 
 Fig. 14. Longitudinal section of a young flower bud arising from the edge of the 
 perianth-scar on the fruit of the preceding season, showing leaves, very 
 prominent tubercles, and growing-points of the areoles on the adaxial 
 faces of the latter; showing also the shriveled nectaries developed in the 
 preceding season. X 12. 
 
 Fig. 15. Longitudinal section of a slightly older flower than that shown in figure 14, 
 showing the depression of the growing-point and the initiation of the 
 stamens. X 18. 
 
 Fig. 16. Longitudinal section of a still more advanced flower, showing the much 
 sunken growing-point and three series of stamens on each side of it. 
 X 18. 
 
 Fig. 17. Longitudinal section of flower with all stamens and carpels initiated. The 
 two upper areoles now face upward instead of axially. X 9. 
 
 Fig. 18. Part of a longitudinal section of a young flower showing further closing in of 
 the carpels above the cavity of ovary to form stylar canal. X 24. 
 
 Fig. 19. Longitudinal section of upper part of a slightly older flower, showing style 
 with free tips that are to form stigmas. X 17. 
 
 Fig. 20. A section, similar to that in figure 19, of a flower in which the placentae are 
 just distinguishable; at base of nectary at left is a leaf-scar, and below 
 the nectary is the vascular bundle that led to leaf. X 8. 
 
 Fig. 21. Longitudinal section of a half-matured flower, showing ovules just initiated, 
 stamens differentiated to anther and filament, etc. X 5. 
 
 Fig. 22. Longitudinal section of a flower nearly ready to open, showing ovules, style 
 with its conducting tissue, the papillose stigmas, and tightly over- 
 lapped sepals and petals. X 4.5. 
 
 Plate 4. Drawings of 0. fulgida. 
 
 Fig. 23. Longitudinal section of a flower that has just commenced to open, showing 
 
 ovules, papillose recurved stigma-lobes, etc. X 4. 
 Fig. 24. Longitudinal section of a young fruit from which the perianth and stamens 
 
 have recently fallen, showing the funnel-shaped scar with its corky 
 
 lining layer. X 3. 
 Fig. 25. Longitudinal section of a primary fruit with ripe seeds bearing a secondary 
 
 fruit, showing relative size of fruits and degree of development of seeds, 
 
 the connection of vascular systems, etc. X 1.5. 
 Fig. 26. Longitudinal section of two matured fruits, one or two years old, with 
 
 aborted seeds of various sizes, though fruits are plump and normal in 
 
 external form. X 1.25. 
 Fig. 27. Longitudinal section of a mature fruit, showing the usual shape of fruit, its 
 
 perianth-scar, areoles, and vascular system, also ripe seeds, together with 
 
 other seeds that have withered at various stages of development. X 1.25. 
 Fig. 28. Longitudinal section of a combination joint fruit, one or two years old, 
 
 showing the relatively small portion of its length occupied by the 
 
 ovarian cavity, which in this case contained only half-matured withered 
 
 seeds; showing also the vascular system and the prominent tubercles, 
 
 the one at the right with two spines. X 1.5. 
 Fig. 29. Transverse section of young flower bud showing petals, sepals, leaves, and at 
 
 left one spine. X 10. 
 Fig. 30. Transverse section of same bud lower down, showing the six stigmas, petals, 
 
 sepals, leaves, and the very prominent tubercles with their areoles; 
 
 showing nectaries, spicules, etc. X 5. 
 Fig. 31. Transverse section of the bud shown in figure 29, at level of the styles and 
 
 stamens. X 5. 
 Fig. 32. Transverse section of the bud shown in figure 29, at level of the ovarian 
 
 cavity, showing first rudiments of ovules. X 5. 
 
THE FRUIT OF OPUNTIA FULGIDA. 59 
 
 Fig. 33. Transverse section of the sterile base of the same flower bud as that shown 
 
 in figure 29, showing the ring of vascular bundles, with fascicular 
 
 cambium already established. X 5. 
 Fig. 34. Transverse section of an older flower bud through seven styles or stigmas, 
 
 the stamens, petals, and sepals. X 5. 
 Fig. 35. Part of an approximately transverse section of the flower shown in figure 34, 
 
 giving details of structure of style and stigma, including the papillose 
 
 lining of the stylar canal. X 20. 
 
 Plate 5. 
 
 Fig. 36. Part of transverse section of a stigma, showing papillose surface, and the 
 conducting tissue, vascular bundle, slime-cells, etc., within. X 75. 
 
 Fig. 37. Transverse section through the flower shown in figure 34, showing style, 
 stamens, and wall of ovary with its tubercles, areoles, etc. X 3. 
 
 Fig. 38. Part of transverse section of young ovary, showing long-stalked ovules with 
 integuments initiated, and archesporial cell differentiated. X 24. 
 
 Fig. 39. Transverse section of a young ovary, showing seven placentas with numerous 
 anatropous ovules, also the vascular structure and radial arrangement 
 of photosynthetic cells in tubercle. X 4. 
 
 Fig. 40. Transverse section of slightly older ovary, showing the filling up of the 
 ovarian cavity by the growth of the young ovules and their stalks. Note 
 that the magnification is but half that of figure 39. X 2. 
 
 Fig. 41. Transverse section of mature ovary showing two nearly ripe seeds and a 
 larger number of sterile seeds that have ceased growing at various 
 stages of development. X 2. 
 
 Fig. 42. Transverse section of a persistent, fertile fruit several years old, showing 
 seeds and their stalks completely filling ovarian cavity, the great radial 
 growth of the vascular bundles, and the loss of prominence of the 
 tubercles. X 2. 
 
 Fig. 43. Transverse section of the sterile base of a fruit like that of figure 42, show- 
 ing the large central mass of water-filled parenchyma, the radial growth 
 of the vascular bundles from the activity of the fascicular cambium, and 
 the generally smooth, rounded outline of the surface. X 2. 
 
 Fig. 44. Transverse sections of vascular bundles from ovaries of various ages, all at 
 same magnification, to show relative growth of the phloem and xylem 
 regions of the bundle, (a) From ovary of a flower from which the 
 perianth has just fallen; (ft) from one-year fruit; (c) from a fruit 6 or 
 8 years old, 35 millimeters in diameter. X 11. 
 
 Fig. 45. Transverse section of lower third of nearly mature leaf from the ovary of a 
 flower about ready to open, showing flattened form, vascular system, 
 slime-cells, and the slightly specialized palisade. X 42. 
 
 Fig. 46. Transverse sections near tip of leaf from flower bud, showing small vascular 
 strand, slightly developed palisade, and large air-canals. X 50. 
 
 Fig. 47. Surface view of a flower bud some time before opening, showing sepals and 
 petals and six areoles. Two of the latter have already initiated flower 
 buds, in which the spindle-shaped leaves of lower part of ovary and the 
 flattened sepals and petals can be distinguished. Each of the remaining 
 areoles shows a leaf-scar and the dense tuft of trichomes, with its inner 
 border of spicules and its one or several embedded nectaries. X 3. 
 
 Plate 6. 
 
 Fig. 48. Part of transverse section near top of opening flower, showing upper surface 
 of an areole and a cross-section of the subtending leaf. Among the 
 trichomes of the areole are ten nectaries, and about its inner border is a 
 group of a dozen or more bristles or glochidia. X 2. 
 
 Fig. 49. Part of a transverse section of a recently opened primary flower, showing 
 edge of cup of flower and three tubercles, one of them bearing an areole 
 with two nectaries and the bud of a secondary flower. The arrow indi- 
 cates the sagittal plane. X 3. 
 
60 THE FRUIT OF OPUNTIA FULGIDA. 
 
 Fig. 50. Radial or sagittal section of an areole of a primary flower, showing the 
 growing-point or stem apex of the areole, its bordering groups of bristles 
 and trichomes, two nectaries, and the subtending leaf. X 18. 
 
 Fig. 51. Three typical trichomes from an areole, showing their swollen tops and 
 slender bases. X 45. 
 
 Fig. 52. A single trichome from an areole, showing thick-walled pitted cells of tip. 
 X 110. 
 
 Fig. 53. A mature spine, showing the swelling at base, the barbed tip, and the trans- 
 parent sheath attached for its lower sixth, while the upper five-sixths of 
 it is loose and has slipped down by splitting and folding near the base 
 to leave the tip of the spine exposed. X 5. 
 
 Fig. 54. The upper fourth of an immature spine, showing in detail the intact striated 
 sheath and the barbed tip of the spine itself. X 50. 
 
 Fig. 55. Transverse section of a spine from a young fruit, showing the sheath of 
 loosely packed hairs and the spine with its core of closely compacted 
 small cells and its outer layers of large thick-walled barb-cells. X 110. 
 
 Fig. 56. Part of a sagittal section of an areole, showing a nectary with bristles and 
 trichomes at its base, with the separated, cutinized layer of the epi- 
 dermal cells at its tip; also the vascular supply of the nectary and of 
 the subtending leaf. The leaf is just being cut off to leave a relatively 
 small leaf-scar. X 45. 
 
 Fig. 57. Surface view of upper half of a mature spicule or glochidium, showing the 
 barbs closely resembling those of spines. X 72. 
 
 Fig. 58. Longitudinal section of basal fourth of a nearly mature bristle, showing 
 internal structure, barbs, and zone of rupture at which bristle breaks 
 off. X 125. 
 
 Fig. 59. Transverse section near middle of an immature spicule, showing the large, 
 thickened surface cells which are to give rise to the barbs. X 225. 
 
 Fig. 60. Longitudinal section of upper half of opening flower, showing the most fre- 
 quent location of the abscission layer, which cuts off the whole perianth 
 from ovary, but leaves style to be cut off independently. X 3. 
 
 Fig. 61. Section similar to that in figure 60, showing another type of abscission layer, 
 which cuts off the style as well as the perianth. Separation has already 
 occurred in the left half, while the abscission cells on the right are in 
 the stage shown in figure 67. X 3. 
 
 Fig. 62. Part of longitudinal section of wall of an ovary from which the perianth has 
 fallen, showing surface left after the break through the youngest cells 
 of the abscission layer. The arrow is parallel to the basal part of the 
 style. (Cf. figure 67.) X 48. 
 
 Fig. 63. Part of radial section of perianth-scar of very young fruit, showing phellogen 
 layer and cork. Abscission surface at right. X 117. 
 
 Fig. 64. Part of radial section of perianth scar of a two-year old fruit, showing the 
 parenchyma of fruit at left, phellogen in the middle, and cork at right. 
 X 110. 
 
 Fig. 65. Small portion of section similar to that in figure 64, showing structure of two 
 of the thickened cells in the cork. X 225. 
 
 Fig. 66. Outline of vascular system of inner petal. X 5. 
 
 Plate 7. 
 
 Fig. 67. Part of the radial section of ovary of newly opened flower illustrated in 
 figure 59, showing various stages in the division of cells that are forming 
 the abscission layer. The arrow is parallel to the style. X 110. 
 
 Fig. 68. Part of radial section through ovary of an opening flower, showing the rela- 
 tion of the abscission layer to the vascular bundles and to the mucilage 
 cells. X 19. 
 
 Fig. 69. Part of transverse section of two-year vegetative joint, taken through a 
 tubercle just below its areole, showing the structure of the epidermal 
 and of the palisade-like chlorophyll-containing tissues of the stem. 
 X45. 
 
THE FRUIT OF OPUNTTA FULGIDA. 61 
 
 Fig. 70. Transverse section of a two-year vegetative joint, at about 2 centimeters 
 above base, showing vascular bundles and the radiate arrangement of 
 the palisade tissues in each tubercle. (Cf. figures 39 and 43.) X 1.5. 
 
 Fig. 71. Part of transverse section of tubercle of an unopened flower, showing epi- 
 dermis, stomata and palisade with its intercellular air spaces. X 205. 
 
 Fig. 72. Small portion of transverse section of two or three year old fruit, showing 
 details of stomata of the epidermis and its thick-walled underlying 
 layers. X 365. 
 
 Fig. 73. Small portion of transverse section of tubercle of similar fruit, showing 
 resemblance of the palisade, etc., to that of the vegetative joint. (Cf. 
 figure 69.) X 110. 
 
 Fig. 74. Part of tangential section of tubercle of a two-year vegetative joint, showing 
 palisade cells and mucilage cells in cross-section. X 85. 
 
 Fig. 75. Section of one of the crystal-holding cells so abundant in the subepidermal 
 and parenchymatous tissues. X 365. 
 
 Plate 8. Photographs 76 to 79, 0. fulgida; 80, Caixistemon; 81, O. ^-ersicolob. 
 
 Fig. 76. Lateral view of a five months' seedling, showing hypocotyl, cotyledons, and 
 
 first joint of stem. Seed planted April 27, 1917; photograph of living 
 
 seedling made October 12 following. X 0.9. 
 Fig. 77. Part of a cluster of fruits collected at Tucson in April 1915, showing one 
 
 chain of 14 links in a single linear series. X 0.3. 
 Fig. 78. Plantlet 10 months old, developed in a greenhouse in Baltimore from a fallen 
 
 fruit, showing position of adventitious roots and structure of the new 
 
 shoots. X 0.66. 
 Fig. 79. One of the two examples found in which the persistent fruits of 0. fulgida, 
 
 while still attached, proliferate to vegetative branches. Collected and 
 
 photographed at Tucson in April 1915. X 0.45. 
 Fig. 80. Branch of Callistemon speciosum, with three generations of flowers and 
 
 fruits, showing the persistence and growth of the firm green capsules. 
 
 Flowers at the tip about to open. Collected on the campus of the Uni- 
 versity of California in March 1916. X 0.23. 
 Fig. 81. Gall fruit of 0. versicolor. Collected and photographed at Tucson in April 
 
 1915, showing the curling of the abortive petals and the fly Asphondylia, 
 
 which has just escaped from one of the pupa cases projecting from the 
 
 side of the gall below the fly. X 0.3. 
 
 Plate 9. Photographs of 0. versicolor. 
 
 Fig. 82. A branch of 0. versicolor bearing several clusters of fruits and galls of 1914, 
 and groups of flower buds of 1915. Some of fruit-like structures are 
 clearly galls, but others are nearly, if not quite, normal. Collected and 
 photographed at Tucson, May 1915. X 0.45. 
 
 Fig. 83. A piece of a vegetative joint of 0. versicolor collected at Tucson in April 
 1915, showing 3 types of persistent fruits or galls. X 0.6. 
 
 Fig. 84. Four types of gall fruits of 0. versicolor, showing, at left, a slightly devel- 
 oped perianth; and, at right, a very liighly developed perianth. Col- 
 lected and photographed at Tucson in April 1915. X 0.45. 
 
 Fig. 85. Branch of 0. versicolor with two galls of 1913 or 1914. One of these bearing 
 two vegetative branches developed in 1914, and each of these a cluster of 
 flower buds for 1915. Collected and photographed at Tucson in May 
 1915. X 0.45. 
 
 Fig. 86. Branch of O. versicolor, showing persistent fruit (normal?) bearing a vege- 
 tative branch which is directed backward toward base of the parent 
 branch. Tucson, April 1915. X 0.45. 
 
62 THE FRUIT OF OPUNTIA FULGIDA. 
 
 Plate 10. Photographs of O. discata, 0. cylixdrica, O. leptocaclis, and 
 o. catacantha. 
 
 Fig. 87. Portion of joint of O. discata bearing a gall fruit with projecting pupa cases 
 
 from which the cactus flies have just escaped. X 0.45. 
 Fig. 88. Tip of a joint-fruit of 0. cylindrica of 1913, bearing a persistent fruit of 1914, 
 
 two flowers and a vegetative joint of 1915. Note constriction only, 
 
 instead of the usual distinct articulation at base of the parent fruits. 
 
 X 0.45. 
 Fig. 89, a, b, c. Three branches of 0. leptocaulis bearing fertile fruits of 1914, sterile 
 
 fruits, various forms of more or less fruit-like branches, and also (c) 
 
 flower buds for 1915. X 0.45. 
 Fig. 90. A single joint of O. catacantha bearing four chains of fruits (all sterile), 
 
 showing one chain of six links on right and a single open flower on left. 
 
 Collected at St. Thomas, Virgin Islands, May 1915. X 0.45. 
 Fig. 91. Series of fruits of 0. catacantha (from same collection as those in figure 90) 
 
 in surface view, also in longitudinal and transverse section, showing 
 
 perianth-scar and small sterile ovarian cavity. X 0.45. 
 
 Plate 11. Photographs of Peireskia, Opuntia rxjfida, 0. arbuscula, and 
 O. leptocaulis. 
 
 Fig. 92. Two generations of flowers of Peireskia guamacho, showing proliferation 
 of primary flower from axillary buds at the level of the ovarian cavity 
 (indicated by an x). The primary flower and the secondary one at 
 right are shown in median longitudinal section. X 0.6. 
 
 Fig. 93. Flower and fruit of Peireskia guamacho, showing umbilicate fleshy fruit 
 with areole on right side above. X 0.9. 
 
 Fig. 94. A joint of 0. rufida bearing three persistent fruits, from one of which a new 
 vegetative joint has arisen. X 0.45. 
 
 Fig. 95. Two lower branches of 0. arbuscula bearing persistent fruits, and these, as 
 well as the normal vegetative joints, bearing slender condensed shoots 
 with closely packed areoles. X 0.45. 
 
 Fig. 96. Branch of 0. leptocaulis showing fruits and fruit-like branches, like those 
 described for figure 89. X 0.45. 
 
 Plate 12. Drawings of O. fulgida. 
 
 Fig. 97. Tangential section of half-grown seed, perpendicular to the flattened sides of 
 seed and passing through micropyle, showing pocket of funiculus which 
 incloses the seed and the two integuments. X 95. 
 
 Fig. 98. Section of ripe seed in plant of greatest diameter, showing embryo, endo- 
 sperm, integuments, and thick wall of funicular pouch with its included 
 vascular bundle. X 17. 
 
 Fig. 99. Longitudinal section of a fruit which has given rise to a new plantlet, show- 
 ing the portion of the fruit cut off by a layer of cork from participation 
 in the new plant. X 1.33. 
 
 Fig. 100. Longitudinal section of a fallen fruit through the point of origin of an 
 adventitious root from the border of an areole. X 14. 
 

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