A. B. CONNER, DIRECTOR

College Station. Texas
BULLETIN NO. 612

\V. S. FLOR-YfJRq and F. R. BRISON

Division of Horticulture

 

AGRICULTURAL AND MECHANICAL COLLEGE OF TEXAS
T. O. WALTON, President

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Agflcultural gbgéiefirfiiiiififii 

PROPAGATION OF A RAPID GROWING
SEMI-EVERGREEN HYBRID OAK

TEXAS AGRICULTURAL EXPERIMENT STATION
i

MAY 1942

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Figure 1. Frontispiece. First generation Ness Hybrid oaks. Approximately
30 years old. These resulted from pollinating the live oak with pol-
len of the overcup oak. Note the rounded, symmetrical, yet upright
form, and the dense foliage. a

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A beautiful oak has resulted from a cross of the live oak and overcup
oak made over 30 years ago by Helge Ness at the Texas Agricultural
Experiment Station. It is a partially evergreen, round-topped tree that
grows faster than either parent and should be well adapted for orna-
mental planting in east, central, and probably other parts of Texas.

Several successful methods are presented for the propagation of this
desirable oak. It is shown especially that when scions are either whip
or bark grafted on burr, live, overcup, post, swamp white and other
stocks of the “white 0a ” group, a high percentage of good unions are
secured.

Results have shown also that certain methods are unsatisfactory, and
that one group of stocks have made poor unions; both should probably
be avoided in nursery practice.

CONTENTS

Page
Introduction 5
The material 5
Study of methods of propagation
Attempts to root cuttings
Discussion of rooting of cuttings 9
Attempts; to propagate by T-buds 12
Propagation by grafting 13
Stocks 13
Graftwood 14
Grafting methods used 14
Presentation and discussion of grafting data _ 15
Comparison of methods 15
Comparison of stocks 18
1940 grafts 18
1941 grafts 19
1940 and 1941 grafts considered together 22
Microscopic examination of graft unions 24
Heights of grafted and ungrafted seedling stocks compared ______ __ 28
General discussion of grafting ‘ 29
Factors favoring success of stocks 30
Summary 31

Literature cited. 3 2

PROPAGATION OF A RAPID GROWING SEMI-EVERGREEN
HYBRID OAK

By
\V. S. Flory, Jr.,‘ and F. R. Brison?

In 1909 Helge Nessg, at that time Horticulturist With the Texas Ex-
periment Station, pollinated some pistillate flowers" of a live oak with
pollen from an overcup oak. Three hybrids resulted. Similar crossses
in 1910 gave 3 more hybrids. Additional crosses in later years gave
still others. In securing these crosses‘ Ness was pioneering in a virgin
field. So. far as available published reports show, he was the first man
in America and among the first in the world to produce artificial hybrids
between species of forest trees.

The Texas Experiment Station has‘ attempted to stimulate an initial
interest in these desirable trees for ornamental purposes, and to develop
suitable methods for their propagation. While the Station cannot propa-
gate the trees for general distribution, and must rely on Texas nurseries
for this function, it will gladly furnish lists of nurseries known to have

Ness Hybrid trees as they become available. No attempt has as yet

been made by this station to develop practical means of producing
hybrids of hardwood trees on a scale necessary for commercial timber
production.

THE MATERIAL-

These hybrid oaks‘ were first described by Ness in 1918 (10). In
1927 he published (11) further descriptive notes on the first generation
hybrids and also briefly described the different classes of segregates in
a second generation population. Segregation of characters in F2, from
a factorial standpoint, was later studied by Yarnell (17). Both Ness
and Yarnell have pointed out that the first generation hybrids have a
considerably more rapid growth rate than either of the parent species.
This exhibition of hybrid vigor is striking when the original hybrids
are compared in size with live and overcup oaks planted within a few
years of the same time.

The first generation live oak >< overcup oak hybrids are uniform.
Their upright and straight-branched habit, inherited from the overcup
parent is combined with a round top and in addition a greater regularity
of outside contour than is usual for live oaks. The resulting upright-
symmetrical form, so regular in outline as to appear sheared (Fig. 1),
gives the hybrids a distinctive beauty. The lyrate leaves are inter-

lHorticulturist, Agricultural Experiment. Station.

2Proiessor of Horticulture, School of Agriculture. A. and M. College of Texas.

“Deceased December 30, 1928. _

was also produced some hybrids, o-f less ornamental promise, between other oak species (see
reference 11). Where the terms “Ness Hybrids" or merely “hybrids” are used in this paper,
however, they refer to plants resulting from the live oak x overcup oak cross.

6 * BULLETIN NO‘. 612, TEXAS AGRICULTURAL EXPERIMENT STATION

Figure 2. Leaves and fruit of the Ness Hybrid oak and its parents. A.—the
live oak parent (Quercus virginiaaza); B.—the overcup oak parent
(Q. lyrata); and C.—the 1'1 live oak x overcup hybrid.

PROPAGATION OF A RAPID GROWING SEMI-EVERGREEN HYBRID OAK 7

mediate in shape and size between those of the parents (Fig. 2). The
trees hold half of their leaves through an average winter at College
Station. In very mild winters they retain practically all of their leaves,
but in unusually cold seasons the majority of these are dropped. This
same tendency is approached in a lesser degree by live oaks.

The regular form, round top, good size, approach to evergreenness,
and comparatively rapid growth rate, are all very desirable characteristics

. for hardwood trees. Combined as they are in the Ness Hybrids, it makes

them valuable ornamental plants. They should add materially to land-
scape planting over the state if they could be successfully propagated
and distributed.

A second generation population of 23 individuals started by Ness in
1923 is still growing at College Station. Threelarger second genera-
tion (or F2) populations, totalling about 326 plants, have been grown
during the past 6 years by the senior writer of this article. Broad
leaved, heavy foliaged, evergreen segregates are occasionally encountered
in the second generation. Eleven plants, among the 326 recently grown,
appeared especially promising and have been saved. Some of these are
rapid growing and may prove to be even more desirable than the first
generation Ness Hybrids. Some preliminary work indicates that meth-
ods, to be described later, for grafting of the F1 Ness Hybrids would be
equally applicable to desirable F2 live oak >< overcup oak hybrids.

STUDY OF METHODS OF PROPAGATION

During the past several years attempts to propagate the F1 Ness
Hybrids have been made and have now met with at least a measure of
success. The methods of propagation used and the results secured are
described in this paper. The first trials were with cuttings (4, 6).
It would seem that if this hybrid material could be disseminated on its
own roots that this would probably be the most satisfactory procedure.
Attempts to propagate the hybrids on roots of other species by T-budding
(4) have also been carried out. As the two sections in this paper deal-
ing with cuttings and with T-budding will show, practically no success
has followed the use of either of these methods. Propagation by graft-
ing (5), however, has met with considerable initial success. Only time
can tell how permanent the graft unions-—and hence ultimate success
of the propagation—will be. These grafts, made up of the first gen-
eration hybrid oak scions and of several different stocks, look promis-
ing enough at the present time that they are being sent out to interested
nurseries. Trees grafted in 1940 have already been distributed and
those grafted in 1941 will be available for future distribution; scion
wood from the hybrid trees will be supplied where desired. It is thought
that this material can thus serve as a source for further propagation
and distribution by the several nurseries. By 1944 some trees should
be available from nursery sources, and the supply should meet the ordi-
nary demand-s in subsequent years.

8 BULLETIN NO. 612, TEXAS AGRICULTURAL EXPERIMENT STATION

Attempts t0 Root Cuttings

Numerous attempts have been made to propagate the hybrid oaks by
rooting either stem or root cuttings. Various treatments have been given
s-everal thousand cuttings in such attempts. Cuttings were made at dif-
ferent times of the year, both from current season and also from one-
and two-year old wood. The treatments and results are summarized in
Table 1. Results have been consistently negative; no living plants have
been secured so far from cuttings.

Different lots of cuttings were treated with the following growth pro-
moting substance, or hormones: indolyl acetic acid, indole-3-N-propionic
acid, 'y-(indole-3)-N-butyric acid, naphthalene-acetic acid, and the com-
mercial Hormodin A which contains v-(indole-3)-N-butyric acid and Kak
solutions‘.

The different chemicals were used in various concentrations and for
treatment intervals varying usually from 24 to 72 hours depending to
some extent upon the concentrations. It also may be noted from Table 1
that cuttings in some cases were treated with vitamin B1 (1 part vita-
min: 1 million parts water) both immediately following Hormodin A
treatment, and at intervals" following such treatment. This is essentially
the method that was successfully used by Went et al (16) in the rooting
of etiolated pea cuttings and leafy cuttings of lemon and of Camellia.

Treatments were given stem cuttings by soaking from one-half inch
to one inch of the base in the hormone solutions. Root cuttings were
either entirely immerse-d in aqueous solutions, or were bored and in-
serted with tooth picks which had been soaked with and contained the

growth substances (approximately 2 mg. per pick) in crystalline form.‘

This tooth-pick method was devised by Romberg and Smith (14) who
have had success in stimulating the formation of new roots on trans-
planted pecans by its‘ use. ’ l

Most cuttings were placed either in sharp white sand, or in a mixture
of equal parts of this sand and peat moss; the lots were about equally
divided between the two media. The large lots 1 to 6 and 1A and 2A
(Table 1) were divided between four media. These included the two
just mentioned and in addition red river-sand, and also a mixture of
equal parts of red river-sand and peat moss.

Following a suggestion of Dr. C. L. Smith, of the U. S. D. A. Pecan
Laboratory, Brownwood, Texas, callusing of cuttings prior to chemical

treatment was attempted. This was done with the following lots listed ,

in Table 1: 20A to 31, 33, 38 to 40, 57 to 60, and 136 to 144. It was
found with oak material, as had Dr. Smith with pecan wood, that cuttings
from dormant wood when placed in moist not wet-—sphagnum moss
in a constant temperature oven at about 85°C. practically all callused
heavily in from 1 to 3 weeks. Greenwood cuttings seldom callused by
this method. A few of the callused cuttings both from untreated and
from chemically treated lots produced weak root growth but the rooted
cuttings all died.

PROPAGATION OF A RAPID GROWING SEMI-EVERGREEN HYBRID OAK 9

A series of treatments using different growth substances in several
powder or dust bases have been run with cuttings from live oak trees.
The results, as with material treated in aqueous solutions, were all
negative. On the basis of other experience with cuttings from live and
from hybrid oaks we would anticipate similar negative r-esults from the
treatment of material from the hybrid forms with growth substances
in powdered bases.

Discussion on Rooting of Cuttings

Available reports concerning attempted propagation of oaks by cuttings
are not numerous. Hutchings and Larsen (8) failed to root cuttings
of white oak following various chemical treatments‘. Bailey (2) men-
tions that evergreen species are occasionally incr-eased by cuttings, but
no details are given.

Thimann and Delisle (15) have arrived at some interesting results,
concerning the rooting of cuttings from “diflicult” plants, which may
have an important bearing on the present work. They have pointed out
that there are 3 groups of trees which are diflicult to propagate by cut-
tings. These are: “(1) a majority of the conifers, (2) many forest
hardwoods and (3) the apples and related rosaceous trees.” A number
of factors which might afiect the rooting of cuttings were considered in
their work. Among these were:

(1) The age of the tree from which cuttings were taken.
(2) Optimum auxin treatment.

(3) Relative rooting behavior of different parts of the plant.
(4) Rooting medium and temperature.

(5) Factors other than auxin such as sugar and vitamin B1.

They found that “The most important single factor in rooting these
‘diflicult’ trees‘ is the age of the tree from which cuttings are taken.
The ease with which roots are formed (on cuttings of one-year wood)
falls off steadily with increasing age of the tree. This applies both in
the presence and in the absence of auxin (hormone) treatment.” In
general it was found that cuttings from one-year old trees rooted well
without auxin treatments; cuttings from 3 and 4 year old trees gave
good rooting with optimum auxin treatments; but with a number of
species cuttings from old trees could not be induced to root. This was
true, among others, of cuttings from the Red Oak, Quercus borealis.

The work just cited confirms the work of Gardner (7) with respect to
rooting cuttings of 1-year old plants. Further, it puts this observation,
apparently, on a practical basis by advancing the rooting age of tree ma-
terial up to 3 or 4 years—an age size from which several cuttings may be
secured per plant-—provided the proper auxin treatment is given.

McGinnis (9) has propagated live oaks by terminal cuttings from dor-
mant wood of nursery, and hence fairly young trees.

Now the cuttings from the hybrid oaks used in the present instance were
secured from the trees resulting from Ness’ 1909 and 1910 crosses. Thus

 

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12 BULLETIN NO. 612, TEXAS AGRICULTURAL EXPERIMENT STATION

they were from trees between 25 and 30 years of age. The obvious impli-
cation, from the work of the investigators mentioned above, is that the
age of these tree-s is a limiting factor virtually preventing rooting of cut-
tings from them when treated by known methods. To overcome this handi-
cap the live X overcup oak cross, first made by Ness, has been repeated.
Several young seedlings are now available as sources for cuttings-which
may possibly be induced to root by proper treatments.

Attempts to Propagate by T-Buds

Over a period of four years several hundred buds from the first genera-
tion hybrid oaks have been T-budded into young stock of several oak species
and hybrids. In 1938 buds were inserted in August. ln 1939 and 1941
budding was done during May. In 1940 the buds were inserted during
October, with the thought that these might unite before growth ceased in
the fall, and after remaining dormant over winter could be forced into

Table 2. Number of hybrid oak T-‘buds inserted in several stocks at diflerent
times of the year, with negative results.

 

Oak stocksl Time of bud insertion i
(acorns from open pollinations) Total
August May October May
1938 1939 I 1940 1941

Bung ____________________________________________________ _._ 15 23 ________ -_ 38
Chinese ________________________________________ -- 15 15 17 10 * 57
Live ____________________________________________ __ 10 15 ________ -- 25 50
Overcup ________________________________________ - - 5 10 102 -------- - -3 25
Pin _____________________________________________ _._ 5 5 , 6 ________ __ 16
Post- ____________________________________________________ -- 10 9 -------- -- 19
Spanish __________________________________________________ _._ 5 2 ________ __\ 7
Water __________________________________________ __ 10 10 8 ........ __ 28
Willow _____________________________________________________________ __ 4 ________ _- 4
F2 (Live >< Overcup) _________________________ __ 10 15 l 20* ________ -- 45
Fa (Live x Overcup) _____________________________________________ n, 11 -------- -- 11
F2 (Live >< Swamp White) ___________________ __ 20 15* i 26 15 76

TotaL _____________________________________ _- 75 115 i 13o 50 s76

lSee next section, “Propagation by Grafting,” for scientific names of the various stocks.
ZOne bud from this lot produced a tree.

growth in the spiring. A summary of the number of buds inserted, at
different times and on several stocks, is given in Table 2. Results have
been almost entirely negative. One bud inserted on an overcup oak whip
in October 1940 united and has grown into a young tree. This was the
only bud, out of 376 ‘set, to unite and grow.

The reason for the failure of the T-buds is not known. The bark of the
stock slipped well when the budding was done. The buds were inserted
with only a very thin sliver of wood included. The technique used in the
budding appeared, and was considered, satisfactory. When the rubber
bands used for tying were removed at the end of 10 days a large per cent
of the buds were green in color and aipipeared to be alive. Usually inspec-
tion after 4 or 5 weeks revealed the same condition. But after that the

 

Ttas‘ § n? viz-Z-
Zoztfigl?’

PROPAGATION OF A RAPID GROWING SEMI-EVERGREEN HYBRID OAK 13

stock bark started curling back, allowing the bud to drop out. Inspection
of a number of buds was made after 4 weeks; if any callusing had occurred
it was difiicult to identify by macroscopic examination. The buds ap-
parently remained green in color for same time but without anatomical union
taking place.

Propagation by Grafting

The desirability of attempting graftage was emphasized when the nega-
tive results with cuttings and with the first bud insertions" became ap-
parent.

Stocks

Stocks for possible grafting or budding were already being grown from
acorns secured in the fall of 1936, 1937, and 1938. The acorns were strati-
fied from time of gathering until planted in the nursery about the first of
January following collection.

The oaks used as stocks, with their relationship in the genus Quercus
according to Rehder (13) are as follows:

Subgenus II. Erythrobalanus—Black oaks (acorns mature the 2nd year).

Quercus nigra L. (Water O.)

Q. marilandica Muenchh. (Black Jack)

Q. rubra L. (Spanish O.)

Q. palustris Muenchh. (Pin. O.)

Subgenus III: Lepidobalanus—White oaks (acorns mature the first or
second year).
Section 1. Cerris (Fruit biennial.)
Q. serrata Sieb. & Zucc. not Thumb. (Chinese O.) (fruit
usually ripens the first Year in Texas)
Section 3. Ilex. (Fruit usually annual)
Q. virginiana Mill. (Live O.)
Section 6. Prinus (Fruit annual)

Q. albd L. (White O.)

Q. stellata Wangh. (Post O.)

Q. Zyratm Walt. (Overcup O.)

Q. macrocarpa Michx. (Burr O.)

Q. bicolor Willd. (Swamp White O.)

The first four of these fall in the group commonly designated black or
pin oaks, the last six belong to the class often collectively called white oaks.
Bailey (2) uses the terms black oaks and white oaks to designate the col-
lective species in the subgenera Erythrobalanus and Lepidobalanus, respec-
tively. The Chinese oak, representing the extreme of the subgenus L-epido-
balanus nearest the black oaks resembles the latter group in several mor-
phological characters and in grafting behavior with the Ness Hybrid scions.
In the discussions of this paper it is considered, for convenience, along with
the black oaks. Most of the species used are Texas natives. Quercus palus-
tris and Q. bicolor approach, but do not often occur within the borders of the

14 BULLETIN NO. 612, TEXAS AGRICULTURAL EXPERIMENT STATION

state. The Chinese oak, as its name suggests, has» been brought to this
country from the Orient. In addition to the pure species, seedling stocks
derived from two of Ness’ hybrids have been used. These latter are second
generation (or “F2”) open-pollinated seedlings of the crosses live oak ><
overcup oak, and live oak >< swamp white oak.

Acorns of the native forms are usually available. If desired for stock
seed they should be gathered as soon after ripening as possible and then
within a few days, should» be stratified in moist sand, or planted in nursery
rows where they will remain moist. Acorns properly treated usually pro-
duce excellent seedling stands, but seed of many oaks germinate very poorly
if allowed to air dry for even a few weeks.

Graftwood

With the methods of grafting followed in this experiment it is customary
to use one-year-old scions. Normally these should be about three-eights of
an inch in diameter. Preferably they should be straight and unbranched.
The Ness Hybrids do not produce such scions abundantly. Their growth
habits, in mature trees especially, often result in branching before the limbs
attain suitable size. Some of the available scions were straight, unbranched
shoots of 1-year-old wood; others were of 2-year-old Wood. When the latter
type was used, care was taken to leave a 1-year-old side branch on each
scion if possible. Some scions consisted of a 2-year-old base and a 1-year-
old terminal portion. At the point of mergen-ce of the 1- and 2-year-old
woods there were formed numerous buds which developed and grew satis-
factorily under favorable conditions. '

The scions were cut each year during February, while the trees were still
dormant. They were then packed in moist sphagnum moss and kept in
cold storage until used for grafting. The temperature of the storage vault
ranged from 34° F. to 40° F.

Grafting Methods Used

Whip Graft.——This method was used mainly on rootstocks which were
from % to ‘$4 inch in diameter. Soil was removed from around the
bases of the seedling stocks and the grafts were inserted slightly below
the ground level. They were tied with cotton twine; no waxing ma-
terial was used. Finally, moist soil was pressed closely about the graft
leaving only the tip exposed.

Bark Graft and Inlay Graft.—-These two methods are quite similar.
Results of the few inlay grafts made are tabulated with those of bark
grafts. Usually stocks that were about 1-inch in diameter were used for
these grafts. Generally they were set within one foot of the ground.
They were tied with cotton twine and either grafting wax or melted
paraflin was applied in order to exclude air from all open surfaces and
prevent drying. _

Some of the stock species could not be grafted readily by either of
these two methods, because of the difiiculty encountered in getting the
bark to separate from the wood. This was particularly true of water
oak, 2- and 3-year old burr oak, and Chinese oak stocks.

PROPAGATION OF A RAPID GROWING SEMI-EVERGREEN HYBRID OAK l5

\ Cleft Gra.ft.—This method likewise was used on stocks that were 1-
inch, and often larger, in diameter. Grafts were usually set within 1 foot
of the ground. Cleft grafts were also tightly tied with cotton twine,
and covered with grafting wax or melted paraffin.

Detailed description of the general grafting, as well as budding, meth-
ods used in the present work may be found in numerous books and bul-
letins including those of the United States Department of Agriculture
(3, 12).

As the grafts produced growth and were in danger of mechanical or
wind breakage they were staked with laths and tied up periodically.
Until mid-summer the grafts were inspected about every 10 days for (1)
removal of stock buds and shoots, (2) rewaxing‘ where necessary, and
(3) additional tying when growth warranted. After about July 15 a
check on these points was made every 15 or 20 days during the growing
season. The strings tying the grafts in place were removed before the
stock diameter increased enough for damage from girdling to occur.
Rainfall was much above average both in 1940 and 1941. In seasons of
lighter rainfall lower growth rates might not necessitate such frequent
checks.

PRESENTATION AND DISCUSSION OF GRAFTING DATA
Comparison of‘ Methods

The percentage of grafts which live and grow appears the most obvious
criterion for determining the initial value of a grafting method or of the
kind of stock used. On this basis, reference to the percentage figures in
the lowest row of Table 6 offer a ready comparison of the grafting suc-
cess resulting from the three methods used. Fifty-nine per cent of all
whip grafts and 68 per cent of all bark grafts, but only 20 per cent of
the cleft grafts made, were successful.

From Table 3 it may be seen that of the grafts made in 1940 the whip
grafts were considerably the most successful on a percentage basis. The
data of Table 4 show that the whip grafts made in 1941 were again
quite successful. But in the latter year even greater success" resulted
from use of the bark graft method; this point is discussed further in
the next paragraph.

A comparison of summary figures in Tables 3 and 4 shows a much
higher percentage of bark grafts to have been successful in 1941 than in
1940. In 1940 all bark grafts were made just after the sap started to
flow but before many buds had burst. At that time difficulty was en-
countered in getting bark to “slip” without stringing. In 1941 the ma-
jority of the bark grafts were made some two weeks after leafing began,
and at that time the bark slipped cleanly on many of the stocks. The
disparity in percentage of unions in the two years‘ can apparently be
traced directly to this difference in ease of working the bark on the dif-
ferent occasions. When making bark grafts with oaks, then, it would seem

16 BULLETIN NO‘. 612, TEXAS AGRICULTURAL EXPERIMENT STATION

wise to delay insertion until well after stock dormancy has broken. The
scions, of course, should be held dormant until used.

The percentage of successful cleft grafts was low in 1940 and still
lower in 1941; As pointed out earlier most wood used for cleft grafts
in the present work has been above an inch in diameter. It was ob-
served that where ideal fits were secured with most stocks that a high
proportion of cleft grafts united. But such fits were diflicult to fashion.
It has seemed obvious that size and hardness of the wood used, result-
ing in many poor fits between stock and scion, have been responsible
for the unfavorable results in many cases. The use of wood of smaller
diameter would probably make for closer fit and increased success with
the cleft type of graft.

Despite results from bark grafting in 1940 it seems apparent that both
whip and bark grafting are methods that will give a high percentage of
successful unions with compatible stocks. Cleft grafting, at least with
larger sized stocks, is a less successful method.

17

PROPAGATION OF A RAPID GROWING SEMI-EVERGREEN HYBRID OAK

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18 BULLETIN NO. 612, TEXAS AGRICULTURAL EXPERIMENT’ STATION

Comparison of Stocks

1940 Grafts

The data for the grafts made in 1940 are summarized in Table 3. Out
of a total of 162 grafts made, 2 were injured mechanically and are not
included here.

Figure 3. Ness Hybrid oak grafts on I‘: (live oak x swamp
white oak) roots. Whip graft made March 18,
1940. Picture taken July 26, 1941.

On a percentage basis the two outstanding stocks used in 1940-
where 10 0r more grafts were made on similar stocks—-were burr oak and
the hybrid F2 (live >< swamp white) oak (Fig. 3). Favorable percent-
ages of successful stock combinations w-ere also secured, from a smaller
number of grafts, between hybrid scions and seedlings of the F2 (live X
overcup), live oak (Fig. 4), and white oak (Q. alba). Only a small per-
centage of the grafts on Chinese and water oaks grew, and none of those
on black jack were successful.

All living grafts were measured for height on August 15, 1941. On that
date 78 trees living from the 17-month old 1940 grafts averaged 45.2 inches
The figures for all cleft, bark and whip grafts were 63.5, 50.0, and 42.6
inches, respectively. Bark and cleft grafts had been made as near the
ground as convenient, but the stock stubs did give these two types of grafts
some height advantage. Not all the height difference between the trees
from the cleft and whi-p grafts can be accounted for in this way, however.
In general the smaller stocks were used for whip grafts, the largest for
cleft grafts, and bark grafts were made on stocks intermediate in size be-

PROPAGATION OF A RAPID GR-OWWING SEMI-EVERGREEN HYBRID OAK 19

tween the other two. It is- possible that the greater food reserves in the
larger stocks account for at least part of the superior size of the scions
they bear.

Figure 4. Ness Hybrid oak» grafts (2 plants to the right) on
live oak roots, compared with a seedling live oak
(to the left). The hybrid scions were cleft grafted
on March 18, 1940. '.l.‘he photograph was made
July 26, 1941. The live oak seedlings, as well as
the seedlings used here for stocks, were all placed
in the nursery about January 1, 1938. The tree to
the right shows a water sprout starting from the
rootstock; these need to be removed frequently
until the grafts get a good growth start.

1941 Grafts

Table 4 summarizes data on the 1941 grafts. It is seen that all of the
kinds of stocks used in 1940 were used for additional grafts in 1941. Also
seedlings of post, overcup, swamp white, and in a few cases of pin and
Spanish oaks- furnished stocks for other 1941 grafts.

It is evident from the table that more than 60 per cent of the hybrid
scions lived on each of the following stocks: post, F2 (live >< swamp white),
swamp white, live (Fig. 6), burr, overcup (Fig. 7), and black jack. Only
3 grafts were made on black jack, not enough for a reliable te-st. About
65 per cent of the grafts made on the F2 (live >< overcup) seedlings grew
(Fig. 5). Grafts on white oak (Q. a-lba) were not as successful as the few
made in 1940. Poor results were again obtained with grafts on Chinese
and water oaks.

20 BULLETIN NO. 612, TEXAS AGRICULTURAL EXPERIMENT‘ STATION

  

Figure 5. A Ness Hybrid oak graft on roots of an open-
pollinated I‘; (live x overcup) oak seedling. Bark
grafted on April 10, 1941. The picture was made
September 1, 1941, at which time this graft was
58 inches in height.

Figure 6. Ness Hybrid oak. graft on live oak roots. Bark
graft made in early April, 1941. Photograph made
September 1, 1941.

PROPAGATION OF A RAPID GROWING SEMI-EVERGREEN HYBRID OAK

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22 BULLETIN NO. 612-, TEXAS AGRICULTURAL EXPERIMENT STATION

On August 15, 1941, the 138 trees living from the 4-month old 1941 grafts
averaged 36 inches in height. The respective averages for bark, cleft, and
Whip» grafts were 42.2, 38.9, and 22.6 inches.

Figure 7. Ness Hybrid oak grafts on overcup oak stock.
Bark grafts m.ade April 10, 1941. Phffliograph
made July 26, 1941. Note method of tying, and that
much of the twine on the two grafts to the left is
hidden by the waxing material. The plants have
been staked and loosely, but securely, tied to pre-
vent wind damage prior to formation of a firm
graft union. All stock sprouts had been removed
on July 17. Many new sprouts were taken from
the stocks before this picture was made, but the
long one extending upward (to the right) from the
stock of the right hand plant was left to show how
rapidly these sometimes grow during wet periods.
It is easy to see that if many of these were left
on the stock very long that the scion would suffer
as a result.

1940 and 1941 Grafts Considered Together

Table 5 and, more especially, Table 6 present the data of Tables 3 and 4
in combined form. The discussion that Went with the two preceding tables
applies, in general, here, and this, together with the combined data makes
certain conclusions s-eem apparent.

There are 4 stocks on which more than 80 per cent of the grafts made
are alive. These are post, F2 (live X swamp white), burr, and swamp
white. Also 56 per cent or more of the grafts made on stocks of live, over-
cup, and F2 (live >< overcup)" are ‘thriving. Thus there are 7 stocks on
which the hybrids scions may be said to have made a good to excellent
growth. The other stocks used have either resulted in a low percentage
‘of unions or have had too few grafts made on them to indicate their value
correctly. ‘

Table 6 presents a summary, derived from Tables 3 and 4, of the com-
bined grafting results with all white oak stocks, as compared with the re-
sults from all black oaks used as stocks. A consideration of s-ome of the

PROPAGATION OF A RAPID GROWING SEMI-EVERGREEN HYBRID OAK 23

'.I.'a.b1e 6. A comparison of number of grafts made (according to type), and
the number and percentage that were successful, on all white oak
and on all black oak species, respectively.

Kinds of grafts
Grafts on
Whip Bark Whip and Cleft | All
bark i grafts

White oak stocks 5

Number made_ ______________________________ -_ 113 96 209 30 I 239

Number successful ___________________________ __ 9o 79 175 11 l 18c

Per cent successfull _________________________ __ 85 82 84 37 7s
Black oak stocks l

Number made_ ______________________________ __ 71 34 105 61 166

Number successful ___________________________ __ 13 10 23 7 30

Per cent successfull _________________________ -_ 18 29 22 12 , 1g
White + black oak stocks l i

Number made- ______________________________ __ 184 130 314 j 9'1 405

Number successful ___________________________ __ 109 89 198 1s  2.16

Per cent successfull ......................... __ 59 68 I 63 l 20 \ 53

1All percentages expressed to nearest whole number.

data of Table 6 shows some interesting comparisons between results with
white and with black oak stocks. Of the 113 whips grafts on white oak
species 96, or 85 per cent, were successful. Only 18 per cent of the 71
whip grafts on black oaks have grown. With respect to bark grafts 79
of 96, or 82 per cent have been successful on white oaks, but only 10 of 34,
or 29 per cent on black oaks. Thirty-seven. per cent of all cleft grafts on
white oaks, but only 12 per cent of this type on black oaks, grew.

It is of further interest to consider all bark and Whip grafts together.
Two hundred nine of these types of grafts" were made on white oaks, and
175, or 83.7 per cent, of these were successful. Only 22 per cent of the
grafts of these two types made on black oaks grew. -

It appears then that the live >< overcup hybrid grafts readily on th
closely related white oaks used as stocks, but with little success on the
genetically more remote black oaks.

A worthwhile comparison may be made of data in the percentage
columns of Tables 3 and 4. In most cases where as many as 10 grafts
per type were made these percentages of living grafts‘ run rather close
together in the two tabl-es. Where they do deviate considerably it is
usually with the poorer, or black oak, stocks where a larger percentage
of 1941 grafts, than of the 1940 ones, are apt to have been alive in August
1941. "Table 7 gives a comparison of 1940 grafts alive on white oaks
and also on black oaks on s-everal subsequent dates. The arrangement

Table 7. Grafts made in 1940 on white oaks as compared with those on black
oaks, with respective numbers alive on several subsequent dates.

f No. of grafts Grafts alive Grafts alive Grafts alive
Type of ' made March u 4-19-40 4-11-41 8-15-41
Stock 1 18 and 20, 4‘ .,
1940 { Number j Per centl‘ Number l Per centl Number Per ccntl
. 1 i N
White oak ____  ____  so 72 j so as s6 e7 s4
Black oak __________ __ 8O ‘ 61 3 76* 20 25 11 14
Total _____________ -_ 16o 3 13s i as l s9 l 56 a 7s 49

lPeiccntz-igcs are stated in nearest whole numbers.

24 BULLETIN NO. 612, TEXAS AGRICULTURAL EXPERIMENT STATION

of the data in Table 7 brings out clearly that the percentages in Tables
3 and 4 for total number of grafts alive by certain dates, have been
materially lowered by including consideration of the black oak group.
There is a consistent significant decrease in number of viable grafts on
black oak stocks. It is evident that on black oaks‘ there is not only a
lower percentage of initial successes, but those grafts which do start
off are subject to a higher death rate during the first and second seasons
than is the case for the more compatible stocks‘. The decrease in num-
ber of good grafts on white oaks, however, is scarcely more than might
be expected from mechanical injuries.

Microscopic Examination of Graft Unions

Results show that the Ness Hybrids can be grafted readily and suc- 4 ‘

cessfully on certain stocks‘, but not so easily upon others. At the end
of one season’s growth (in 1941) microscopic examination was made
of bark graft unions of the hybrids with live oak, Chinese oak, seedlings
from open-pollinated acorns of the live X swamp white oak cross, post
oak, and overcup oak; also of whip graft unions with burr, and Chinese
oaks.

The sections were cut from fresh material, approximately 30 microns
thick, stained with safranin and gentian violet, and mounted in balsam.

Only a limited number of graft unions were sectioned. Two bark
graft and one whip graft union of the Ness Hybrids on Chinese stock, and
only one graft union on each of the other stocks listed above were sec-
tioned. The grafts on the Chinese oak stocks, selected for microscopic
study, were the most vigorous and promising available; they were
slightly over 3 feet in height. Individuals as representative as" possible
of the other available stocks were chosen. Hence, while these limited
observations cannot be regarded as necessarily representative, it is be-
lieved they do give a rather reliable indication of the union occurring
between the hybrids and the two general types of stocks" (i.e., black and
white oaks).

Sections of the union of the hybrid with live oak and with overcup
oak (Fig. 8) show that the scion and stock each produced callus tissue
from the cambium in considerable quantity. It is apparent from the
position of the poi-nts, X and X1, at which union first took place, that
this process" occurred soon after the graft was made and callus forma-
tion had begun. The lines of union, XY and XlYl, that resulted from
the subsequent growth of the scion and stock were smooth, with no evi-
dence of incompatibility.

Prepared sections through unions of the hybrid on post, burr, and the
F2 (live >< swamp white) oak stocks likewise indicated a free formation
of callus by the two components and a ready union of the new tissues.

Sections of the hybrid on Chinese oak indicated that initial union was
inhibited (Fig. 9). There is evidence here that the stock and scion each
produced the necessary callus. The calluses from the two, however,
apparently did not always unite when they first came in contact. Sec-

PROPAGATION OF A RAPID GROWING SEMI-EVERGREEN HYBRID OAK 25

Figure 8. Cross sections of bark grafts of Ness Hybrid oak on live oak (above)
and on overcup (below). 210.8. Note that union first occurred at
X and K1. The lines X to Y and X1 to Y1 indicate a good strong union
between stock (B) and scion (A).

26 BULLETIN NO. 612, TEXAS AGRICULTURAL EXPERIMENT STATION

tions of one bark graft. (Fig. 9, above) showed that the line of union was
not continuous after union was first established. There is definite evi-
dence of periderm along the surface of the first-formed callus, particu-
larly of that from the stock. This might have been due to poor tech-
nique in inserting the graft, to inadequate waxing and subsequentlex-
posure to air, or to some substance peculiar to the stock species. The
latter is suggested to be the case since it appeared that the periderm
had formed more fully upon the callus from the stock, than upon that
of the adjacent scion. It is noteworthy further that calluses from dif-
ferent parts of the stock formed periderm and did not unite readily
when they came in contact. Sections from the other two grafts studied
(one of which is shown in Fig. 9, below) show a good union with noth-
ing to indicate incompatibility between the stock and scion after union
took place. These observations suggest that the chief difficulty in graft-
ing Chinese oaks may be in obtaining the initial union of callus from
the stock with that from the scion. Any delay in this process, though
it may be slight, results inevitably in loss of vitality of the scion and
decreases its chances‘ of ultimate union. Observations of the sections,
coupled with field behaviour of the grafts, suggests that the prevailing
stock-scion incompatibility with the black oaks is more often due to
physiological reasons than to failure of anatomical union. Additional
data are needed to verify this.

PROPAGATION OF A RAPID GROWING SEMI-EVERGrREEN HYBRID OAK 27

Figure 9. Cross sections through graft of Ness Hybrid oak on Chinese oak-
Above—Bark graft. Arrow indicates periderm-like material which
seems to inhibit initial union of stock (B) and scion (A). Note that
union, K to Y, is not as good as in the sections of Figure 8. Below-
Whip graft. Shows some periderm at X. Note that stock and scion
have made good anatomical union along line X to Y.

28 BULLETIN NO. 612, TEXAS AGRICULTURAL EXPERlMENT STATION

Heights of Grafts and of Ungrafted Seedling Stocks Compared

A number of ungrafted nurs-ery seedlings of several kinds of oaks
were measured for height in mid-August 1941. All of these were put
in the nursery as acorns 0r very young seedlings about January 1, 1939.

Figure 10. Ness Hybrid oak graft on post oak roots. Bark
graft made April 17, 1941. Exposure made Se -
tember 1, 1941, at which time the height of t e
graft was 52 inches, that of the post oak seedling
immediately behind it was 39% inches, and that
of the post oak» seedling in the background was
44 inches. A11 seedlings, whether used for stock
or otherwise, were set in the nursery about Jan-
uary 1, 1939, from acorns gathered in the fall
of 1938.

In Table 8 a comparison can be made between the heights of these seed-
lings and of grafts which have been made on other seedling stocks of

the same kind and set at the same general place and time.
Table 8. Heights of oak seedlings, compared with heights of hybrid scions
grafted on stocks of the» same species (all measurements were

made in inches August 14 and 15, 1941).

lDate G r a f t s
of Seedlings
setting 1940 194-1
Stocks stocks
in No. Avg. No. Avg. No. Avg.
nursery measured height measured height measured height
Burr 1939 72 29.2 26 43.3 9 29.6
Chinese 1938 _________________ __ e 41,2 ___________, ______ __
1939 79 48.3 _________________ __ 10 31.2
Live 1938 _________________ __ 3 64.3 5 33.5
1939 8 34.4 _________________ -_ 16 30.1
Overcup _____________________ __ 1938 ____________________________________ __ 10 P 43.1
1939 1 30.0 _________________ __ 3 45.0
Post 1939 59 28.3 _________________ __ 33 33.9
F2 (Live- >< Overcup) ________ __ 1938 _________________ -_ 4 48.0 _________________ __
1939 27 37 .5 _________________ _ _ 17 39.4
F2 (Live >< Swamp White)____ 1938 _________________ -_ 37 46.2 _________________ _..
k 1939 42 31.2 _________________ __ 12 46.3

lAbout January 1 of each year.

PROPAGATION OF A RAPID GROWING SEMI-EVERGREEN HYBRID OAK 29

Some of the grafts were made on stocks set in a slightly different
location early in 1938. Where such grafts Were made on stocks of the
kind measured, height data from them is also given in Table 6, although
there are no comparable figures on seedlings.

At the time of measurement the average height of grafts made either
in 1940 or 1941 was greater than that of comparable seedlings—set in
1939——in most cases (Fig. 10). Seedling live oaks were somewhat,
but probably not significantly, taller than grafts made on such stocks
(Fig. 4). The other exception is with Chinese oaks where the seedlings
were markedly taller (Fig. 11) than the grafts on stocks of this oak.

Of the kinds of seedlings available for measurement all but the Chinese
oak have been indicated, by the evidence presented earlier in the paper,
to be good to excellent stocks for the hybrid scions. The available data
on height and grafts seems, then, to fall in line with conclusions arrived
at in previous sections of this paper.

Figure 11. Comparison of 1940 Ness Hybrid oak graft (to
the right) with a seedling Chinese oak. '.I.'he
propagation was by whip grafting on March 20,
1940. Exposure was made September 1, 1941-
Some of the branches on the right side of the
seedling were removed so as not to hide parts of
the graft. Seedlings were from January 1, 1939,
nursery planting. Compare with figures 4 and 10
where the grafts were made on stocks of the
white oak type.

General Discussion on Grafting

It would have been desirable for purposes of statistical analysis to
make the same numbe-r of insertions of the three types of grafts on each
stock used. This was the original plan, but it could not be entirely fol-
lowed for several reasons. Percentage and time of acorn germination
limited the total number of seedlings of some stocks, and in turn the
number available for certain types of grafts in other cases. Then too

30 BULLETIN NO. 612, TEXAS AGRICULTURAL EXPERIMENT STATION

the grafts were made by several persons and on different days. Hence
both the personal element and also differences in physiological responses
of the plants at difierents times (as, perhaps, witness the difference in
results with bark grafts in the 2 years) were pertinent factors. Such
factors could not very well be eliminated and while present were bound
to affect the outcome. It appears, however, that the results are clean
cut enough to recommend definitely the types of grafts and the kinds
of stocks to be used t0 secure practical success, at least initially, in
propagating the hybrid oaks. As a coro1lary—the results also show some
stocks, and perhaps one grafting method to avoid.

The work of Armstrong (1) in grafting the live oak upon the post oak
should be mentioned. He reported 84.7 p-er cent of his bark grafts, 35
per cent of cleft grafts and 0.00 per cent of whip grafts made as being
successful. His work was carried out as an undergraduate student prob-
lem, and the data upon which the report was based were taken about
one month after the grafts were made. While 92 per c-ent of the patch
buds and 81 per cent of the chip buds placed were alive 3 weeks later,
the author pointed out that the data regarding buds was not to be relied
upon due to the small number used and the shortness of elasped time
from placement to recording of final data. Armstrong’s work gave strong
evidence, since verifi-ed by time, that the live oak will unite with, and
grow upon, the post oak.

Factors Favoring Success of Stocks

The results show that the Ness Hybrid Oaks may be successfully grafted
on white oak stocks, but that the black oak species used as stocks are
in general incompatible. Several factors may account for the difference
of results with these two groups of stocks, but probably all can be traced
to the degree of relationship existing between the scion and the stocks.

It would seem probable that the type of bark and wood in 2 and 3
year old stocks might have an effect on grafting results within each
group. Among the white oaks live, overcup, white, swamp white, and
the F2 hybrids of live >< swamp white, and live- X overcup all have thin
easily worked bark covering wood that is usually smooth. Post oak,
however, while having similar bark, has underlying wood that is quite
wavy and irregular in outline. If undulating wood has an unfavorable
effect on grafting success with this species, however, it is not shown
in the ,first year’s- results. Burr oak has smooth bark the first year,
but not many seedlings are large enough for grafting then.
years it has very rough bark, covering irregularly outlined wood——a
discouraging combination especially for bark grafting. Among the black

oaks we find Chinese oak with very thick bark containing heavy con- i

ducting vessels and covering rough wood, and at the other extreme the
water oaks with thin pliable bark covering smooth wood. Ease of graft-
ing is certainly influenced by the type of bark and wood encountered,
and this is very likely to be reflected in the percentage of successful grafts
secured.

In later 3

i;

‘a
Z4

I

4
1
3
3

Bmmmummum--. n“..-

PROPAGATION OF A RAPID GROWING SEMI-EVER-GREEN HYBRID OAK 31

There are differences in the hardness or toughness of wood of the
different stocks. Chinese oak for instance has a very hard wood difficult
to cut in even planes. Burr oak wood on the other hand, while hard,
has a more even grain, facilitating the making of smooth surfaces.

The dividing crown encountered inlive oak seedlings makes this form
relatively unfavorable for whip grafting. The swollen part of the root
or crown above the division is usually the only underground part large
enough to be suitable, and it has a tendency to be soft, and sometimes
almost pithy——factors making the cutting of smooth planes rather dif-
ficult.

SUMMARY

1. First generation hybrid oaks produced by the late Helge Ness
from the cross of live oak >< overcup oak have characters making their
propagation and dissemination desirable. They have a rounded symmetri-
cal shape, approach the evergreenness of the live oak, the habit of the
overcup oak, and have a higher growth rate than either parent.

2. A wide series of treatments of cuttings from the original 30-year
old hybrids has given negative rooting results.

3. T-budding, on several stocks, has not been a successful means of
propagation.

4. Whip and bark grafting, on compatible stocks, have been success-

ful methods to date.

5. Cleft grafts have been less successful probably due to the difii-
culty of getting good fits with large caliber wood.

6. Species of oaks may apparently be arranged in two groups rela-
tive to their value as stocks.

(a) One group includes‘ the following species and hybrids belong-
ing to the “white oak” group: burr, live, overcup, post, swamp,
white, F2 (live >< overcup), and F2 (live >< swamp white).
Eighty-four per cent of all whip and bark grafts made on
these species have grown. All successful grafts apparently
made strong substantial unions, and the scions made vigor-
ous growth.

(b) The other group includes Chinese, water, black jack, and other
“black oak” forms (species). These are not promising as
stocks for the Ness Hybrids.

t“

?°*‘.°’.°‘

10.
11.
13.
14.

l5.
16.
17.

BULLETIN NO. 612, TEXAS AGRICULTURAL EXPERIMENT STATION

REFERENCES

Armstrong, W. D. 1929. The grafting of live oak upon post oak. Unpub-
lished thesis, Library of Dept. of Hort., Texas A. & M. College, College
Station, Texas.

Bailey, L. H. 1927. The standard cyclopedia of horticulture.
III, DD. 2880-2891. MacMi1lan Co.

Corlgatt,  C. 1902. The propagation of plants. U. S. D. A. Farmers’

u

Flory, ‘W. S. 1937-1939. Hybrid oak propagation (stem c tings oot
ggtgizflgs, T-buds). Texas Agri. Exp. Sta. Ann. Rpts. 39;@29;

——————— and F. R, Brison. 40-1941. Hybrid oak propagation
Texas Agri. Exp. Sta. Ann. Rpts. t 3:29; 54: (in press).

Quercus".

, and S. H. Yarnell. 6. Hybrf ak propagation (Stem
cuttings). Texas Agri. Exp. Sta. Ann. Rpt. (49;.§7-38.
Gardner, F. E. 1929. The relationship between ree age and the rooting
of cuttings. Proc. Am. Soc. Hort. Sci. 26:101-104.

Stimulation of root growth

Hutchings, G. C., and J. A. Larson. 1929-1931.
Proc. Iowa Acad. S‘ci. 36:191-

gaiocuttings from hardwood forest trees.

McGinnis, N. M. 1942.
A. and M. College.

Nesg, 216% 2618918. Hybrids of the live oak and overcup oak. Jour. Hered.

———i————, 1937. Possibilities of hybrid oaks. Joun. Hered. 18:381-386-

Reed. C. A. 1926. Nut-Tree Propagation. U. S. D. A. Farmers’ Bul. 1501.

Rehder, A. 1940. Manual of cultivated trees and shrubs. Revised Ed.
Macmillan Co.

Romberg, L. D., and C. L. Smith. 1938.
in the rooting of transplanted pecan trees.
36:161-170.

Thimann, K. V., and A. L. Delisle. 1939.
difficult plants. Jour. Arnold Arb. 203116-36;

Went, F. W., J. Bonner, and G. C. Warner. 1938.
ing of cuttings. Science 87:170-171.

Yarnell. S. H. 1933. Inheritance in an oak species hybrid.
Arb. 14:68-75.

(Personal Communication.) Landscape Art Dept,

Effects of indole-3-butyric acid
Proc. Amer. Soc. Hort. Sci.

The vegetative propagation of
(4 plates).
Aneurin and the root-

Jour. Arnold

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