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Luther Burbank

HIS METHODS AND DISCOVERIES AND
THEIR PRACTICAL APPLICATION

PREPARED FROM

fflS ORIGINAL FIELD NOTES

COVERING MORE THAN 100,000 EXPERIMENTS

MADE DURING FORTY YEARS DEVOTED

TO PLANT IMPROVEMENT

WITH THE ASSISTANCE OF

The Luther Burbank Society

AND ITS
ENTIRE MEMBERSHIP

UNDER THE EDITORIAL DIRECTION OF

John Whitson and Robert John

AND

Henry Smith Williams, M. D., LL. D.

Volume XI

ILLUSTRATED WITH

105 DIRECT COLOR PHOTOGRAPH PRINTS PRODUCED BY A

NEW PROCESS DEVISED AND PERFECTED FOR

USE IN THESE VOLUMES

NEW YORK AND LONDON

LUTHER BURBANK PRESS

MCMXV

Copyright, 1915, by

The Luther Burbank Society

Entered at Stationers' Hall, London
All righta reserved

Volume XI— By Chapters

Foreword Page 3

Nuts as a
Profitable Crop

— The Business Side of m

Nut Growing , I

II The Paper Shell, and
Other Walnuts

— The Methods Used to

Produce Them

35

III The Almond — and
Its Improvement

— Can It Be Grown Inside sn

of the Peach? DO

IV The Chestnut — Bearing Nuts
at Six Months

— A Tree Which Responds ^vr

to Education " J

V The Hickory Nut, and
Other Nuts

— Improvements Which Have Been Wrought — 191

and Some Suggestions J.DX

YJ On Growing Trees
for Lumber

— Ideas on Profitable . - r

Reforestration . . . J.DD

YII The Production of a

Quick-growing Walnut

— The Burbank Royal and 111 'J

Other Experiments J..7t)

YIU Trees Whose Products are
Useful Substances

— From the Sugar Maple to the OQO

Turpentine Tree ■LiSy

JX Trees and Shrubs for Shade
and Ornament

— Some Miscellaneous 071

Tree Experiments ib I X

List of Direct Color Photograph Prints 305

?*

XJBBABT OP
K. a STATE COLO*®

Foreword to Volume XI

Mr. Burbank begins this, his eleventh volume,
with a chapter, which, to the majority of readers,
must be novel, describing, as it does, the business
side of raising nut crops. He continues throughout
the range of profitable nuts, discussing the paper-
shell and other walnuts, the almond, the chestnut,
the hickory and a miscellaneous company of other
nuts — with many definite suggestions for improve-
ment.

He tells, also, in this volume, the method
employed to produce in twelve years a walnut
tree such as nature takes seventy years to produce;
he gives his ideas on how reforestration may be
accomplished profitably; he describes each class
of tree which yields us gums and syrups, and con-
cludes with a practical chapter on trees and shrubs
for shade and ornamentation, together with a
number of new tree experiments which offer
encouragement.

THE EDITORS.

A Dwarf Chestnut Tree

This bush-like tree is a fine example of a Burbank hybrid

chestnut. The workman who stands beside the tree is five feet

seven inches tall. Note the abundant crop of nuts on the tree and

under the tree. Gathering chestnuts becomes a simple

matter when the trees are of this type.

Nuts as a Profitable
Crop

The Business Side of Nut Growing

A CHESTNUT bush!" exclaimed a visitor;
"that is the greatest marvel I have seen yet.
I was brought up under chestnut trees; but
when I see chestnuts growing on huckleberry
bushes I am certainly having a new experience."

And I suppose this experience would be new
to almost anyone who has not visited my experi-
ment farm at Sebastopol. For, so far as I know,
until very recently, there have been no chestnuts
growing on bushes anywhere else in the world.
But there are plenty of them in my orchard at
Sebastopol; that is to say, if a sprig of a shrub
only three feet or so in height and three feet across
is entitled to be called a bush.

Moreover the nuts that are borne on these
miniature trees are of the finest variety — large,
plump nuts, at least as large as half a dozen of the
nuts you are likely to find growing on chestnut

[Volume XI — Chapter I]

J|. C. Sl««« CoW«*

LUTHER BURBANK

trees of the largest size; and they are sweet in
flavor.

The manner of development of these anoma-
lous dwarf chestnuts will be detailed in a later
chapter. Here I refer to them only by way of
introduction to suggest one of several modifica-
tions in the growing of nut bearing trees that have
been brought about within recent years and that,
jointly, are placing the industry of nut growing on
a new basis.

If it is added that some varieties of the new
chestnuts bear when only six months old, when
grown from seed — rivaling corn or wheat, and
seeming quite to forget the traditions of their own
tribe — a further glimpse will be given of the
modification that scientific plant development has
wrought in the status of the nut bearing tree.

No other tree, to be sure, quite rivals the chest-
nut in this regard; but some of the new walnuts
bear at eighteen months of age, which is quite
remarkable enough. And in general the time of
bearing of these nuts has been so hastened that the
growing of a walnut orchard to-day is an alto-
gether different matter from what it was a genera-
tion ago.

Moreover, a way has been found to induce the
walnut tree to grow about ten times as fast as it
formerly did; and the wood of the tree is of the

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LUTHER BURBANK

finest quality for the use of lumbermen and cabi-
net-makers. Of course the latter fact is of inci-
dental interest only to the grower of nuts; yet it is
not quite a negligible factor. And, from another
standpoint, obviously, the wood-producing capaci-
ties of the new trees have a high degree of
importance.

These and a few other transformations in the
nut bearing trees, brought about by careful select-
ive breeding, have, as I said, prepared the way for
an entire change of attitude of the horticulturist
toward the question of producing nuts as a busi-
ness, comparable to the business of the fruit
grower.

The Food Value of Nuts

Meantime there has been a marked change of
attitude on the part of the medical profession, and,
following them, of the general public, as to the
value of nuts in the dietary.

In point of fact, nuts have substantial merits
as food-stuffs, and these merits are yearly coming
to be more fully recognized. In the older coun-
tries, nuts have already assumed — indeed have
long held — a position of economic importance, and
convincing evidence of their growing recognition
in America is found in the reports of experiment
stations of the Agricultural Bureau, which in re-
cent years have from time to time urged the merits

[10]

ON NUT GROWING

of various nuts upon the attention of agriculturists.
A study of the market reports shows that nuts of
many kinds are handled on a commercial scale in
our cities.

There should be nothing surprising in this;
for, of course, in a wide view nuts are fruits, and
there is no obvious reason why they should not
have dietetic value. Moreover they are for the
most part grown on perennial shrubs or trees
rather than on succulent and perishable annuals,
and thus have close relationship with the fruits
of the orchard.

But the fact that nut bearing trees for the most
part receive no attention whatever from the culti-
vator of the soil, their product being gathered only
casually, has caused them to be regarded as wild
products not falling within the scope of the horti-
culturist. In most parts of the United States, in-
deed, the nut bearing trees have received no atten-
tion whatever from the cultivator of the soil, and
their product has been regarded as a more or less
superfluous luxury, rather than as having dietetic
consequence.

In the Gulf States and in California, in recent
years, there has been a radical change of attitude.
In these regions the cultivation of nuts is already
becoming an industry of importance. More re-
cently, the industry has extended to New York and

[11]

A Franquette Seedling

The walnut, like most cultivated plants, cannot be de-
pended upon to breed true from the seed. Nevertheless val-
uable trees are sometimes produced in this way. Here is a Franquette
seedling that gives good promise, and which may have
particular value for breeding experiments.

ON NUT GROWING

even to Canada. Meantime, the use of nuts on the
table in all parts of the United States has become
more and more habitual, and the shell fruits are
beginning to take their proper place among the
important products of the soil. Their recognition
as really valuable foods is so comparatively recent,
however, that it would not be superfluous to briefly
run over the list of commercial nuts, with refer-
ence to their food values and their present and
prospective economic importance.

Such an outline may advantageously prepare
the way for the detailed account of the experi-
mental work through which new varieties of sev-
eral of the more important nuts have been
developed.

The Chief Marketable Nuts

The marketable nuts include almonds, Brazil
nuts, filberts, hickory nuts, pecans, Persian or
English walnuts, chestnuts, butternuts, walnuts,
pine nuts, peanuts, and cocoanuts, not to mention
several less known and little used species.

The cocoanut, the fruit of a palm tree, is
indigenous to tropical and sub-tropical regions,
and may very likely have played a part in the
history of developing man not unlike that ascribed
to the date and the fig. It is still a most important
article of diet to inhabitants of tropical islands,
being prized not merely for the meat of the nut

[13]

LUTHER BURBANK

but for the milky fluid which it secretes in large
quantity. The natives sacrifice the partially ripe
nut for the sake of the milk, but most northerners
find this a taste to be acquired with some effort.

The meat of the ripe nut, as it comes to the
northern market, is extremely palatable, and in a
dried state, grated, it is widely employed to flavor
sundry delicacies.

The cocoanut is raised extensively in Cuba, and
to a limited extent in Florida, the total number of
these nuts produced in the United States in 1899
being 145,000.

Most of the other nuts are similarly used as
accessories of diet, for variety rather than as sub-
stantials. They are capable, however, of playing
a more important role, as the chemical analysis of
their constituents shows that they are in the main
highly concentrated foods, having little waste
aside from the shells. They contain all the import-
ant constituents of diet — proteins, fats, and carbo-
hydrates— and are thus in themselves capable of
sustaining life. They do not contain the various
elements in proper proportion, however, to make
them suitable for an exclusive diet. Moreover,
their highly concentrated character makes them
somewhat difficult of digestion if taken in large
quantities.

The chestnut differs from the other nuts in

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LUTHER BURBANK

having a relatively high percentage of starchy
matter, 42 per cent of its edible portion being
found in the carbohydrate division — a proportion
which no other nut except the acorn approaches.
The amount of fat in the chestnut is proportion-
ately small — only about 5^ per cent., as against
the 64.4 per cent, of the English walnut and the
71.2 per cent, of the pecan.

As to protein — muscle-forming matter — the
chestnut has but a little over 6 per cent., while the
English walnut has 16.7 per cent., and the Ameri-
can black walnut and the butternut head the list
with 27.6 per cent, and 27.9 per cent, respectively.

Chestnuts when fresh have a very much higher
percentage of water than other nuts — no less than
45 per cent., whereas the generality of nuts have
but three to five per cent.

It appears, then, that the meat of the chestnut
furnishes a less concentrated food than other nuts
supply, and one that is rich in digestible starches,
of which it contains six or seven times the propor-
tion common to other nuts. This excess of starchy
constituents explains why the chestnut is not gen-
erally relished so much as many other nuts in the
raw state. But it explains also why this nut may
be eaten in large quantities when cooked.

In France and in Italy chestnuts are very
generally eaten, usually being prepared by boiling,

[16]

ON NUT GROWING

and they constitute a really significant item in the
dietary of the poorer classes. Large quantities of
the nuts are also dried and ground to a flour, which
keeps for some time without deteriorating, and
from which sweet and nutritious cakes are made.
It is said that in Korea the chestnut takes a place
in the dietary not unlike that which the potato
occupies with us, being used raw, boiled, roasted,
or cooked with meat.

Production and Value of Nuts

Until the chestnut blight came in very recent
years, threatening the entire growth of chestnut
trees in the Northeastern United States, there
seemed a good prospect that the cultivation of this
nut would become an important industry in the
near future.

Details as to the blight and the probable out-
come will be considered in another connection.
Meantime, there is no present indication that the
other nuts indigenous to the northern parts of the
United States are likely to be extensively culti-
vated until they have profited by the experiments
of the plant developer. The thick shells of hickory
nuts and butternuts, and of the native walnuts,
interfere with their commercial value. We shall
consider in another connection the possibility of
remedying these defects, but for the moment the
nuts that are grown on a commercial scale are

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ON NUT GROWING

solely those that will flourish in the warmer cli-
mates, and hence the industries associated with
their production are confined mostly to the Gulf
States and to the Pacific Coast.

To be sure, the aggregate wild nut crop of the
Central and Northern States represents a consid-
erable value. But no official estimate has been
made as to the precise figures involved. In general,
the nuts obtained from such trees are not looked
upon as a commercial crop. They are for the most
part consumed on the farm or in neighboring
villages.

Only three kinds of nuts are grown on a
commercial scale in the United States at the pres-
ent time, these being, in the order of their
productivity, the Persian or English walnut, the
Pecan, and the Almond.

According to the official reports of the Census
Bureau, the total nut crop reported for 1909 was
62,328,000 pounds. This was 55.7 per cent, greater
than the crop reported for 1899, and the value,
$4,448,000, was 128.1 per cent greater. "California
is by far the most important state in the production
of nuts, and Texas ranks next. No other state
reported as much as $100,000 worth of nuts in
1909."

The Census Report takes note of nuts other
than the three just named, but the total value of

[19]

LUTHER BURBANK

all the others is relatively insignificant, the com-
bined value of the Persian walnuts, pecans, and
almonds, amounting to $3,981,000, or about nine-
tenths of the total for all nuts.

Perhaps the most interesting feature of the
report on the production of nuts is the very rapid
increase in recent years. The crop of Persian or
English walnuts in 1909, for example, was more
than twice as great as that ten years earlier. The
production of pecans in 1909 was more than three
times as great as in 1899. The production of
almonds, on the other hand, had decreased some-
what in the decade under consideration.

As to the actual number of trees under cultiva-
tion, the almond heads the list, the trees in bearing
in 1910 numbering 1,187,962, and young trees not
in bearing numbering 389,575. By far the greater
number of these are in California, which has
1,166,730 almond trees in bearing, whereas Ari-
zona, the second state, has only 6,639, and all other
states combined have only 14,593. The total pro-
duction of almonds in 1909 was 6,793,539 pounds,
with a value of $711,970.

The almond is a native of western Asia, and
has been cultivated from time immemorial. It is
mentioned in the Scriptures as one of the chief
products of the land of Canaan. In California it
has been more or less under cultivation since about

[20]

A Comparison of Leaves

At the left, a specimen of the Franquette variety of Per-
sian walnut; at the right a specimen of the black walnut. By
hybridizing the Persian and the black walnuts, Mr. Burbank produced
his remarkable Pai-adox walnut.

LUTHER BURBANK

1853. The best manner of its cultivation, however,
was not well understood, and the greater ease and
certainty with which the walnut can be grown has
led to the abandonment in recent years of many
of the almond orchards.

Nevertheless the crop is one of considerable
importance, as the figures just given show.

The total number of Persian or English walnut
trees in bearing in 1910 numbered 914,270, of
which all but about sixty thousand are in Cali-
fornia. The rapid increase of the industry, and its
prospect of still greater increase in the near future,
is shown in the fact that the number of young
trees, not yet of bearing age, was reported in 1910
as 806,413.

The extension of the industry is shown also in
the fact that of the trees not yet in bearing no
fewer than 177,004 are in the single state of Ore-
gon, and 5,513 in Mississippi. These figures fore-
cast the spread of industry to meet the growing
demand for walnuts in America.

The total production of Persian walnuts in 1909
was 22,026,524 pounds, with a valuation of
$2,297,336.

It will thus be seen that the walnut takes rank
as a commercial crop of genuine importance. The
value of the crop approaches that of the total crop
of apricots, although not as yet approaching the

[22]

The Paper Shell on the Tree

In the course of his experiments, Mr. Burbank produced

walnuts that were almost devoid of shell, but this proved a

disadvantage as the birds soon learned the secret. It was necessary,

therefore, to select specimens with thin shells, instead of those

with no shells, to continue the experiment. The

ones here shown have shells of ideal thickness.

*f

LUTHER BURBANK

j£* £ value of the half dozen more popular orchard

3f 5sf fruits.

5? O The Cultivation of the Pecan

K, ^ In 1899 the pecan ranked third among nut-pro-

gc c§ ducing trees, both as regards number of trees

& t ; under cultivation and actual product. The pecan

trees in bearing at that time numbered 643,292,

with a net product of 3,206,850 pounds.

In the ten succeeding years the pecan industry
came ahead very rapidly, and in 1910 the pecan
was second to the almond as to number of trees in
bearing, and second to the Persian walnut as to
poundage and value of its crop. Moreover, the
number of pecan trees under cultivation, but not
yet of bearing age in 1910, was actually larger than
the number of trees in bearing; showing a sur-
prisingly rapid increase of the industry.

The actual number of pecan trees in bearing
in 1910 was 1,619,521, and the number of young
trees under cultivation 1,685,066, making a total
of 3,304,587, a number in excess of the combined
numbers of almond and Persian walnut trees
under cultivation.

The production of pecans in 1909 was 9,890,769
pounds, with a value of $971,596. The total pro-
duction of 1899 was only 3,206,850 pounds. Thus,
as already noted, the production increased by
more than three hundred per cent in ten years.

[24]

The Burbank Tree Baler

This ts a modified saw-buck, devised by Mr.

Burbank to aid in packing trees for shipment to different

localities. The succeeding picture shows how the apparatus ts used.

LUTHER BURBANK

There seems every prospect that the increase will
be still more rapid in the coming decade.

Peculiar interest attaches to the pecan because
it is the one nut indigenous to the United States
among those that at present have actual commer-
cial importance. The pecan, indeed, must be
looked to as now holding the position in the south-
ern portions of the United States that the chestnut
should occupy in the northern — that of premier
nut. In recent years its merits have begun to
receive wide attention, as the figures just quoted
show, and the cultivation of pecan nuts for the
market is likely to become a really important
industry. Already there are numerous named
varieties on the market, each having its champions.

These varieties have peculiar interest because
of the fact that each one of them represents not
an artificially developed product as in the case
of most varieties of fruits and grains, but merely
the progeny of an individual tree.

It appears that here and there, particularly in
the state of Mississippi, there has grown a pecan
tree of unknown antecedents that became locally
famous for the large size and unusual quality of
its fruit.

These trees, it will be understood, are all of
one species, and the nuts are obviously all of one
kind; no one would think of mistaking any one

[26]

ON NUT GROWING

of them for anything but a pecan. Yet the indi-
viduality— the personality — of each tree is re-
vealed in the average character as to size, shape,
and peculiarities of shell and kernel, of its fruit,
and also as to great difference in productiveness
and earliness or lateness of bearing.

The Varieties of Pecan Nuts

Of course such individuality is precisely what
we have become accustomed to expect in orchard
fruits and other plants under cultivation. But
until recently it has not been generally understood
that such diversity is commonly to be found among
wild plants. So the case of the pecan furnishes an
interesting illustration of the variation of plants
in the wild state. The pecan trees that show these
individual variations are precisely like the culti-
vated varieties of orchard fruits in that they do
not breed true from seed. Doubtless it might be
possible to develop true botanical varieties from
each of them by selective breeding, but this is not
necessary any more than in the case of orchard
fruits. For, like other trees, the pecan may be
propagated by grafting or budding.

Nothing more is necessary than to make cut-
tings of twigs or buds from the parent stock, graft-
ing these as cions on an ordinary pecan stock, to
produce new trees in indefinite numbers, all of
which retain the precise quality of the parent.

[27]

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ON NUT GROWING

Such grafts were made in the case of each of
a score or so of the famous individual pecans
above referred to, with the result that as many
varieties have been given assured permanency.
For the most part, these varieties have been named
after the location where the parent tree grew, as
the San Saba, the Rome; or else after the original
owner of an early cultivator, as the Jewett, the
Pabst, the Post, the Russell, the Stuart.

According to a recent report of the Department
of Agriculture, there are ten of these varieties that
have now been advertised and propagated for a
sufficient time to gain wide distribution.

Extensive orchards of pecans are now under
cultivation in almost all of the southern states;
yet the industry is so recent that, with a single
exception, the parent trees of all the ten promi-
nent varieties are still alive and in a more or less
vigorous condition of bearing.

Unfortunately the pecan is restricted as to hab-
itat, but it flourishes as far north as St. Louis in
the Mississippi Valley, in all the gulf states, includ-
ing Texas, and along the south Atlantic seaboard.
Texas is the chief producer (5,832,367 pounds in
1909), Oklahoma second (894,172 pounds), and
Louisiana third (723,578 pounds). Quite possibly
hardier varieties, which may be grown farther
north, may in time be developed.

[29]

LUTHER BURBANK

Meantime it is held with reason that within the
territory to which it is naturally adapted, no other
nut, native or foreign, can be considered to com-
pete with it.

The qualities of the pecan as a desert ana con-
fectioners' nut are familiar to everyone; but the
best varieties have hitherto been raised in re-
stricted quantities, and hence have not found their
way extensively into the northern markets. With
the increase of the industry to commercial pro-
portions, this defect will soon be remedied, and
the pecan may be expected to advance rapidly in
popular favor. But for that matter, the demand
already greatly exceeds the supply.

Other Native Possibilities

Observation of the deferred recognition of the
merits of the pecan suggests the inquiry as to
whether there may not be other indigenous nuts
that have similarly been ignored.

It may well be doubted whether there is an-
other of comparable merit, but there is at least
one neglected one that the amateur at any rate
might find worthy of attention, whatever its de-
fects from a commercial standpoint. This is the
familiar hazelnut, a near relative of the European
filbert. The hazel-nut is smaller than its European
cousin, but it is doubtless susceptible of improve-
ment in that regard; and the hardy nature of the

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LUTHER BURBANK

shrub makes it suitable for waste lands, or as an
adjunct to the chestnut orchard, even far to the
north.

The hickory, the black walnut, and the butter-
nut, already referred to as of doubtful commer-
cial value, are nuts that may well appeal more
confidently to the amateur. They grow wild in
many regions of the Middle West where the chest-
nut is not indigenous, and the black walnut and
hickory in particular are widely famed for their
lumber — or were before the vandelism of the early
settlers practically exhausted the supply. As to
palatability, there are many persons who would be
disposed to place the butternut at the very head of
the list of edible nuts; and no one will deny the
toothsomeness of hickories and black walnuts.

All in all, the opportunity for diversion and
profit in this unexplored direction seems pecul-
iarly inviting; and it is one that is likely to be
eagerly seized by an increasing number of votaries
as the years go by. The fact that nut-bearing trees
add permanent beauty to the landscape gives them
an additional claim on the interest of that growing
body of city dwellers who are nowadays harking
back to the soil for aesthetic rather than for com-
mercial reasons. Meantime the further fact that
an unfruitful tree may ultimately be valuable as
lumber should make additional appeal to those

[32]

ON NUT GROWING

nature-lovers who, though calling themselves ama-
teurs, like none the less to have their hobbies bring
them a certain monetary return.

— In general, the nut bearing
trees have received no at-
tention whatever from the
cultivator of the soil, and
their product has been falsely
regarded as a more or less
superfluous luxury, rather
than as having valuable
dietetic importance.

Santa Rosa Nut Meats

In developing the Santa Rosa walnut Mr. Burbank had in

mind not merely thinness of shell and abundant bearing, but

also the various qualities of meat that are desirable. Among other

things, he eliminated the superfluous tannin, which gives the

nut a disagreeable astringency as well as brownish color.

The whiteness of the meats of the Santa Rosa is

evidence of his success in this regard.

The Paper-Shell and
Other Walnuts

The Method Used to Produce Them

THE fact that more than 13,000 tons of wal-
nuts are now raised annually in California,
chiefly for shipment to the Eastern mar-
kets, as against 2300 tons raised in the year 1895,
suggests, better than any amount of commentary,
the growth of this new industry.

Part, at least, of the increased popularity of the
walnut may be ascribed to the introduction of
varieties having thin shells. All Persian, or so-
called English, walnuts have relatively thin shells
as compared with the American walnuts, but the
production of the "paper-shell" varieties puts these
nuts in a class quite by themselves.

And this matter of the shell is one of real sig-
nificance from the standpoint of the consumer. A
nut like the American walnut, which can be
cracked with difficulty, requiring the use of a ham-
mer, can never gain great popularity. The diffi-

[Volume XI — Chapter II]

LUTHER BURBANK

culties encountered in extracting the meat of the
nut are too great. Contrariwise, a nut that has a
shell so thin that it can easily be crushed in the
fingers is sure to make its way and to be found
more and more generally on the dinner-table.

The terms "paper-shell" and "soft-shell" as
applied to the walnut are interchangeable. There
are now several varieties of walnuts on the mar-
ket that are generally classified under one head
or the other. Their name merely refers to the ease
with which the nut can be cracked. As to this there
is great variation among ordinary walnuts, and
the soft-shell varieties also show a good deal of
diversity. But the best varieties are so friable that
they can readily be crushed in the fingers.

In point of fact, the walnut is so variable that
it is possible for the plant developer to consult
his own wishes in the matter of modifying its
shell. I have developed a variety in which the
shell became so soft that it could readily be pene-
trated by the bills of birds; in fact a nut that had
a mere rim of shell, being thus comparable to the
stoneless plum. There would be no difficulty in
maintaining this variety of shell-less walnuts, but
its thinness of shell was a disadvantage, and I
found it desirable to breed the variety back to a
somewhat thicker shell covering, by striking a
compromise between the old hard-shell varieties

[36]

ON PAPER-SHELL WALNUTS

and a nut that was practically without a protecting
shell.

One of the thin-shelled new walnuts was intro-
duced under the name of the Santa Rosa Soft-
Shell. It was produced by the usual method of
selective breeding, and in producing it of course
other qualities were in mind besides the thinness
of shell. In particular, selection was made for
early and abundant bearing, whiteness and pal-
atability of meat, and absence of tannin — it being
tannin which gives the brown color and bitter
taste to the older or ordinary walnuts. The per-
fected Santa Rosa may be depended upon to give
more than twice as large a crop as the best speci-
mens of the France variety of walnuts, known as
the Franquette.

It should be explained, however, that there are
two varieties of the Santa Rosa Soft-Shell. One
blooms with the ordinary walnut trees, while the
other, like the Franquette, blooms two weeks later,
generally escaping the frosts that sometimes affect
the early bloomer. In producing the new soft-
shell, I inspected nuts of the ordinary walnut from
many sources. There is great variation among
these nuts, and I found some that were almost
entirely without shells. One seedling had nuts
with the meats half exposed; that is, with shell
covering a portion of its surface, suggesting the

[37]

LUTHER BURBANK

abortive stone of the little French plum from
which my race of stoneless plums was developed.

By selection among the seedlings of this almost
shell-less walnut, I discovered that a walnut with-
out any shell, bearing simply a husk, could readily
be produced. But, as I have just related, the birds
were soon aware of my secret, and they taught me
that, except for its scientific interest, the shell-less
walnut had no value.

After that the experiment in walnut breeding
was carried on in a different direction, a shell
being obviously desirable. In due time I devel-
oped two varieties that had the shell of just the
right consistency; combining this trait with the
habit of early and abundant bearing and excellent
quality of the nuts themselves.

Cions from these trees, grafted and regrafted,
make up the race of true Santa Rosa Soft-Shells.
I am informed, however, that trees grown from
the seed have been extensively sold as Santa Rosa
Soft-Shells, although they may depart very widely
from the characteristics of the parent form. In
point of fact, the name cannot be applied with
propriety to any trees except those that are grown
from cuttings, for the walnut is a variable tree and
cannot be depended upon to come true from the
seed.

^"e original Santa Rosa Soft-Shell, however,

[38]

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LUTHER BURBANK

was grown from seed, and of course it was neces-
sary in perfecting the varieties to grow successive
generations in the same way.

The parent tree was a walnut growing in San
Francisco. It bore the most valuable nuts of the
kind that had even been seen in California. Mr.
Alfred Wright first called my attention to this tree
about twenty years ago. I found that it bore not
only abundantly but regularly, and that the nuts
were of exceedingly fine quality, and of relatively
thin shell, their chief fault being that the two
halves would sometimes separate slightly, leaving
the meat exposed to the air, so that the meat did
not keep as well as if in a thoroughly sealed shell.

The original tree was destroyed soon after my
attention was called to it, to make room for a
street, but I had secured nuts and had a colony of
seedlings under inspection. Among these there
was a great variation, giving me good opportunity
for selection. Selection being made with refer-
ence to all the desirable qualities of the walnut,
in addition to thinness of shell, I presently devel-
oped a variety that seemed worthy of introduction,
and cions and trees from this were sent out under
the name of the Santa Rosa Soft-Shell.

The nuts of this variety are of medium size,
and they ripen about three weeks earlier than any
other walnuts grown in the state. The meat is

[40]

ON PAPER-SHELL WALNUTS

white and most delicious of flavor. The thin shell
is also white. The tree bears enormous crops, and
about its only defect is that it may, on occasion, be
caught by the late spring frosts. But even with
this defect, it produces a larger crop of nuts than
any other tree that I have seen.

Hybridizing With the Japanese Walnut

The experiments in which I hybridized the Per-
sian Walnut with the California Black Walnut,
producing the tree named the Paradox, have been
outlined in an earlier chapter, and will be referred
to again in a later one.

It will be recalled that this tree has extraordi-
nary qualities of growth, but that it is almost ster-
ile, producing only a few nuts on an entire tree,
and these nuts of the poorest quality.

Another hybridizing experiment that had great
interest was that in which the Persian Walnut was
crossed with the Japanese walnut, known as Jug-
lans Sieboldii. The Persian walnut in these crosses
was used as the pistillate parent.

The first generation hybrids of this cross show
a combination of qualities of the two parent spe-
cies as regards the nuts, which are not borne abun-
dantly. The foliage is much larger, however, than
that of either species, the bark is white, and the
tree itself is of enormously enhanced growth. It
probably makes about twice as much wood in a

[41]

Trunk of the Franqnette Walnut

The Franquette is a specialized variety of the Persian wal-
nut that is particularly prized in California because of its cer-
tain bearing. Note the smooth white bark of this tree in contrast
with the rough black bark of the black walnut
shown in the succeeding picture.

ON PAPER-SHELL WALNUTS

given period as either of the parent species. The
leaves are quite hairy on both sides, even more so
than those of the Japanese parent. The branches
are inclined to droop.

The nuts of the Japanese walnut have an
exceedingly hard shell. The meat of the nut, how-
ever, is delicious, perhaps equaling that of any
other nut, with the exception of some varieties of
the pecan. But it is very difficult to get the meats
from the shell, as they are usually broken in
cracking the nut.

There is, however, a form of the Japanese wal-
nut which is so variant that it is sometimes re-
garded as a distinct species, under the name of
Juglans codriformis, but which I think not cor-
rectly entitled to this rank, inasmuch as the two
forms are closely similar as to general appearance
and growth. The chief difference is in the nuts,
which in the cordiformis are usually heart-shaped,
somewhat similar in appearance to the form of
the central chestnut where these nuts grow three
in a burr. The nut is exceedingly variable, not
only in size but in form and thinness of shell.
Some individual trees bear nuts that are six times
as large as those borne on other trees in the neigh-
borhood. The shell is much thinner than that of
the Japanese walnut, and the meat is of the same
excellent quality.

[43]

LUTHER BURBANK

I speak thus in detail of this variety of the
Japanese walnut, because its qualities are such as
to merit fuller recognition than it has hitherto re-
ceived. The tree is perhaps as hardy as the Amer-
ican black walnut; it is as easily grown, and per-
haps even less particular as to soil and climate.
The trees are very productive, especially as they
grow older. The branches droop under the weight
of the nuts. Where other walnut trees bear nuts
singly or in clusters of twos or threes, the Japanese
walnut tree bears long strings of nuts, sometimes
thirty or more in a single cluster. The nuts are
thickly set about the axils, the cluster being from
six to twelve inches in length.

Hybridizing Native Walnuts

The cross between the Persian and Japanese
walnuts, like that between the Persian and the Cal-
ifornia black walnut, did not result in producing
a tree that had exceptional value as a nut pro-
ducer. This cross, like the other, seemingly brings
together strains that are too widely separated; and
while there is a great accentuation of the tendency
to growth, so that trees of tremendous size are
produced, there is relative sterility, so that a tree
sometimes bears only a few individual nuts in a
season.

But the results were very strikingly different
as regards the matter of bearing when the Cali-

L44]

Trunk of the Black Walnut

A comparison of this picture with the preceding ones
shows the striking difference in appearance between the Persian
walnut and the American species. The two were combined, it will be
recalled, to produce Mr. Burbank's celebrated Paradox wal-
nut, illustrated in other pictures of this volume.

LUTHER BURBANK

fornia black walnut was hybridized with the black
walnut from the eastern part of the United States.
These two trees are more closely related species,
and have diverged relatively little. Doubtless the
time when they had a common ancestor is rela-
tively recent as contrasted with the period when
that common ancestor branched from the racial
stem that bore the Persian and Japanese walnuts.

Yet the differences between the walnuts of the
eastern and western parts of America are sufficient
to introduce a very strong tendency to variation.

Indeed, the result of crossing these species was
in some respects scarcely less remarkable than
that due to the crossing of the Persian walnut with
the black walnut of California.

In this case, as in the other, the hybrid tree
proved to have extraordinary capacity for growth.
Indeed, I have never been able to decide as to
which of the hybrids is the more rapid grower.
But in the matter of nut production, the discrep-
ancy was nothing less than startling. For, whereas
the first-generation paradox walnut produced, as
we have seen, only occasional nuts, the hybrid
between the two black walnuts — it was named the
Royal — proved perhaps the most productive nut
tree ever seen.

I have elsewhere cited a tree, sixteen years of
age, that produced twenty large apple boxes full

[46]

ON PAPER-SHELL WALNUTS

of the nuts in a season — so extensive a crop that I
sold more than $500 worth of nuts from this single
tree that year. And the following year I sold nuts
from another tree to the value of $1,050. The nuts
were used for seed to produce trees of the same
variety.

This extraordinary difference between the two
hybrids is doubtless to be explained by the slightly
closer affinity between the parents of the Royal.
Their relationship chanced to be precisely close
enough to introduce the greatest possible vigor
and the largest tendency to variation compatible
with fertility. The parents of the Paradox, on the
other hand, were removed one stage farther from
each other, permitting the production of offspring
of vigorous growth, but bringing them near to the
condition of infecundity. They were not abso-
lutely sterile, but their fecundity was of a very
low order.

The seedlings of the Royal hybrid vary in the
second generation, as might be expected, although
the variation in size and foliage is less than in the
case of the Paradox. The extraordinary range of
size, some of the second generation hybrids being
giants and others dwarfs, has been elsewhere re-
ferred to. It will be recalled that some of these
second generation hybrids grew to the height of
four feet in the first year, while beside them were

[47]

A Grafted Walnut Tree

The selected varieties of walnuts do not breed true from

the seeds; so it is necessary to graft them, in making commercial

orchards, just as in the case of the orchard fruits. Here is a typical

grafted specimen, growing in the back yard of Mr.

Burbank's home in Santa Rosa.

ON PAPER-SHELL WALNUTS

others that grow only six or eight inches. One
grew five hundred times as fast as another, the
nuts from which they grew having been picked
from the same tree, and planted the same day side
by side.

To make sure of securing trees having the traits
of the original Royal, it is necessary to grow the
trees from grafts either of the first generation
hybrid or a selected second generation hybrid
showing rapid growth. The number of the latter,
however, is sufficient to ensure a reasonable pro-
portion of good trees from any lot of seed; and
the Royal has been in general demand as a tree to
furnish stocks on which the Persian walnut may
be grafted.

It is found that on most soils a Persian walnut
grafted on roots of the Royal hybrid will produce
several times as large a crop as if on its own roots.
Moreover the trees under these conditions are
relatively free from the blight.

The nuts of the Royal hybrid are similar to
those of the parents, except that they are larger in
size. The very thick shell is objectionable, as
already noted. Doubtless the shell can be made
thinner by selective breeding, but no comprehen-
sive efforts in this direction have as yet been car-
ried out. The black walnut, in spite of the really
fine quality of its nut, has never become an impor-

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ON PAPER-SHELL WALNUTS

tant article of commerce. But there are great pos-
sibilities open to it if the shell could be reduced
to a condition comparable to that of the English
walnut.

The nuts borne by the Paradox are interme-
diate in form and appearance between the types
of nuts of its parents. Exteriorly they resem-
ble the Persian walnut, but the shell partakes of
the thickness and solidarity of that of the black
walnut. In at least two instances among the thou-
sands of second generation Paradox walnut trees
that have been grown, the trees produce extra,
large fine walnuts in abundance. However, both
of these are quite thick-shelled, but from their
second generation hybrid, which can be multiplied
abundantly, good, hardy, thin-shelled varieties
may be produced.

It is possible that further hybridizations, in
which the Royal and Paradox hybrids were them-
selves crossed, might result in the development
of a variety, properly selected, that would retain
the good qualities of the Persian nut, and combine
these with the size and prolific bearing of the
Royal.

Hybridizing Methods

The experiment, at any rate, is well worth try-
ing. But, of course, whoever undertakes it must
be content to make haste slowly, for the black wal-

[51]

LUTHER BURBANK

nut has not as yet been made to bear in childhood,
so to speak, as the chestnuts and some strains of
the English walnut now do. But in this regard
also there would doubtless be rapid improvement
under selection.

The actual method of hand-pollenizing is very
simple. Nothing more is necessary than to break
off the flower bearing branch, just at the right
time, and shake it over the flowers of the pistillate
parent.

Of course one cannot make sure that some of
the flowers will not be self-fertilized, but by plant-
ing a large number of the nuts, it will be possible
to determine from the appearance of the seedlings
which ones are hybrids. Also where the trees
grow close together, there are sometimes natural
hybrids, though I was not aware of this when I
made my first experiments, in years 1875-1880.

When I made my first experiments at hybrid-
izing the walnuts, I planted the seeds of the entire
tree. n the rows of seedlings, I could at once
deterr* e which ones were hybridized, as these
grew fai nore rapidly than the others, besides dif-
fering notably in general appearance.

My first experiment was made with two black
walnuts, and it was the success of this that led me
to attempt to hybridize the Persian and California
walnuts the following year. The hybridization in

[52]

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LUTHER BURBANK

which the Japanese walnut was used was made a
few seasons later. The results, as regards the pro-
duction of nuts, have been sufficiently detailed.
Up to the present no variety of commercial value
as a nut bearer has been produced, although the
indirect influence of the hybrids on the Persian
walnut industry, through their use as stocks, has
been quite notable.

The Butternuts

There is a very near relative of the black wal-
nut, known as the butternut, that was formerly
well-known in most forest regions of the eastern
United States.

The two trees are of closely similar appearance,
and the nuts have the same characteristic thick
and corrugated shell. The butternut, however, is
oval in shape, whereas the walnut is nearly round.
The meat of the butternut is also somewhat richer
in quality, and it is generally regarded as superior
in flavor. The meat itself, indeed, is by many peo-
ple regarded as superior to that of any other nut.
The difficulty is that the shell, like that of the black
walnut, is very thick, making it difficult to extract
the meat without breaking it.

The butternut thrives generally where the black
walnut does. It makes a more spreading tree, but
the wood is softer and far inferior for cabinet
purposes.

[54]

ON PAPER-SHELL WALNUTS

There is an Asiatic species, known as Juglans
Manschurica, that may be regarded as interme-
diate in form between the butternut and the black
walnut. It rather closely resembles the Japanese
walnut in general appearance, but it bears a nut
with rough surface like the butternut, and the meat
is also similar in quality and appearance to that
of the butternut, being superior to that of the black
walnut.

This tree may be said to form a connecting link
between the Japanese walnut, the American black
walnut, and the butternut. Possibly it could be
used advantageously in a hybridizing experiment
that would ultimately blend the strains of these
different species.

The Cultivation of the Walnuts

The idea of growing walnuts commercially is
one that has scarcely been thought of in the tem-
perate regions of the United States. Even in
regions of the middle and eastern states where the
English walnut will grow, it has never been culti-
vated extensively, and of course this tree is too
tender to be profitably grown in the northern
states. But the black walnut and butternut, on the
other hand, are exceedingly hardy trees, thriving
even in regions where the winters are excessively
cold.

All of these trees, however, require a deep, rich,

[55]

More Hybrid Walnuts

The nut of the Paradox walnut has the outward appear-
ance of the Persian walnut, one of its parents. The shell re-
tains, however, a good deal of the thickness of Jhe black walnut, bw
this can doubtless be modified by selective
breeding in later generations.

ON PAPER-SHELL WALNUTS

moist, loamy soil, in order to thrive. Trees that
produce wood of such extraordinary hardness of
texture, and nuts so stocked with fats and proteins,
could not be expected to draw adequate nourish-
ment from impoverished soil. In point of fact,
the black walnut and the butternut, in the regions
of the United States to which they are indigenous,
are usually found growing along the rivers, or in
rich alluvial valleys. Any idea that they could be
raised to advantage on soil that is too poor to pro-
duce ordinary crops of cereals or vegetables, is
fallacious.

At the moment, there is not demand enough
for the black walnut or the butternut to justify
the raising of these trees on a commercial scale.
It will be necessary to produce new varieties by
hybridization and selective breeding before these
nuts can be made popular. But, as I said before,
there is every reason to believe that a series of
experiments looking to the production of improved
varieties would be more than justified by the re-
sults obtained, and I shall point out in another
connection the commercial possibilities of produc-
ing lumber trees in this way that make the project
doubly attractive.

It may be well to call attention to one or two
peculiarities of the walnut that should be known
to anyone that attempts hybridizing experiments.

[57]

LUTHER BURBANK

In particular it should be understood that the
staminate flowers of the walnut usually bloom and
shed their pollen from one to four weeks before
the fruit-bearing nutlets appear.

One would naturally suppose, under these cir-
cumstances, that the pollen would all be lost and
that there could be no crop. But, in point of fact,
the pollen appears to retain its vitality for a long
time, and even where it has been shed some weeks
before the ripening of the pistillate flowers, there
may be a full crop. The hand-pollenizer must
bear in mind this tendency of the two types of
walnuts to mature their flowers at different times.
Still, as already suggested, the pollen appears to
retain its vitality, and ultimately to be able to
effect fertilization even though applied some time
before the maturation of the pistils.

In France the early spring frosts are likely to
be very destructive to the ordinary walnuts, and
the French nut raisers have come to depend largely
on the Franquette, a variety already referred to.
While this variety is in some respects inferior, it
has the one supreme quality of not blossoming
until the season of spring frosts is over. It blooms
perhaps four weeks later than ordinary varieties.
This ensures a good crop from the Franquette
variety, even in years when others have been dam-
aged by the frost, so that the average production

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LUTHER BURBANK

of this variety throughout a term of years may be
higher than that of others that in any given season
may surpass it.

There is obvious opportunity to hybridize this
variety with the other varieties of the Persian wal-
nut that blossom earlier, but produce a better crop
of nuts. Such crossing would doubtless supply
material from which races may be developed that
will retain the late blossoming habit of the Fran-
quette, combined with the nut producing qualities
of the other parent.

We have seen that a tendency to fruit late in
the season is usually correlative to a tendency to
early ripening of fruit so that late bloomers are
adapted to growth relatively far to the north. A
late blooming strain of the Franquette walnut
might furnish material for the development of a
variety of walnuts that will be hardy enough to
grow in higher altitudes than those to which the
English walnut is now limited. But for the pro-
duction of real hardy races it is probable that
hybridizing with the black walnut — the same cross
that produced the Paradox — must be looked to, to
supply the foundation for a series of experiments
in selective breeding.

The pioneer work, indeed, has been done in
the production of the Paradox walnut itself.

It may reasonably be supposed that further

[60]

ON PAPER-SHELL WALNUTS

experiments in which this hybrid is used as a
parent will lead to the development of altogether
new races of nuts that will have economic
importance.

The entire matter of the development of com-
mercial nuts has only recently begun to attract the
attention of the orchardists. There is reason to
expect that the developments of the next few gen-
erations will be comparable to the progress of the
past century in the development of orchard fruits.

— The edible nuts are destined
to occupy a far more important
place in the dietary than they
have ever had before, at all
events in the temperate zone.
And the walnut is in the
van of the new movement.

Almond Tree in Blossom

One great fault of the almond tree is that it tends to blos-
som so early in the season that its flowers are likely to be
blighted by the frosts. This makes it impossible to raise almonds
commercially in many regions where they otherwise
would thrive. Careful selective breeding will
probably overcome the defect.

The Almond and Its
Improvement

Can It Be Grown Inside of the Peach?

IN the early years of my experimenting, soon
after I began importing plants, I attempted
to cross the Japanese plum with the almond.

The cross was made without very great diffi-
culty, and the results were exceedingly interesting.
Each species was fertilized with the pollen of the
other, and here as elsewhere it appeared to make
no particular difference in which way the cross
was made.

The hybrid seedlings partook somewhat of the
character of the earliest of the hybrids produced
by crossing the plum and the apricot. Most of the
seedlings outgrew either parent, their enhanced
vigor suggesting that of the hybrid walnuts. But
on the other hand some of them almost refused to
grow at all, being permanently dwarfed, and in
this regard suggesting a certain number of the sec-
ond generation of the walnut hybrids.

[Volume XI — Chapter III]

LUTHER BURBANK

This wide diversity of form and vigor in the
first generation hybrids is a rather unusual phe-
nomenon. As a rule, we have observed that first
generation hybrids are somewhat uniform in char-
acter, and that the tendency to wide diversity ap-
pears in the second generation. Indeed, attention
has more than once been called to the fact that
the discovery that such is the tendency among
hybrids was the one that put me on the track of
most of my successful plant developments.

At the time when my experiments in hybridiz-
ing the Japanese plum and the almond were com-
menced, there were few, if any, other plant experi-
menters anywhere in the world who seemed fully
to grasp the principle that variation occurs in the
second generation, and that it is by raising large
numbers of second generation hybrids from which
to make selection, that the development of new
and useful varieties of plants may best and most
rapidly be carried out.

This principle is so familiar to-day that horti-
culturists and botanists who refer to it very com-
monly overlook the fact that the recognition of
the principle is very recent.

Twenty-five years ago I found it impossible to
convince most well known horticulturists and bot-
anists and biologists — with many of whom I had
some spirited discussions on the subject — that the

[64]

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great individual variations occur in the second
and a few succeeding generations.

To-day all these men, in common with horti-
culturists and biologists in general, acknowledge
that these variations and recombinations do occur.
Indeed, nothing more is necessary than the most
casual inspection of the new varieties that have
been developed at Santa Rosa in the intervening
period to establish the validity of what was gen-
erally regarded as an heretical view only twenty-
five years ago.

And yet the case of the first generation hybrids
between the Japanese plum and the European
almond, showing the wide diversity just recorded,
suggests that it is not always easy to lay down
rules of thumb. Observation of the phenomenon
of plant development in the field may present com-
plexities that make the sifting out of principles
difficult. No one whose first hybridizing experi-
ments happened to be performed with chance
hybrids of the plum and almond, and who saw
among his first generation seedlings all the range
of forms from dwarfs to giants, would have been
likely to conclude that the first generation hybrids
are generally uniform in character and that varia-
tion takes place in the second generation.

Looking back now, and being able to check the
observation with knowledge gained through not-

[66]

Almonds on the Stem

The picture suggests the tough leathery character of the
seed-covering that makes us the almond fruit. Unlike its allied
stone fruits, the almond has been selected for the seed itself, not for
the pulp that surrounds it. Mr. Burbank has shown that the
pulp may also be made attractive through hy-
bridizing and selection, as we shall see.

LUTHER BURBANK

ing the effect of hybridizing hundreds of other
species, it is interesting to make inquiry as to why
the first generation hybrids of the plum and
almond showed such anomalous diversity.

I am inclined to think that the answer may be
found in the assumption that either one parent
or the other was itself a hybrid. Perhaps both
parents were hybrids. The fact that almonds are
known to cross with the peach and the nectarine —
to which reference will be made more at length
presently — lends color to this assumption. And of
course there is no question that the Japanese plums
are largely hybridized. In a word, then, the
hybrids produced by cross-pollenizing the Japan-
ese plum and the almond were probably in reality
second generation hybrids having the strains of
other species than the almond and the Japanese
plum in their veins.

Be this as it may, the facts as to the curious
diversity among the plum-almond hybrids have
more than passing interest.

It should further be recorded that the diversity
in size was matched by the wide range of diversity
in minor characteristics. The bark and leaves
varied extensively among the different hybrids;
on some trees the buds were round and plump,
and on others long and sharp. Many of the trees
produced somewhat abundant blossoms, and the

[68]

ON THE ALMOND

individual blossoms varied widely in color and in
size.

But there were other trees that produced no
blossoms whatever under any circumstances.

These would form great clusters of buds, but
instead of bursting into flowers the buds would
drop off and ordinary branches would come out
in their stead.

In the case of buds already opened to form
flowers, the blossoms not only varied as to size
and color, but they showed the most astonishing
diversity as to their essential fructifying organs.
Some of the blossoms had numerous pistils and
no stamens. Others had numerous stamens and
no pistils. In yet other cases there were blossoms
having stamens and pistils but absolutely without
petals.

In no case was fruit formed. The blossoms one
and all were sterile.

An attempt was made to fructify the blossoms
by pollenizing them with pollen from each of the
parents. But the effort was futile. The ovaries
were seemingly incapable of maturing.

It would appear, then, that the Japanese plum
and the almond, as represented by the particular
specimens that were used in these hybridizing
experiments, were just at the limits of affinity that
permitted cross-fertilization, but imposed sterility

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ON THE ALMOND

on the offspring. The parents were a shade more
widely removed from each other genetically than
were, for example, the plum and the apricot or
the Persian and California walnuts.

Conceivably this fact, and not the mixed ances-
try of either parent, may have accounted for the
diversity of form of the progeny.

As the plum-almond hybrids were sterile, it is
obvious that the experiments through which I had
hoped to develop new varieties and perhaps new
species of fruits could go no further in this direc-
tion. It is of course possible that individual plums
and almonds or different varieties of the two races
might be found that would combine to produce
fertile offspring. This supposition finds support
in the fact that my earliest crosses between the
plum and the apricot were also sterile; whereas
later ones produced the fertile plumcot, as the
reader is aware.

So it is obviously worth while to continue the
experiments of hybridizing the plum and the
almond, and there is every reason to hope that
interesting and valuable results may be attained.

My own experiments, however, although they
have been repeated occasionally and have never
been quite lost sight of during the twenty-five years
that have intervened since the first tests were
made, have produced only the anomalous results

[71]

LUTHER BURBANK

just related. Yet even these, in addition to their
scientific interest, may be thought to point the
way to more practical developments.

At least they prove that there is no barrier
between the tribe of plums and the tribe of
almonds that may not be partially broken down.
The Almond Crossed With Peach and Nectarine

Since the almond can be crossed with the plum
it may reasonably be expected that mating would
be effected with its closer relatives, the nectarine
and peach, with even greater facility.

And in point of fact it has been observed that
the almond crosses with the nectarine so readily
that it is practically impossible to prevent cross-
fertilization when the two trees grow in the same
neighborhood. The bees appear to visit them in-
discriminately, and to effect hybridization so com-
monly that it is impossible to raise fruit from the
seed with any degree of certainty when there has
been an opportunity for cross-fertilization. The
same thing is true, as might be expected, of the
peach; which, indeed, as we have elsewhere seen, is
scarcely separable botanically from the nectarine.

Most varieties of almond blossom very early in
the season, before nectarines or peaches are in
bloom. But where the trees are blossoming at the
same time in the same neighborhood the bees are
almost certain to mix them ind'scriminately.

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It is nothing unusual in California where
almonds and peaches are growing in the same
orchard, and where peach seeds are planted, to
have one third of the seedlings turn out to show
marked characteristics of the almond; or, contrari-
wise, to find that a number of the almond seed-
lings show the characteristics of the peach.

This, of course, is sometimes annoying to the
practical orchardist, but it suggests interesting pos-
sibilities for the plant developer.

Wishing to see just where the experiments
might lead, I have crossed the almond with the
nectarine, using great care to make sure that the
experiment was not vitiated by accidental pollen-
izing. In some cases I have used the old method
of tying a sack over the flower, which I do not
usually consider necessary in pollenizing if prop-
erly performed.

Hybridizing experiments of this type have been
carried on somewhat extensively for at least fif-
teen years. I have thus produced a hybrid
almond-nectarine that has an absolutely smooth
skin, with nothing of the roughness and comatose
condition usually found in the almond. The
hybrid reproduced the color and quality of the
flesh of the white nectarine parent as well as its
smooth skin. And as the almond quality of seed
and stone was fairly reproduced, the combination

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was a very curious one — to all intents and pur-
poses a smooth-skinned peach, with white flesh,
bearing at its core an almond nut.

Further experiments in selective breeding will
be necessary to develop the hybrid to a stage at
which its qualities of flesh and nut respectively
will give it commercial importance; but the foun-
dation for such development is supplied in the
hybrid already secured. This hybrid, it may be
noted incidentally, is a most remarkably vigorous
grower.

An allied series of experiments of equal inter-
est was inaugurated by hybridizing the Languedoc
almond and the Muir peach, using, as in the other
case, the utmost precaution to prevent foreign
pollenization.

Many seedlings were grown from this cross and
a large number of them have been under observa-
tion for years.

The most notable thing about these hybrid seed-
lings from the outset was the tendency of many
of them to take on rapid growth. Some of them
grow live or ten times as fast as the average seed-
lings of either parent. This propensity of hybrids
to rapid growth is something that we have seen
manifested in many other cases. It is, indeed, a
rather common result when species that vary by
just the right amount are hybridized. The hybrid

f76T

LUTHER BURBANK

walnuts furnished the typical illustration of this
on the most spectacular scale.

The fruit of these almond-peach hybrids varied
a good deal on different trees. Sometimes the
fruit was leathery like that of the almond, but in
other cases it was edible and quite peach-like. In
a few cases the pulp was so fully developed that
it might be considered a fairly good peach. The
seed covering was usually in the shape of an
almond and smoother, thinner, and generally more
elongated than the peach stone. It was hard-
shelled and corrugated, but had not the texture
of the peach stone. The meat within was sweet
or slightly bitter, suggesting a rather inferior
almond.

Thus the fruit of this hybrid might be said to
be fairly intermediate between the fruits of the
parents, yet on the whole the flesh of the peach
and the stone of the almond, respectively, tended
to be prepotent. This is what would perhaps be
expected, when we recall that the flesh is the spe-
cialized modern development in the case of the
peach, and that the seed is similarly specialized
and developed in the case of the almond.

We have found occasion to believe that pre-
potency or dominance is conditioned on newness
of development; the case of the peach-almond
hybrid gives a measure of support to this theory.

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But while the specific qualities of peach and
almond, representing their specialized develop-
ment in comparatively recent times, thus tend to
be segregated along Mendelian lines, yet the traits
in each case are of such long standing that they do
not Mendelize in the clear and satisfactory way
that we have seen manifested in some other cases
— for example, the color of the blackberry, and its
thorns.

There is, to be sure, a very marked segregation
in the second generation, illustrated by the most
astonishing variation among different second gen-
eration hybrids in the matter of size, rapidity of
growth, and almost every quality of flower and
fruit.

This variation was so marked, indeed, as to
rob the seedlings of the value they might other-
wise have had as stock for grafting. The large-
growing specimens have value for this purpose,
but the diversity among the seedlings is so great
that they cannot at present advantageously be
grown with any hope of producing dependable
stocks.

In the matter of the fruit, the second genera-
tion hybrids are equally variable. There are some
specimens that tend to reproduce the almond qual-
ity and others that tend to reproduce the peach
quality. And as might be expected there are yet

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others that combine the quality of the two fruits.
The best of these bear fruits that are obviously
peaches, even peaches of fair qualities, yet that
have at their center what would be at once recog-
nized as an almond nut, with characteristic shell
and seed.

In a word, these are almonds grown inside the
peach — a combination of obvious interest.

But this anomalous fruit, notwithstanding its
interest, did not present commercial possibilities
that could at the moment be realized. The peaches
that thus bear almonds are not of the best quality
as compared with recognized varieties of commer-
cial peaches. Neither, on the other hand, were the
almonds borne by these peaches of a quality to
enable them to compete in the market with the
best varieties of commercial almonds.

What had been produced, in a word, was a
rather inferior peach bearing at its core a rather
inferior almond. The combination has obvious
scientific interest, but it has no immediate com-
mercial value.

There is no reason to doubt that a continuance
of the experiment in which selection was made
among the best specimens of this hybrid fruit,
together with further hybridization in which the
strains of the best peaches and the best almonds
were successively introduced, might result in pro-

[82]

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ducing a peach-almond that would have flesh
equal to the best varieties of peaches and a nut
equal to the best almonds.

Even now there are apricots that bear delicious
nuts. Inasmuch as the apricot is already in this
condition, there is no reason why the peach should
not do the same. The apricot seeds of California
are now nearly all shipped to France to make
almond oil.

At the time when the experiments above re-
ferred to were carried out, however, it was not
clear that a fruit combining the qualities of the
peach and the almond would have great commer-
cial value. The peach industry and the almond
industry are so entirely different that the inaugu-
ration of altogether new methods would be neces-
sary to make them operable in combination.

Hence the hybridizing experiments were not
carried beyond the second generation, and the
hybrid trees were thereafter used as stocks for the
engrafting of cions that gave greater commercial
promise, even though less interesting from a scien-
tific standpoint.

A New Peach-Almond Cross

A subsequent series of experiments was under-
taken, however, to which reference has been made
in another connection, in which the almond was
combined with the purple-leafed peach.

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It has already been recorded that the first gen-
eration hybrids of this cross bore green leaves
exclusively, but that purple leaves appeared in a
certain proportion of the hybrids of the second
and subsequent generation.

In this cross, the purple-leafed peach was used
invariably as the pistillate parent. There is every
reason to suppose, however, that the results would
have been the same had the cross been made the
other way.

Among the second generation seedlings were
not only some with red leaves, but others that
6howed a combination of colors varying from the
pure green almond leaves through different shades
to the crimson leaf of the peach.

There was thus exhibited a pronounced ten-
dency to segregation of colors in certain cases,
and a combination of the colors in others.

Selection being made among the trees with the
purple leaves, this characteristic, as might have
been expected, reproduced itself, and a race of
purple-leafed peach-almonds was developed. The
fruit of this hybrid is purple fleshed, and as to its
general characteristics it is a fair compromise be-
tween the peach and the almond, not unlike the
hybrid form already described.

This form of peach-almond has considerable
merit as an ornamental tree, and it will probably

[86]

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prove of value as an acquisition for the garden
and dooryard. Even though a peach that bears
an edible seed has no greatly added commercial
value, owing to the small size of the seed, such a
fruit with large seed of thinner shell, and with
peach flavor, should certainly be appreciated.
Improving the Almond

All this has to do with the production of a
compound fruit in which the almond seed is only
an accessory. It remains to say a few words about
the almond itself as a commercial nut.

The importance of the subject will be obvious
when we record that in a recent year more than
three thousand tons of almonds were produced in
California alone. When it is further recalled that
numberless unsuccessful attempts have been made
to establish almond orchards in various warmer
regions of the United States, and that the failure
of these orchards has been due almost exclusively
to a single remedial defect, the importance of the
almond from the standpoint of the plant developer
will be more clearly understood.

The one great defect of most varieties of
almond is that they bloom so early that their blos-
soms are likely to be destroyed by frost. A second
minor defect is that many of the varieties of
almond do not bear well unless they are cross-
fertilized with pollen from other varieties.

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The later defect is obviously one that requires
only reasonable intelligence in the planting of
different varieties in contiguous rows, so that
cross-fertilization may readily take place, or the
production of varieties with perfect blossoms. To
overcome the defects due to too early blooming is
a somewhat more diflicult matter.

Fortunately, however, there is a rather wide
range of variation among different kinds of
almond as to the matter of time of blooming. It
follows that there should be no great difficulty in
producing, by selective breeding, a variety that
combines desirable qualities of nut production
with the habit of late blooming. The difficulty has
been that until recently orchardists have not rec-
ognized the possibility of thus segregating and
recombining characters, and they have "trusted to
luck" in setting out their almond orchards, so in a
large number of cases the profitless trees were cut
down or regrafted to Burbank prunes.

Latterly, the California orchardists have
learned that there are two or three varieties that
may be depended on, notably the Nonpareil and
the Ne Plus Ultra, both of which originated in Cal-
ifornia from seedlings grown by A. T. Hatch of
Salinas County. These may best be polenized, in
the opinion of experienced orchardists, by the
variety known as Texas Prolific.

[90]

ON THE ALMOND

Unfortunately neither of the varieties men-
tioned produces nuts of the largest size, but their
certainty of bearing gives them advantage over
varieties that would otherwise be superior but
which cannot be depended upon.

It should not be difficult, except that such an
experiment necessarily takes time, to crossbreed
the different varieties that have individual traits
of exceptional value, and thus to produce in the
second generation, or through successive selec-
tions, varieties that will combine the best quali-
ties. Indeed, something has already been accom-
plished in this direction, notably in the case of such
a variety as that known as Drake's Seedling, a late
blooming variety that is prolific and a regular and
abundant bearer, notwithstanding its parent
form was the Languedoc which has been pretty
generally condemned for irregular bearing. There
is no good reason why the almond should not
bear as regularly and as abundantly as the apple
or peach or cherry.

As to the shell of the almond, this has been so
specialized through selective breeding that in the
best varieties it is perhaps as soft and thin as
desirable. If it becomes too soft, it is liable to
injury in shipping, and thus the appearance of the
nuts is marred and their market value impaired;
also being subject to destruction by birds before

[91]

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ON THE ALMOND

it is harvested. Perhaps, however, selective breed-
ing may advantageously be carried out with an eye
to the whitening of the shell of the nut. At present
it is necessary to bleach the shells after the nuts
are thoroughly dried, first with low pressure steam
and then with the fumes of sulphur. Such bleach-
ing is necessary to meet the demands of the
consumers.

It would obviously cheapen production and
save a good deal of trouble if a variety could be
produced that would have the desired color of
shell in the natural state. Another defect is that
the almond tends to cling to the tree too tena-
ciously, requiring unnecessary labor. Any almond
grower would appreciate these two experiments.

My own experiments of late have been in all the
directions mentioned, and I have reason to sup-
pose that I now have better almonds than any
heretofore grown.

It is clear, then, that there are various
directions in which the almond may profit by the
attentions of the plant developer. The steady and
increasing demand for this nut warrants the
expectation that systematic efforts for its improve-
ment may meet with an adequate financial reward.
Already the cultivation of the almond is an indus-
try that exceeds in importance that of any other
nut except the walnut and pecan. And it is an

[93]

LUTHER BURBANK

industry that will increase in proportion as the
efforts of the plant developer make the almond a
more certain bearer. What has just been said will
sufficiently indicate the lines along which the plant
developer must work in order to produce these
results.

— It is obviously worth while
to continue the experiments
of hybridizing the plum and
almond, and there is every
reason to believe that
interesting and valuable
results may be attained.

The Chestnut— Bearing Nuts
at Six Months

A Tree Which Responds to Education

WHEN a boy in Massachusetts, I used to
observe the great variation among the
native American chestnuts in my
father's wood lots. Like most boys I was fond of
nuts, and in gathering them I soon learned that
there were certain trees that bore large, glossy,
rich brown nuts with sweet toothsome meats, and
that there were other trees that bore only small,
flat, ash-colored nuts of insignificant size and
inferior quality.

I observed that the trees that bore these seem-
ingly quite different nuts differed also in size and
in foliage. And I particularly noted that such
variations were not seemingly due to any local
conditions, inasmuch as the trees bearing fine nuts
and those bearing poor ones might stand side by
side.

I noted similar variations regarding a good

[Volume XI — Chapter IV]

LUTHER BURBANK

many other trees and plants of various kinds. But
I recall that the variations among the chestnuts,
and also among hickories and shell-barks, made a
very vivid impression on my mind. It seemed
strange that trees obviously of the same kind
should show such diversity as to their fruit.

When, at a later period, I began my experi-
ments in California, I recalled the variable chest-
nuts, and it occurred to me that a plant showing
such inherent tendency to vary should afford an
unusual opportunity for development — for by this
time I had come to appreciate the value of varia-
tion as the foundation for the operations of the
plant experimenter.

But I had conceived the idea also — as our
earlier studies have shown — that there would be
very great advantage in hybridizing the best
native species of plants with plants of foreign
origin. And I had the chestnuts in mind among
others when I sent to Japan and Italy and the east-
ern states for new plants with which to operate.
So the very first lot of plants that came to me from
Japan (in November, 1884), included twenty-five
nuts that I find listed in a memorandum as "mon-
ster" chestnuts. The same shipment, it may be of
interest to recall, included loquats and persim-
mons with which some interesting experiments
were made; pears, peaches, and plums of which

[96]

Six Months Old Chestnut Tree in Bearing

This is a veritable infant prodigy. Only six months ago,
its cotyledons broke the soil; and to-day it bears goodly clus-
ters of maturing fruit, as the picture shows. To cause a tree to take
on this habit of an annual plant is a remarkable
triumph of selective breeding.

LUTHER BURBANK

the reader has already heard; and climbing black-
berries and yellow and red fruited raspberries that
had a share in the development of some fruits that
presently attained commercial importance.

But perhaps there was nothing in the entire
consignment that was destined to produce seed-
lings with more interesting possibilities of devel-
opment than the 25 "monster" chestnuts. For the
hereditary factors that these nuts bore were to
have an important influence in developing new
races of chestnuts of strange habits of growth —
chestnuts dwarfed to the size of bushes, yet bear-
ing mammoth nuts, and of such precocity of habit
as sometimes to begin bearing when only six
months from the seed.

To be sure other chestnut strains were blended
with the Japanese before these anomalous results
were produced; but it is certain that the oriental
parents had a strong influence in determining
some at least of the most interesting peculiarities
of the new hybrid races.

Very Mixed Ancestry

That the antecedents of the precocious chest-
nuts may be clearly revealed, let me say at the
outset that the Japanese forms were hybridized
with the three other species as soon as they were
old enough to be mated, and that the hybrids in
turn were crossed and recrossed until the strains

[98]

Yearling Chestnut Tree in Bearing

These precocious chestnuts are complex hybrids, com-
bining the traits of European, American, and Japanese ances-
tors. Such chestnut bushes as this will perhaps take the place of the
devastated chestnut forests of our eastern states.

LUTHER BURBANK

had been blended of all the different kinds of
chestnuts that could be obtained.

These included, in addition to the Japanese
species just cited, representatives of the European
chestnut in several of its varieties — one of which
came from China — and of the native American
chestnut of the familiar type; and also the little
native species known as the Chinquapin.

It is interesting to record that the chinquapin,
with its almost insignificant nut, crossed readily
with the Japanese species, the mammoth nut of
which would seem to place it in quite another class.

But, in point of fact, there is apparently a very
close affinity between all the different chestnuts.
All of them have varied and thus perpetuated
forms that more or less bridge the gap between the
typical representatives of the different species, and,
so far as my observations go, all of them may
readily be interbred. In a word, the chestnut fur-
nishes most plastic material for the purposes of
the plant developer. Just how I have utilized that
material will appear as we proceed.

At the time when I received the chestnuts from
Japan, there were already at hand trees of the
European and American species of various sizes.
So soon as the Japanese seedlings were of sufficient
size, I grafted them on these European and Amer-
ican trees, in this way being able to stimulate

[100]

ON THE CHESTNUT

development, and to observe the progress of cions
from several hundred seedlings on the same tree.

This, of course, is precisely the method I used
with my plums and other orchard fruits. The
advantages already detailed in connection with the
orchard fruits were found to apply equally to the
chestnut. The engrafted cions were led to fruit
much earlier than they would have done on their
own roots; there was saving of space; and it was
easy to hybridize the many cions that were thus
collected on a single tree.

Of course, I was carrying forward numerous
experiments with the chestnut at the same time —
crossing each species with every other species, so
that in a single season there would be a large
number of hybrid forms of different parentage. So
when two of the hybrids were interbred, the
strains of four different species or varieties were
blended. Thus a hybrid of the second generation
might combine the ancestral strains of the Japa-
nese and European and American chestnuts and of
the little chinquapin.

Moreover I had opportunity for wide selection
among hybrids that combined these various strains
in different ways. And for the next generation, I
could combine different hybrids or inbreed a given
strain or introduce the traits of a different variety
as I might choose.

[101]

Branch of a Six Months Old Chestnut

The picture shows the way in which the chestnut burs

form in relation to the catkins. Many of the hybrid chestnuts

have the peculiar quality of putting forth blossoms at almost every

season, so that flower buds and blossoms and mature

fruit, mag be found on the same branch.

ON THE CPIESTNUT

In point of fact, all these methods were utilized,
and in addition, of course, my usual method of
rigorous selection was employed, so that I soon
had a colony of chestnuts not only of the most
complicated ancestry, but also a carefully selected
colony in which none that did not show excep-
tional traits of one kind or another had been
permitted to remain.

Precocious Traits

Of the many rather striking peculiarities of the
new hybrids, doubtless the one that attracts most
general attention is the habit of precocious bear-
ing.

From the outset my hybrids were urged to early
bearing, by the method of grafting and selection,
as already noted; and of course I saved for further
purposes of experiment only the individuals that
were the most precocious. But, even so, I was not
prepared to find my seedlings bearing large nuts
in abundance in eighteen months from the time of
planting the seed. Yet such extraordinary pre-
cocity as this was shown by many of the seedlings
in the third and subsequent generations.

Moreover, if the grafts are taken from the seed-
lings and placed on older trees, they would pro-
duce, although not so abundantly, within six
months after grafting. During the past ten years,
seedlings have quite often produced nuts, like

[103]

LUTHER BURBANK

annual plants, the first year of planting, while
growing on their own roots, and when not over
twelve to eighteen inches in height.

The value of such habits of early bearing, from
the standpoint of the plant developer, will be
obvious. Ordinarily one must expect, in dealing
with nut-bearing trees, to wait for a long term of
years between generations. In the case of the
hickory, for example, after one has planted the
nut, it cannot be expected that the seedlings will
bear flowers and thus give opportunity for a sec-
ond hybridizing for at least ten years, and no large
crop of nuts may be produced till the tree is forty
or fifty years old. So even two or three genera-
tions of the hickory compass a large part of a
century.

But with my new hybrid chestnuts, generation
may succeed generation at intervals of a single
year, just as if we were dealing with an annual
plant instead of a tree that may live for a century.
And of course to this fact very largely I owe the
rapid progress of my experiments in the develop-
ment of new varieties of chestnuts.

Not only do the mixed hybrids show this extra-
ordinary precocity, but some of them also develop
the propensity to bear perpetually. On the same
tree may be found at a given time flowers and ripe
nuts. Flowers both staminate and pistillate ap

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pear on the same tree from time to time, season
after season, and in due course the flowers are
replaced by growing nuts, so that there is a regular
succession month after month.

This habit of perpetual bearing, manifested by
a tree that ordinarily produces its flowers and in
turn its nuts at fixed seasons, is perhaps scarcely
less remarkable than the habit of early bearing.
Doubtless the two are genetrically associated.
Chestnut Seedlings

The care of the chestnut seedlings presents no
important complications.

My general plan in selecting seedlings for
further tests is the same employed in the selection
of seedling fruit trees. Prominent buds, large
leaves, thick, heavy twigs, almost invariably fore-
cast large, fine nuts. There is, however, an excep-
tion to be noted in the case of the Japanese chest-
nut, which has smaller leaves. It is necessary to
bear this in mind in dealing with seedlings that
have a Japanese strain. It is needless to say that
the capacity to select the right seedlings for preser-
vation is highly important, as an element in saving
time and expense in the practical development of
improved varieties of chestnuts.

I have already referred to the saving of time
that may be accomplished through grafting the
chestnut seedlings instead of waiting for them to

[106]

<% .-. f

A ''Low Head" Chestnut Hybrid

This hybrid chestnut is six years old, but has been
headed in such a way that it forms a low bush. Com-
pare with the tree of different type shown in the succeeding picture.

LUTHER BURBANK

develop on their own roots. Unlike most other
trees, the chestnut should not be grafted until just
before the bark begins to slip in the spring. If
grafted much earlier it is necessary to protect the
grafts by tying a paper sack over them until they
start growth to prevent evaporation; but in every
case it is better to wait till shortly before the bark
begins to slip. This is unlike the cherry, which
must be grafted very early or success is extremely
doubtful.

When grafting is performed after the bark
begins to slip, it is necessary to tie down the bark
against the graft with a string to keep it in place,
otherwise it rolls away from the graft and union
does not take place. If grafting is done at the right
time and with reasonable care, it is usually
successful.

In the main, very little attention has been paid
to the chestnut by cultivators of nuts. Until very
recently, such chestnuts as have appeared in the
market have been gathered from wild trees, or,
imported from Europe. Recently, however, the
possibility of cultivating the chestnut has gained
a good deal of attention and in a certain number
of cases orchards have been started. I have intro-
duced three different varieties of hybrid chestnuts,
one of them known as the Hale, another as the
Coe, and the third as the McFarland, and these

[108]

'High Head" Chestnut

This tree, like the one shown in the preceding picture, is

six years old. Like the other, it is a complex hybrid, but it

has been allowed to take on an upright growth, similar to that of the

common American chestnut. The complex chestnut hybrids

show the widest range of variation as to form

and size and manner of growth.

LUTHER BURBANK

have been grafted on ordinary chestnut stocks to
form the basis of many chestnut orchards of the
southern states.

In some cases the roots of the chinquapin have
been used as the foundation for grafting, in regions
where the ordinary chestnut does not occur. Chest-
nut orchards have also been started by planting the
seed. Reasonable success attends this method, but
of course it lacks the certainty of grafting. Now-a-
days no one attempts to start an orchard except
by grafting.

Unfortunately there has developed within very
recent years a disease that attacks the chestnut
tree and invariably destroys it. The disease at
first appeared in the neighborhood of New York
City about the year 1904, and it has spread in all
directions each year reaching out a little farther,
until in 1914 there were very few chestnut trees
unscathed within fifty or sixty miles of the original
center of contagion.

The cause of the disease is a fungus that is
perpetuated by minute spores that are presumably
carried through the air and that, when they find
lodgment, develop in such a way as to destroy the
cambium layer of the bark, presently causing the
death of the tree. The small twigs of a single
branch will often first show the influence of the
fungus and the leaves may die and become brown

[110]

Chinquapins and Chestnuts

The chinquapin is a species of chestnut bearing very small
nuts, which have, however, the typical chestnut form and qual-
ity. The picture, showing chinquapins at the top and chestnuts be-
low, illustrates both the similarity in form and the contrast
in size. The strains of the chinquapin have been
combined with those of the other chestnuts
in Mr. Burbank's complex hybrids.

LUTHER BURBANK

and shriveled on one or two large limbs of the
tree when no other part of it is affected. But in
the ensuing season the disease is sure to spread,
and the tree seldom survives beyond the third year.

As yet no way of combatting the pest has been
suggested, except the heroic measure of cutting
down trees immediately they are attacked, and
burning every portion of their bark. In this way
it is hoped to limit somewhat the spread of the
disease but it is by no means sure that the method
will be effective. There appears to be danger that
the pest will spread until it has decimated the
ranks of the chestnut throughout the eastern
United States; and of course there is no certainty
that it may not find its way to the Pacific Coast,
although the lack of chestnut trees in the desert
and plateau regions of the middle west may serve
as a barrier.

The precise origin of the fungus that causes the
disease was not known until the summer of 1913,
when it was discovered by Mr. Frank N. Meyer, of
the United States Department of Agriculture, that
the fungus (which bears the name Endothia para-
sitica) is indigenous to China. The Oriental chest-
nut trees have become practically immune to it,
however, and it does not destroy them, but merely
blemishes their bark here and there with canker
spots. No one knows just how the disease found

[112]

ON THE CHESTNUT

its way to the United States, but it presumably
came on lumber brought from the Orient.

The appearance of this pest came as a very dis-
couraging factor just at a time when interest in
the chestnut as a commercial proposition was
being thoroughly aroused. Government bulletins
had called attention to the value of its nut and its
possibility as a paying crop.

But, of course, all expectations were nullified in
the regions where the ravages of the chestnut fun-
gus are felt.

Fortunately, it appears that some of the hybrid
races that bear the Oriental strain are immune to
the disease. Observations as to this have been
made very recently by Dr. Robert T. Morris, of
New York. Reports show that hybrids between
the Japanese chestnut and the American Chinqua-
pin are peculiarly resistant. The chinquapin itself
is at least partially immune to the disease, but of
course this plant bears a nut that is too small to
have commercial value. The hybrids, however,
in some cases are said to retain the good qualities
of the chestnut tree combined with the capacity to
bear large nuts acquired from their Oriental
ancestor.

It is obvious, then, that here is another case in
which the introduction of new blood from the
Orient may be of inestimable value. The loss of

[113]

A Typical Cluster

This typical cluster of hybrid chestnuts, in the

formative stage, suggests the prolific bearing of the tree.

What the hybrids lack in size, they appear to make up in productivity.

ON THE CHESTNUT

our native chestnuts is indeed a calamity, but it is
a calamity that is not irreparable. We may have
full assurance that new chestnut groves will spring
up in the wake of the pest.

It is obvious that the quick growing chestnut
offers great advantages for such reforestration.
The probability that these will prove immune to
the pest gives them added attractiveness. If, how-
ever, the existing varieties should prove not to be
immune, it will be necessary to develop resistant
varieties. For it is obvious that the cultivation of
the chestnut will not be abandoned merely because
it has met with an unexpected setback.

It has already been pointed out that the chest-
nut has exceptional food value on account of its
high percentage of starchy matter. It therefore
occupies a place in the dietary that is not held by
any other nut. So there is an exceptional incentive
to reintroduce the trees in devastated regions.
The Chestnut Orchard

Possibly the coming of the chestnut plague,
even though it has resulted directly in the destruc-
tion of the entire chestnut groves throughout wide
regions, may be a blessing in disguise, as it may
make it necessary to bring the chestnut under
cultivation in order to preserve the nut at all,
whereas in the past it has grown so abundantly in
the wild that little attention has been paid to it.

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ON THE CHESTNUT

Accounts of the destruction of the trees have
doubtless brought the chestnut to the attention of
many people who hitherto have never given it a
thought. The value of the chestnut as an orna-
mental tree and its possibilities as a nut producer
will perhaps be more fully appreciated than they
otherwise would be on the familiar principle that
blessings brighten as they take their flight. And
it may chance that the tree will be placed under
cultivation so generally as to be more abundant
twenty-five or thirty years from now in the de-
vastated regions than it would have been if the
chestnut blight had not appeared.

In any event it seems now at least as desirable
as ever before to urge the value of this tree both
for ornamental purposes and as a producer of
commercial nuts, and the rules for the develop-
ment of chestnut orchards that have been given
by the Department of Agriculture may be reviewed
to advantage.

Even if people living in the infected district are
slow to take up the cultivation of the chestnut, the
orchardists of other regions may advantageously
do so. For I repeat that it is not supposable that
the coming of a fungoid pest will be permitted to
exterminate one of our most valuable native trees.

In developing a commercial chestnut orchard
it is obviously desirable to graft with the improved

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ON THE CHESTNUT

varieties. Quite aside from the matter of produc-
ing trees that are immune to the fungus pest, the
orchard may be made far more productive if
grafted with foreign stock than if the native
species were used. And of course my new hybrid
varieties offer attractions that excel those of any
other variety of chestnut.

Some of my seedlings, for example, produce
nuts two inches in diameter, each weighing an
ounce or more; and these are borne in clusters of
from six to nine nuts to the burr. It is notable,
however, that the excessively large nuts are usually
lacking in flavor; although the reasonably large
ones are of the best quality.

These hybrid varieties graft readily on the
native stock. They may be counted on to bear
abundantly in their second season. It may be
well, however, to pick off the burs as soon as
formed during the first year or two, in order that
the energies of the tree may be given over to the
production of branches.

Even where the blight has destroyed the chest-
nut, the sprouts that spring up everywhere about
the stumps of the trees may be grafted and trees
of more satisfactory shape than the old ones and
far more productive may thus be developed in the
course of a very few years.

Where the chestnut orchard is developed from

[119]

LUTHER BURBANK

the seed or by transplanting seedlings, it is recom-
mended that it should be located on a well drained
gravelly soil. The trees thrive well on rocky hill-
sides, and even on rather poor sand, but observa-
tion has shown that they are somewhat uncertain
of growth on stiff clay soils in the east, although
Italian chestnuts in California are said to thrive
on heavy clays. In general, the experts consider it
more important to have a thoroughly drained soil
than soil of a particular character.

The authors of the Government Bulletin that
has urged the merits of the chestnut as a commer-
cial crop show that the chinquapin chestnuts are
practically free from the blights that have hitherto
menaced the American species.

It will be recalled that my new varieties were
developed on the foundation of stocks imported
from Japan. It will also be understood, as a mat-
ter of course, that my selections with this tree as
with all other plants have been made always with
an eye to the exclusion of any races that showed
susceptibility to fungus pests of any kind.

As an illustration of the care with which these
selections were made, in the development of the
perfected varieties, I may note that in various
instances only three or four seedlings were selected
out of a company of ten thousand. I may add that
orchards made by grafting cions of these im-

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LUTHER BURBANK

proved hybrid chestnuts on ordinary American
stock have proved enormously productive.

It has been estimated that rocky and otherwise
useless hillsides may be made productive, where
practically nothing else could be grown that would
be of special value.

Improvements to be Made

In continuing my experiments in developing
the chestnut, I have endeavored to effect wider
hybridizations. In particular I wish to cross the
hybrid chestnut with the evergreen golden chest-
nut (Castanopsis chrysophylls) of California, but
the wild trees of this species are so distant from
my grounds that I have not found it feasible to
gather their pollen, and the ones I have under
cultivation, although fifteen years of age, have not
yet blossomed.

This golden chestnut is a very remarkable
species. On the heights of the Sierra Nevada
mountains it grows as a shrub only four or five
feet tall, much branched. These shrubs produce
nuts quite abundantly. Along the coast the same
tree grows to a height of 150 feet, with an immense
trunk. One can scarcely believe that the little bush
and the gigantic tree are of the same species.

In point of fact there is a considerable differ-
ence in the constitution of the two varieties, the
giant from along the coast being rather tender,

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while the bush-like mountain form is very hardy.

Being an unusually ornamental evergreen the
mountain variety should be extensively planted
in cold climates.

I am inclined to believe that the golden ever-
green chestnut and the chestnut oak could be com-
bined by crossing. If so, remarkable trees could
be produced.

As yet, however, I have not been able to attempt
this hybridization, nor, indeed, have I as yet
hybridized the golden chestnut with the ordinary
chestnut, for the reason above stated.

I have made tentative efforts, however, to cross
my early bearing hybrid chestnuts with the Cali-
fornia tanbark or chestnut oak, Quercus densi-
florus.

Notwithstanding the wide difference between
the species, numerous nuts were produced and it
seems probable that these were hybrids. As to
this, however, I cannot be certain until the seed-
lings have come to maturity.

The object of such wider hybridizing is, in
particular, merely to test the possibilities of cross-
ing a plant that shows a high degree of inherent
flexibility. But it is also desirable for practical
reasons to accentuate the variability and to carry
forward further series of experiments in selective
breeding.

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There is a great difference among the different
chestnuts as to the amount of their sugar content.
In some species the starch is so little transformed
that the nuts are scarcely edible unless cooked. In
others there is an abundant sugar content the nuts
being sweet and palatable. Of course I have had
this matter in mind in developing my hybrid vari-
eties. But there is still opportunity for improve-
ment.

It is also desirable to reduce the amount of
tannin contained in some of the chinquapin
varieties.

Some of the chinquapin varieties also have the
habit of holding the leaves during the winter, giv-
ing the trees a very untidy appearance. Seedlings
that show this tendency should be avoided in
making selection.

Points in Selection

Of course it is elementary to say that the nuts
should be selected for dark, rich, glossy brown
color, for tenderness of flesh, and for productive-
ness. Of my three introduced varieties, all were
early and abundant bearers, but one was particu-
larly notable for its earliness, and another for its
combination of good qualities.

Doubtless the feature that is next in line of
improvement in the development of the chestnut
is the bur itself, which should be made spineless.

[126]

Bur and Catkin

It always seems matter for surprise that the round bars

of the chestnut should grow in catkins that seemed destined to

produce fruit-clusters of a quite different type. Here is a picture that

emphasizes the contrast, as it shoivs a well developed bur in

connection with the remains of the catkin. As the stam-

inate and pistillate flowers of the chestnut are

borne in different clusters, cross polleniza-

tion is very readily effected.

LUTHER BURBANK

In the wild state, the chestnut needs a spiny bur
to protect it from squirrels and birds. It has de-
veloped this protective covering through natural
selection, just as the walnut has developed its thick
coat filled with bitter and astringent juices. But
the cultivated chestnut does not require the pro-
tective spines, and it will be obviously advantage-
ous from the standpoint of the cultivator to have
these removed.

I have for some years been working on the
hybrid chestnuts with this in mind. I now have
one variety that is relatively spineless, its burs not
having more than one spicule where the ordi-
nary chestnut bur has ten. There is every reason
to expect that in a few generations more I shall
develop a chestnut that has a bur as smooth as
that of the walnut. The partially spineless variety
that I have developed has nuts that are not as
large or as good in quality as could be desired. But
for the moment I am selecting it solely with refer-
ence to the removal of spines; being confident that
once this is attained there will be no difficulty in
breeding the good qualities of the hybrid nut into
the combination.

The new partially spineless variety has been
developed merely by selection from a hybrid seed-
ling that produced nuts showing a tendency to
have fewer spines than ordinarily. Of course the

[128]

ON THE CHESTNUT

tendency to vary in this regard was accentuated by
hybridization just as were other tendencies. Or,
stated otherwise and a little more technically, the
hybridization has made possible the segregation of
hereditary characteristics, bringing to the surface
factors for spinelessness that no doubt have been
transmitted as recessive traits for a very large
number of generations.

Doubtless there was a time when the chestnut
did not have a spiny bur.

So my spineless variety, when perfected, will
represent a remote reversion, or the bringing to
the surface of a tendency that has long been sub-
merged.

No doubt difficulties will be involved in perfect-
ing the race of chestnuts with smooth burs similar
to those that attended the development of the
thornless blackberry and the spineless cactus. But
there is reason to expect that the same measure of
success will be attained with the chestnut that was
attained with the other spine bearers.

A nut that combines all the good qualities of
my hybrid early bearing chestnuts and in addition
is born in a spineless bur would have a combina-
tion of qualities that should appeal to the orchard-
ist, and doubtless will do so when the idea that
nuts may form valuable commercial crops gains
wider vogue.

[129]

A Hickory Tree

The hickories are native American trees celebrated for the

quality of their wood as well as for their nuts. In some parts of

New England the hickory is colloquially known as the "white walnut.

The Hickory Nut— And
Other Nuts

Improvements Which Have Been Wrought
And Some Suggestions

THERE is perhaps no other wild plant pro-
ducing a really delicious food product that
has been so totally neglected by the culti-
vator as the shagbark or shellbark hickory tree.
The better varieties of hickory-nuts always find
a ready sale in the market, and are highly prized
by the housekeeper. But such nuts as find their
way to the market are almost without exception
the product of wild trees, gathered usually by some
wandering boy, and often regarded as the property
of whoever can secure them, regardless of the
ownership of the land on which the tree grows.

Even the new interest in nuts as food products
and as orchard crops that has been developed in
our own generation, has not as yet included the
hickory, or at least has not sufficed to bring the
hickory tree from the woods and give it a place
within the territory of the orchardist.

[Volume XI — Chapter V]

LUTHER BURBANK

The reason for this, doubtless, is that the
hickory is a tree of very slow growth, and that it is
also exceedingly difficult to propagate by budding
or grafting, or any other process except from the
seed.

The prospect of improving the product of a
tree that does not bear until it is ten or fifteen years
old, and that resists all efforts to force it to early
bearing, is not alluring, considering the short span
of human life. Yet we can scarcely doubt that the
hickory nut will presently be brought within the
ken of the plant experimenter, and that there will
ultimately be developed nuts of very choice varie-
ties, comparable in size, probably, to the English
walnut, and having a quality that will place them
at least on a par with any other nut now grown in
the temperate zones.

Even in the wild state, the best of shellbark
hickories bear nuts of unchallenged quality. It is
a matter of course that these nuts can be improved
by cultivation and selective breeding.

Material for such selective breeding is fur-
nished abundantly by the wide variation of hick-
ories in the wild state. I had observed this varia-
tion in my boyhood days, just as I had noted the
variation in the chestnuts. The shagbark hickory,
doubtless the best of the tribe, was quite abundant
along the banks of the Nashua River near my

[132]

ON THE HICKORY NUT

home, and I early learned to distinguish the great
difference in the products of the trees, all of which,
of course, were natural seedlings.

Among hundreds of trees there would be
scarcely two that bore nuts of precisely the same
appearance and quality.

Some of these hickory nuts were long and
slender, with prominent ridges; some were short
and compact and smooth in contour; some were
very flat and others were nearly globular. The
shell varied correspondingly in thickness, and the
meat varied greatly in whiteness and in flavor.

As a boy I knew very well which trees to seek
in the fall in order to secure nuts that were plump
and thin-shelled, with sweet and delicious meats.
It was only after the crop of these trees had been
gathered that inferior ones gained attention.

I knew very well, also, that different trees
varied greatly in productiveness, some bearing
nuts so abundantly each year that the ground was
literally covered when the nuts fell. Others pro-
duced nuts very sparingly.

The trees that thus varied as to their fruit,
varied also in form, in size, and in rapidity of
growth. In a word, the wild hickories represented
numerous varieties that a boy could differentiate,
whether or not a botanist might choose to classify
them as members of the same species.

[133]

LUTHER BURBANK

All these varied members of the shagbark tribe
bore nuts that had an unmistakable individuality
of flavor that distinguished them from any other
nuts. Much as they varied in size and degrees of
excellence, all of them were hickory nuts, and
could be mistaken for nothing else. There were,
however, other hickory trees growing in equal
abundance on my father's place, though they dif-
fered essentially in appearance from the shagbark
nuts, that produced nuts of a far less interesting
character.

Hickories of this kind were locally called pig-
nuts. They are classified by the botanist as
Hicoria glabra.

The trees of this species are more upright and
symmetrical, and of much more rapid growth than
the shagbark. The nut has a thin husk-like shell,
but the meat is difficult to remove, and is so ill-
flavored that it is little prized by any one. Indeed,
the nuts are usually not gathered at all if shagbark
hickories of any quality can be obtained.

Nevertheless, there was great diversity among
the pig-nuts no less than among the hickories of
the better species. So with these also there is
doubtless opportunity for improvement through
selective breeding, although up to the present time
no comprehensive experiments in this direction
have been made.

[134]

Hickory Nuts

There is marked variation in the size, form, and quality

of the nuts of different hickory trees, even when growing in the

same neighborhood. Thus their is good opportunity for selective

breeding, but unfortunately the hickory is of such slow growth

that few experimenters have the courage to undertake its

development. The hickory does not ordinarily

bear nuts until it is ten or twelve years old.

LUTHER BURBANK

I have now little doubt that some of the variant
hickories that I knew as a boy were hybrids.

The two species of hickory are closely related,
and I have reason to believe hybridize not infre-
quently in the wild state. I have received speci-
mens of hickory nuts from different parts of the
United States that I feel certain were natural
hybrids. And I entertain no doubt that such
hybridization occurs not infrequently.

It is probable that when the attempt is syste-
matically made to develop the hickory nut the
method of hybridizing the two species will be
employed to give still wider variation and to
facilitate a wider selection.

Some Enormous Hickories

There is a variety of the hickory nut that grows
in the valleys of the Mississippi and the Ohio that
is of relatively enormous size. The shell of this
variety, however, is thick, and the meat is not
generally as fine in flavor as that of the eastern
shellbark hickory. But the size of this wild variety
gives assurance that under cultivation and selec-
tion the nut may be made to take on proportions
that will be very attractive. Doubtless the com-
paratively small size of the wild hickory nut has
led to its neglect, although we must recall that the
walnut and the butternut have also been neglected,
notwithstanding their much larger size.

[136]

ON THE HICKORY NUT

The chief reason why these nuts have been
overlooked, doubtless, is that the idea of making
nuts a cultivated crop, comparable to orchard
fruits, has only recently been conceived in America
— or at all events has only recently been given
general recognition.

It is not improbable that it may be found
feasible to hybridize the hickory with the black
walnut or the butternut. These trees, to be sure,
do not belong to the same genus, but they are not
very distantly related, and we have seen that
generic bounds do not necessarily constitute
impassable barriers.

Could hybridization be effected between the
hickory and either the walnut or the butternut, the
product should be a nut of very great value.

It would be necessary, of course, to breed
selectively, doubtless for a number of generations,
to secure size and quality, and in particular to
develop a race of thin-shelled nuts. But that all
this may be accomplished cannot greatly be in
doubt. In any event, the experiment is well worth
making.

There is reason to expect that the next three
or four generations will see somewhat the same
rapid progress in the art of developing the nut-
bearing trees that has been witnessed in the past
three or four in the development of orchard fruits.

[137]

LUTHER BURBANK

And certainly the hickory nut, walnut and butter-
nut constitute better native material than the wild
plums, for example, with the aid of which some
of the finest varieties of cultivated plums have
been developed within the most recent years.

And, indeed, it must not be forgotten that the
work of developing our native nuts has already
passed the experimental stage with regard to at
least one species. This is the nearest relative of
the hickory, a member indeed of the same genus,
which is familiar as the pecan.

This nut grows only in the southern parts of
the United States, being far less hardy than the
other hickories. But what it lacks in hardiness it
makes up in quality, and it is pretty generally
regarded as the best nut that is grown in temperate
climates, not even excepting the English walnut.

The relationship between the northern hick-
ories and the pecan is attested by the fact that in
the regions where the two tribes intermingle, they
hybridize freely.

I have received specimens of the nuts that were
undoubtedly hybrids between the shagbark hick-
ory and the pecan, and these included two or three
varieties that are among the finest nuts that I have
ever seen.

The seedlings that grew from them included
two trees that gave great promise. Unfortunately

[138]

A Butternut Tree

The butternut is an indigenous tree, closely related to

the black walnut. As a timber tree, it is inferior to the walnut,

but it bears a nut of very exceptional quality. It is to be hoped that

someone ivill make the experiment of hybridizing

the butternut and the walnut.

LUTHER BURBANK

the gophers destroyed them both. So the experi-
ments I had contemplated in connection with them
were not carried out. But I am confident that
great improvements in the pecan will result from
hybridizing this nut with the shagbark hickory.
The Cultivation of the Pecan

Even in its existing varieties, however, the
pecan nut has very attractive qualities; and it has
the distinction of being the only native nut that
has hitherto been placed under cultivation on an
extensive scale and has attained commercial
importance.

We have already referred to the economic
importance of this nut in an earlier chapter, and
mention was there made of the fact that all the
pecans now under cultivation are directly derived
from a few wild varieties that have been propa-
gated by budding and grafting. It is only in recent
years that a method of grafting this nut success-
fully has been developed, and as yet little or noth-
ing has been done toward improving the wild
varieties.

The fact that the nut in its wild state has such
attractive qualities gives full assurance that under
cultivation and development it will prove of even
greater value.

In selecting the best wild varieties for cultiva-
tion, attention has been paid to the matter of early

[140]

ON THE HICKORY NUT

bearing, and in particular to persistent bearing.
So the orchards that have recently been started
are stocked with trees that may be expected to
bear crops of nuts in about seven or eight years,
and that may be depended on to produce a crop
each year with reasonable certainty. But as to
both time of bearing and regularity and abundance
of production, there is still opportunity for much
improvement.

Doubtless improved varieties may be secured
through mere selection by raising seedlings from
the nuts grown on trees that were especially good
bearers. But it is probable, also, that the full pos-
sibility of the pecan will not be realized until ex-
tensive series of hybridizing experiments have
been carried out.

I have spoken of the natural hybrids between
the pecan and the shagbark hickory. Hitherto, no
extensive experiments in hybridizing these species
have been carried out, although it is possible that
some of the wild varieties of pecans that have been
brought into the orchard were natural hybrids.

It is to be hoped that experiments along this
line will be taken up in the near future, but, of
course, many years will be required before notable
results can be attained.

It is desirable, also, to attempt hybridizing the
pecan with the butternut and walnut, and with the

[141]

I ■

A Pecan Tree

The pecan is closely related to the hickory, but is a much
less hardy tree, being confined to our southern states. It some-
times hybridizes with the hickory in the wild state, and it is possible
that new and hardy varieties of nuts might be produced by
selection among the progeny of such a cross. The pecan
is rapidly assuming importance as a commercial nut,

ON THE HICKORY NUT

English walnut and the Japanese walnut. If
hybridization could be effected, it may be expected
that trees of rapid growth, similar to my hybrid
walnuts, will be produced. Not unlikely some
varieties that tend to produce nuts at a very early
age, like my hybrid chestnuts, may also appear as
the result of such combinations. And in any event
it may confidently be expected that new varieties
will give opportunity for wide selection, and for
relatively rapid improvement in the qualities of
the nuts themselves.

We have learned that the pre-eminent qualities
of our various cultivated fruits have largely been
given them by hybridization.

The contrast between the tiny beech plum, for
example, and its gigantic descendant a few gen-
erations removed, offers an object lesson in the
possibilities of fruit development by hybridizing
and selection. And, for that matter, each and
every one of our improved varieties of orchard
fruits teaches the same lesson, even though the
wild progenitor is not at hand for comparison.

So there is every reason to expect that the wild
pecan will similarly respond to the efforts of the
plant developer, and that its descendants, a few
generations removed, will take on qualities that
even the most sanguine experimenter of to-day
would scarcely dare to predict.

[143]

LUTHER BURBANK

One improvement that might probably be
secured without great difficulty is the introduction
of the quality of hardiness, so that the pecan might
be cultivated farther to the north. At present the
pecan does not produce profitably as a rule, even
in the coast counties of California, as the nights are
too cool, thus making the season too short for the
pecan to ripen its fruit. About Vacaville they
thrive much better, and the Sacramento and San
Joaquin Valleys, where the nights are very warm,
there is as good prospect of growing the pecan
profitably as anywhere else in the world. But in
the main the cultivation of this nut has hitherto
been restricted to the region of the Gulf of Mexico.
It is obviously desirable that so valuable a nut
should be adapted to growth in wider territories.

The fact that the pecan will hybridize with the
hardy hickory obviously points the way to th'~
method through which this end may be attained.

The peculiarity of the hickory and pecan that
is associated with their long life and slow growth,
is the fact that during their first year the seedlings
make perhaps 99 per cent, of their growth under
ground. They produce enormous roots before they
make any appreciable growth above ground.

It is nothing unusual to find pecan seedlings
an inch high with roots from four to six feet in
length, and an inch in diameter at the widest part.

[144]

The Hazelnut

The hazelnut grows wild in many regions of our eastern
and central states, but it is almost never seen under cultivation.
There are several varieties, and they would probably repay experi-
ments in selective breeding. There is no reason why the
hazelnut should not have commercial value
if properly cultivated.

LUTHER BURBANK

Such a root system prepares the tree for the
strong growth that characterizes it later; but a
seedling that makes only a few inches of growth
in the first season is a rather discouraging plant
from the standpoint of the cultivator. Doubtless
the pecan may be induced to change its habit in
this regard by hybridizing. The example of the
hybrid walnuts may be cited as showing that a
tree that is ordinarily slow of growth may be made
to take on the habit of very rapid growth without
relinquishing any of its other characteristics of
hardiness and the production of valuable timber.

The case of the Royal walnut shows also that
the tree that thus becomes a rapid grower may
also have the habit of enormous productivity.

If the pecan could similarly be stimulated to
increased rapidity of growth, and to a proportion-
ate capacity for nut bearing, this tree would be a
fortune-maker for the orchardist. And there is no
obvious reason why the pecan should not have the
same possibilities of development that have been
demonstrated to be part of the endowment of its
not very distant relative, the walnut.
Filberts and Hazelnuts

There is yet another native American nut as
hardy and as widespread as the hickory, that has
been even more persistently neglected. This is the
familiar hazelnut.

[146]

ON THE HICKORY NUT

There are two familiar types of hazelnut that
often grow in the same region, and that resemble
each other so closely that the boys who gather the
nuts commonly do not discriminate between them.
One of these grows in husks with a long beak,
while the other has an incurved husk that in some
cases does not fully cover the nuts. There are
sundry varieties of the two species that may some-
times be found growing in the same patch.

The fact of such variation in the wild species
is of course important from the standpoint of the
would-be plant developer. We have learned from
frequent repetition that where there is variation
there is opportunity for selection and improve-
ment.

The hazelnut has a European relative that is as
familiar in America as the filbert. This is merely
a larger hazelnut, the qualities of the two nuts
both as to form and flavor being such as to leave
no question of their relationship. But for some
reason the European nut appears not to thrive in
this country. At all events it has never been culti-
vated here on a commercial scale.

But for that matter the hazelnut has never been
cultivated on a scale commercial or otherwise,
unless in the most exceptional instances when it
has been brought into the garden by some one
rather as a curiosity than for any commercial pur-

[147]

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ON THE HICKORY NUT

pose. Yet the nut is a really valuable one, and
certainly it is one that would repay cultivation and
development.

Attempts have been made to grow the Euro-
pean filbert in Sonoma County, California, both
from seed and from division, but in all cases these
attempts have failed. The purple-leaved hazelnut
grows and thrives here in California as it does
almost everywhere else in the United States. The
species known as Corylus rostrata grows wild
rather abundantly in certain sections, but so far
as I have observed, it is a shy bearer.

There is no obvious reason why the European
filbert should not be cultivated in this country if a
study is made of its needs as to soil and climate.
Also, there is no seeming reason why it should not
be hybridized with the American hazelnut. The
result of such hybridizing, if we may draw infer-
ences from analogy, would be the production of a
race of hazel-filberts of greatly increased size, and
of improved quality.

There is a so-called filbert, or Chilean hazelnut,
that grows in South America. This plant bears a
nut similar to the filbert, but much larger in size
and of far better quality. It is difficult, however,
to get a start in the cultivation of this plant, as its
seeds when brought to this country ordinarily do
not germinate. I have at last succeeded, however,

[149]

LUTHER BURBANK

in producing several young trees. The nut is four
times as large as the hazel nut. This is a beautiful
tree, and should prove of great value. In its own
country the plant is very highly prized, selling for
a large sum when only a few inches high.

The European filbert grows readily from the
seed, but does not by any means come true. In-
deed, it proves exceedingly variable. But this, of
course, from the standpoint of the plant developer
could not be regarded as a fault. If through se-
lective breeding a variety could be produced that
would bear regularly and abundantly, and in par-
ticular if the size of the nuts was increased, this
would be one of the most important of all nuts.
As yet, however, a variety that is adapted to
growth in this country has not been produced.

So there is abundant opportunity for work on
the part of the plant experimenter.

With the American hazel and the European
filbert for material — whether or not further aid
may be expected from the Chilean species — there
is opportunity to produce a nut that will amply
repay almost any experimenter for the time and
labor that may be spent upon it.

Some Foreign Possibilities

A nut that has come to be fairly well known in
the market in recent years, but which has hitherto
scarcely been grown in this country, is the

[150]

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Pistachio. The tree on which this nut grows is a
member of the sumac family. The nuts are small,
but on the best trees are produced in profusion.

In recent years the Department of Agriculture
of the United States Government has imported a
great number of plants and seeds of the pistachio,
which are now being grown experimentally, and
which, it is hoped, will form the basis of an ex-
tensive culture of this nut. The experiment has
not as yet progressed far enough to make predic-
tion possible as to the results. My own experience
with the nut is limited to the growing of a single
plant about twenty-five years ago, which, after I
had cultivated it for a dozen years was found not
to be a fruiting variety, and so was destroyed.

An Australian tree-shrub or small tree, called
the Macadamia ternifolia, has been introduced in
California in recent years, and is regarded as a
valuable acquisition. The tree is ornamental, and
it bears a fruit that is regarded as of value. At the
center of the fruit is a round, delicious nut, much
larger than the ordinary filbert, indeed, sometimes
almost equaling a small English walnut, that is
fully equal in flavor to the best filbert or almond.

The Macadamia has proved hardy in this
vicinity, but requires a well-drained soil. A wet
winter is very destructive to the trees, unless they
are on dry, well-drained land.

[152]

ON THE HICKORY NUT

There are several species of Macadamia, the
one that I have raised most extensively being
known as Macadamia ternifolia. This is a hand-
some evergreen, the leaves of which resemble
those of the magnolia, but are thinner and rougher.
The nuts are often an inch in diameter, with
rather thin shells, and large, round, delicious
meats. Further tests will be necessary before the
climatic limitations of the Macadamia are fully
established. But in regions where it can be grown,
it must prove a nut of very great value.

— The prospect of improving
the product of a tree that does
not hear until it is ten or fif-
teen years old, is not alluring,
considering the short span of
the human life; yet we can
scarcely doubt that even the
hickory nut will presently be
brought into the dominion
of the plant experimenter.

A Maple Tree

Maples of various species are among the most attractive
of our indigenous trees. They are ornamental in our parks and
dooryards, some of them furnish timber of very high grade, and one
of them furnishes a sap that is transformed into the most de-
lectable of sugars. The California species here shown
is chiefly prized for its ornamental qualities

0* *4&

*tf^°°

On Growing Trees
for Lumber

Ideas On Profitable Re-Forestration

A GOOD many years ago I had a talk with an
official connected with the Department of
Forestry, at Washington, in which I sug-
gested that the problems of his department could
best be met by the development of new types of
forest trees.

The official regarded the suggestion as
grotesque. In common with nearly everyone else
at that time he looked upon the tree as a fixed
product of nature, quite beyond the possibilities of
any change that man could direct.

That was the time when Darwinism, although
it had pretty fully established itself in the scien-
tific world, was still on trial in the minds of the
people in general. And even those who accepted
the general truth of the Darwinian doctrine of
evolution for the most part did not realize that
evolution is a process that is going on about us

[Volume XI — Chapter VI]

LUTHER BURBANK

to-day along the same lines that have character-
ized it in the past.

To accept the doctrine of evolution at all re-
quired the overturning of the most fundamental
ideas. After the conception had been grasped that
in the past there had been eras of change and
development, it was a long time before even the
most imaginative scientist fully grasped the notion
that our age also is a time of change and transi-
tion, and that the metamorphoses of plants and
animals through which new forms have evolved
in the past are being duplicated under our eyes
in our own time.

And in particular, as regards so massive and
seemingly stable a structure as the tree, was it
peculiarly difficult for botanists to conceive of
flexibility and propensity to change, or to evolve,
in the present time.

It is true that no very keen eye was required
to observe that trees differ among themselves
within the same species, but it is also true that
these divergencies always fall within certain lim-
its and that on the whole they may be regarded as
insignificant when weighed in the balance against
numberless characteristics in regard to which the
trees of a species seem practically identical.

Take, for example, all the individuals that one
could observe of, let us say, the common shagbark

[156]

Two Cypresses

Here the Australian cypress is shown growing side by side
with an unidentified variety. Note the very striking contrast in
the foliage of the two species; but note also how the two show rela-
tionship in their tendency to towering, slender growth.
The central stalk of each tree is as straight
as the traditional arrow.

LUTHER BURBANK

hickory, the variations of which were referred to
in the preceding chapter. Attention was called to
the fact that the hickories that I used to observe
as a boy in the neighborhood of my New England
home differed a good deal in size and form, and
that the nuts that they bore were sometimes oval,
sometimes rounded in form, sometimes rough,
sometimes smooth, sometimes thick, and some-
times thin of shell, and equally diversified as to
the quality of their meat. But of course I should
be foremost to admit that all these diversities were
in the aggregate of minor significance in compari-
son with the characteristics that even the most
divergent of the hickories had in common each
with all the rest. All of them were trees that
attained a fair size as trees go.

All have roots and trunks and branches of the
same general form and aspect — as much alike, for
example, as the bodies and arms and legs of
human beings.

All of them had leaves that could at once be
distinguished as being leaves of the hickory and
of no other tree.

All had bark with the same characteristic whit-
ish color and the same propensity to scale off in
layers; and although the bark of some was much
rougher than that of others, any fragment of bark
of any hickory tree could readily enough be dis-

[158]

ON TIMBER TREES

tinguished as characteristic of the species, and as
not by any chance having grown on any other
kind of tree..

Then, too, if the hickory tree were felled and
cut into fire wood, the texture and fiber of the
wood itself enabled anyone who glanced at it to
pronounce it hickory as definitely and with as
much certitude as if he had seen the tree while
living and in full leaf. No other wood had quite
the same whiteness, quite the same strength and
elasticity of fiber.

The Indians had learned this in the old days,
and had used the hickory of a preference always
in making their bows.

We boys, in our barbaric age, followed the
Indians 'example. We knew that a bow of hickory
had shooting qualities that no other bow could
hope to match.

All in all, then, the hickory, despite the triviali-
ties of variation which are mentioned in the pre-
ceding chapter, stands apart when we come to
scrutinize it comprehensively, as a tree differing
from all others and obviously entitled to stand as
a unified and differentiated species.

And what is true of the hickory is no less true
of each and every species of tree in our forest.
Each walnut and oak and beech and birch and
pine and linden and locust has a thousand points

[159]

A Hybrid Evergreen

This is a cross between the cypress and the juniper. Mr.

Burbank notes that our evergreen trees frequently hybridize in

a state of nature. This is not strange, considering that the conifers

send out their pollen in clouds to be scattered at

random by the winds.

ON TIMBER TREES

of unison with every other member of its own
species, could we analyze its characteristics in
detail, for every conspicuous point of divergence.
If we consider minutiae of detail as to size and
exact form of leaf and all the rest, no two individ-
uals are identical. But if, on the other hand, we
take the broad view, it is clear that each recognized
species stands out in a place apart, grouped with
all the other members of its own kind, and some-
what isolated from all other species.

Such being the obvious fact, it was perhaps not
strange that the botanists and foresters of twenty-
five years ago looked almost with suspicion on
anyone who suggested that the different species of
forest trees might be interbred and modified and
used as material for building of new species that
would better fulfill the conditions of re-forestra-
tion than any existing species.

Even botanists who thought that they fully
grasped the idea of Darwinian evolution looked
askance at such a suggestion.

It seemed to bid defiance to the laws of
heredity, as they understood them.

It appeared almost like an affront to Nature
herself to suggest that her handiwork might thus
be modified and improved.

Materials For Selection

And it may well be questioned whether this

[161]

LUTHER BURBANK

point of view would have been altered even to
this day had it not been for a conspicuous and
notable demonstration of the possibility of modi-
fying existing species of trees.

The demonstration was made when I took
pollen from the flower of a Persian walnut and
transferred it to the pistils of the California black
walnut.

Here were two species of trees so notably
different in form and shape of leaf and fruit and
color of wood that not even the most casual
observer could confound them. They were not
even natives of the same continent, and no botanist
would claim that they were as closely related as
are many species of forest trees that grow side by
side in our woodlands and maintain unchallenged
their specific identity.

Yet when these two trees were cross-pollenized
they produced fertile nuts, and trees of a new
order grew from these fertile seeds.

The barriers between these not very closely
related species were broken down, and a new type
of forest tree was produced that differed so mark-
edly from either parent that no one could con-
found it with either, and that excelled both in the
capacity for rapid growth so conspicuously as to
seem to belong not merely to a different species
but to an entirely different tribe of trees.

[162]

A Young Eucalyptus Tree

Several species of eucalyptus have been introduced
into California from the southern hemisphere. This speci-
men shows the remarkable symmetry and gracefulness of the eucalyp-
tus when grown by itself.

LUTHER BURBANK

The reader has already learned details of the
history of this Paradox walnut, and we shall have
something more to say of it in connection with a
further interpretation of the laws of heredity, in
a subsequent chapter.

Here I refer to it only in connection with the
demonstration it gave of the possibility that new
types of forest trees might be developed by hybrid-
ization and selection, quite as had been claimed in
the comment that aroused such skeptical and even
sarcastic response from the professional forester.

But, as I said, after this demonstration had
been made, it was no longer possible even for the
hidebound conservatist to deny the possibility that
forest trees, like other plants, are somewhat plastic
materials in the hands of the plant developer.

And in course of time it came to be recognized
— though even now the knowledge has scarcely
been acted on — that the new idea given by obser-
vation of the Paradox walnut could be utilized for
the practical purpose of supplying us timber trees
that might be expected to re-stock our woodland
in a fraction of the time that would be required for
the growing of trees of unmodified wild species.

The row of Paradox walnut trees which at
fifteen years of age were two feet in diameter and
towered as beautiful and symmetrical trees to the
height of sixty feet, standing just across the street

[164]

ON TIMBER TREES

from their Persian parent, which, at thirty-two
years of age was nine inches in diameter and per-
haps forty feet high, afforded an object lesson that
even the most skeptical could not ignore.

"If new trees are needed to make forests to
supply the place of those that your thoughtless for-
bears have destroyed," the trees seem to say, "why
not call upon me and my fellows?"

And to such a question there seems but one
rational response. The Paradox hybrid and its
fellows must be called upon to re-stock the rav-
aged timber lands of America. New hybrids must
be produced by the union of varied species of
pines, oaks, and elms, and other timber and orna-
mental trees, to give diversity to the landscape
and to supply different types of wood for the uses
of carpenter and cabinet-maker.

The Paradox walnut stood there — and still
stands — as the working model for a new order
of mechanism — a timber tree that shall be able to
re-forestrate a treeless region in half a human
generation with a growth ready for the axe and
saw of the lumberman.

The Materials At Hand

In preparing this new material for the making
of forest trees, it will be possible, no doubt, to
bring trees from foreign lands, either for direct
transplantation or as hybridizing agents.

[165]

•-*!&?'-

'

A Row of Eucalyptus Trees

-SSS^tuSi astonishingly rapid growth,
has such vitalitv that '£,/,«?,? ha?d andJurable. The tree

ON TIMBER TREES

Thus, as we have seen, one of the parents of
the Paradox walnut was a tree not indigenous to
America. But we may recall also that another
hybrid walnut, the Royal, which sprang from the
union of two indigenous species, the black walnut
of the Eastern United States and the black walnut
of California, rivals the Paradox in its capacity for
rapid and gigantic growth.

So it is obvious that we are by no means
reduced to the necessity of making requisition on
foreign lands for material with which to develop
our new races of quick-growing forest trees.

But, on the other hand, the plant developer is
always willing, like Moliere, to take his own where
he finds it. So if foreign species can be found that
will hybridize advantageously with our native
species, they will of course be welcomed. The
reader will recall that I have invoked the aid of
numberless exotic fruit trees and vegetables and
flower bearers in the course of my experiments in
plant development. There is every reason to
expect that equal advantage will result from the
utilization of forest trees from, let us say, Siberia
in one hemisphere and Australia in the other to
blend with the strains of American species.

In some cases it will be possible to bring the
foreign species and acclimate them without hybrid-
ization. This has been done with several species

[167]

LUTHER BURBANK

of eucalyptus which have been brought to Cali-
fornia from Australia and have proved a wonder-
ful addition to the ranks of our ornamental and
timber trees.

Everyone who visits California marvels at the
eucalyptus, and those of us who watch it year
after year marvel equally, because this tree has
capacity for growth that seems little less than
magical. No other trees, perhaps, ever seen in
America, with the exception of the hybrid walnuts,
have such capacity to add to their stature and
girth year by year as has the eucalyptus.

Moreover the eucalyptus may be cut down for
timber, its trunk severed only a few inches above
the ground; and it will send forth shoots that dart
into the air and transform themselves into new
trunks, each seeming to strive to rival the old one.
From the roots of the fallen giant spring a galaxy
of new giants, and each new shoot assumes the
proportions of a tree with almost unbelievable
celerity.

Add that the wood of the eucalyptus, notwith-
standing its rapid growth, is of the very hardest,
and the remarkable character of this importation
from the Southern Hemisphere will be more
clearly realized.

Unfortunately the eucalyptus is sensitive to
cold; otherwise it would at once otfer a solution of

[168]

In Mariposa Grove of Big Trees

The picture shows a Sequoia,

or big tree, in the midst of various pines. Note

the distinctive color, as well as the characteristic form of the Sequoia.

LUTHER BURBANK

the problem of re-forestration throughout the
whole of the United States.

Perhaps the eucalyptus may be made more
hardy by hybridizing and selection. If not, we
must take to heart the lessons it gives — in common
with the hybrid walnuts — as to the possibility that
a tree may show almost abnormal capacity lor
rapid growth and at the same time may produce
lumber of the hardest texture.

Hitherto it has generally been supposed that a
tree of rapid growth would as a matter of course
produce soft timber. The hybrid walnuts and the
various eucalyptus trees serve to dispel that
fallacy.

Native Materials

The one fault of the eucalyptus, its inability to
stand extreme cold, is likely to be shared by other
trees that are imported from the southern hemis-
phere or from sub-tropical regions of our own
hemisphere.

Although, as just suggested, it may be possible
to overcome this fault through selective breeding,
a long series of experiments will doubtless be
necessary before this can be accomplished. In the
meantime we shall be obliged to place chief
dependence, in all probability, upon our native
stock of trees, hybridized perhaps with allied
species of Europe and northern Asia.

[170]

Yellow Pine

There are said to be more species of conifers in California

than in all the rest of the world; and the very best of these,

from the standpoint of the lumber man is the yellow pine, here shown,

Note the absolutely straight trunk, holding almost the same

size to a great height. Observe also that this is a very

large tree, although not of course competing

with the Sequoia and the redwood.

LUTHER BURBANK

But, even so, there is no dearth of material.
America is richly stocked with forest trees. More-
over these represent, so the geological botanists
assure us, a flora of very ancient origin which has
shown its capacity to maintain itself through suc-
cessive eras during which there have been tremen-
dous climatic changes.

It follows that our native forest trees have in
their heredity the reminiscence of many and
widely varying environments. And by the same
token they have capacity for variation, and there-
fore afford exceptional opportunity for diversified
development.

It is not necessary here to analyze in great
detail the qualities of the different groups of forest
trees. A brief summary of the characteristics of a
few of the more important groups will serve to
suggest the abundance of native material, and to
give at least an inkling as to what may be ex-
pected, in the light of what was revealed by the
experiments with the walnuts, as to possibilities of
development of the different tribes.

Of course the great family of cone-bearers
stands in the foreground, represented by many
species, and known as the timber trees that give
us the pine lumber which has everywhere been the
chief material for the carpenter, and an important
foundation material for the cabinet-maker.

[172]

ON TIMBER TREES

We have but to recall the giant sequoia and
redwood of California, the largest trees existing
anywhere in the world, to be made aware of the
possibilities of growth that are present in the racial
strains of the family of cone-bearers. And even if
these giants shall be regarded as representatives
of an antique order that has outlived its era, there
remain numerous pines and firs and hemlocks of
magnificent proportions to test the skill of the
plant developer for their betterment.

Moreover there is every probability that red-
wood and big tree may be crossed, and a variety
produced that will be adapted to the new condi-
tions, and which will outgrow all other trees.

Nothing could be easier than to cross-pollenize
members of this tribe, inasmuch as the pollen is
produced in the utmost profusion, and the pistil-
late flowers are exposed when mature in the
nascent cones awaiting fructification. That cross-
fertilization occurs among the wild trees through
the agency of the wind is a matter of course.
Doubtless there are hybrid species of pines and
their allies, everywhere often unrecognized or
classified as good species. Quite large forests
mostly composed of hybrid cypresses are found in
California, and the oaks are known to hybridize
frequently; also the eucalyptus trees of various
species.

[173]

A Petrified Pine

This tree is one of a large number in the petrified forest

near Santa Rosa. The trees were overthrown by an earthquake

and covered with volcanic ashes at a remote period of the past, and

many of them became perfect petref actions. A forest of large

modern trees grows from the soil overlying the petrified forest.

ON TIMBER TREES

If study were made of individual conifers in
any forest region where different species are
found, it would doubtless be possible to secure by
mere selection new races that would admirably
serve the purposes of the forester.

But of course still better results may be ex-
pected when hand-pollenizing is carried out intel-
ligently, and the racial strains of different species
of conifers are blended and tested to find just
what are the best combinations.

It would be nothing strange if among the
hybrids there should be found one or more varie-
ties that will attempt to rival the Sequoia itself in
giantism, and that will quite outrival it in rapidity
of growth.

What the pines are as producers of white and
relatively soft wood of straight grain and uniform
texture, the members of the great family of oaks
are as producers of wood of hard texture, irregu-
larly grained and knotted, but capable to taking
on a polish and serving almost every essential
purpose of the cabinet maker.

The most famous of oaks, doubtless is the
typical British species, but the American white oak
is a close second. Perhaps these two might be
hybridized. If the hybrid thus produced were by
any chance to show the capacity for rapid growth
that the hybrid walnuts have shown, while retain-

[175]

LUTHER BURBANK

ing the hardness of texture of its parents, as the
hybrid walnuts do, the tree thus produced would
by itself go far toward solving the problem of
re-forestration. The oaks quite frequently hy-
bridize in a state of nature.

Granted a producer of soft white wood such as
probably can be made by combining the white pine
with some of its allies; a producer of hard cabinet
wood such as a hybrid between the British oak and
the American white oak would probably consti-
tute; and the hybrid walnuts already in existence
as producers of woods of the hardest and finest
texture for cabinet purposes — granted further
that the other new trees have the capacity for
growth which the hybrid walnuts show — and a
triumvirate of trees would be attained that could
be depended on to go forth and gladden the de-
vastated hillsides and valleys with trees that would
jointly meet every need of carpenter and cabinet
maker, adding incalculable billions to the wealth
of our nation.

And of course we need not by any means con-
fine attention to these few most typical trees.
There are beeches and chestnuts that are near
relatives of the oak, each of which serves its own
particular purpose as the provider of wood having
unique quality. The beech, for example, is prized
by the chair maker for his furniture, and by the

[176]

A Young Giant Sequoia

This beautiful evergreen tree is a young Sequoia, about
six years old, growing in Mr. Burbank's garden. Note the com-
pact growth of branches from the very ground. Contrast this young
tree with the old Sequoia shown in the next picture.

LUTHER BURBANK

turner for the making of carpenter tools and such
like instruments. The chestnut makes railroad
ties that are thought to have no equal and tele-
graph poles of requisite strength and straightness.

Then there are other families that have their
valued representatives. The hickories have al-
ready been referred to. The maples must not be
overlooked, as they furnish highly prized white
woods to the cabinet maker. The tulip tree sup-
plies a light-colored wood used by cabinet maker
and coach builder. The basswood or linden gives
a wood of peculiar fiber that meets the needs of
carvers and instrument makers. The willows and
their allies; members of the birch family; the
buttonwood tree or sycamore; and the locusts and
their allies are other native trees that are of value
as they stand and are well worth developing.

The plant experimenter who works with these
different trees, being guided by their botanical
affinities, but making careful tests even where he
doubts the possibility of hybridization, will be
almost certain to have his efforts rewarded by the
production of some trees of new varieties that will
not only duplicate the unexpected qualities of the
hybrid walnuts, but will doubtless also reveal un-
predicted traits that will give them added value.

Patience will be required in carrying out the
work, for the tree is long-lived and experiments

[178]

ON TIMBER TREES

in its development are quite different from those
in the development of annual plants. Yet some-
thing of the probable results of an experiment can
be judged even from observation of seedlings in
their first year. And by hurrying the hybrid plants
by the method of grafting, it will be possible
greatly to shorten the generation.

Still it is not to be denied that the work of
developing new races of trees is one that should
preferably command the attention of the younger
generation. In particular, it should be carried on
under government supervision, as part of the great
work of re-forestration, the necessity for which
has only in recent years been clearly realized by
those in authority or by the community in general.
Messages from the Past

The oft-cited hybrid walnuts supply us with
tangible evidence of the possibility of developing
new races of trees having much-to-be-desired
qualities of rapid growth, through hybridization
of the existing species.

Such evidence, as I have suggested, doubtless
is more forceful and convincing than any amount
of theoretical argument. But it may be of interest
to support this evidence, and in so doing to reveal
additional reasons for belief that the same princi-
ples will apply to other forest trees, by recalling
briefly the story of the vicissitudes through which

[179]

» *■*. ' 1-lr _.

The Largest Tree in the World

This giant Sequoia, growing in the Mariposa Grove, in the
Yosemite National Park, is known as the "Grizzly Giant." It is
,34 feet in diameter and 225 feet high. It is estimated to contain more
than one million feet of lumber. The first limb is iOO feet from
the ground, and 6 feet in diameter. Doubtless the tree or-
iginally had limbs all the way from the ground, but
the lower ones have died in the course of the
ages that mark the life of this extraor-
dinary tree. Observe the man
standing near the tree, by
way of contrast.

ON TIMBER TREES

the existing trees have passed and through which
the diversified hereditary factors were implanted
in their racial germ plasms.

A knowledge of this story we owe to the geolog-
ical botanists. They have sought diligently in the
rocks for fossil remains, and by joint effort, search-
ing all around the world, have been able to repro-
duce a picture of the main story of the evolution
of existing forms of vegetable life.

It is by recalling the story which they tell us,
and thus alone, that we are enabled somewhat
clearly to apprehend the possibilities of variation,
and through variation of so-called new develop-
ment— consisting essentially of the re-combination
and intensification of old ancestral traits — that we
have witnessed in the case of many tribes of plants
in the course of our experiments.

A brief resume of this story of plant life in the
past, with particular reference to our own flora,
will serve in the present connection to explain why
there is every warrant for believing that each and
every one of our forest trees contains submerged in
its heredity the potentialities of a development of
which its exterior appearance gives but faint
suggestion.

It appears that there is full warrant for the
belief that the modern flora originated in the
northern hemisphere, and probably in the region

[181]

LUTHER BURBANK

of the north pole, During the so-called Mesozoic
age, the conditions of the northern hemisphere
were those that would nowadays be described as
tropical or sub-tropical. There were palms grow-
ing in Europe, and such species as the sequoia,
the plane trees, maples, and magnolias grew even
at a relatively late period as far north as the
seventieth degree of latitude. Remains of conifers
have been found within nine degrees of the pole
itself; remains of palms in Alaska coal measures,
and of the sassafras along the western coast

At this early period the flora of the entire
northern hemisphere was, as regards its trees,
essentially comparable to the existing flora of
America to-day.

There were oaks and beeches scarcely dis-
tinguishable from existing species.

There were birches and planes and willows
closely related to the living species known as Salix
cambida.

There were laurels not unlike their modern
representatives, the sassafras and cinnamon tree,
and myrtles and ivies that are represented by
existing descendants of allied forms.

And there were magnolias and tulip trees of
which the existing tulip tree of the United States
is an obviously direct and not very greatly modi-
fied descendant.

[182]

Another View of the "Grizzly Giant."

Th,'« wonderful tree leans more than 18 feet out of the

P.SSUSH T^sVain thus put upon ^roo^^tbe

tremendous, but they show no sign of j.jn»; 2n\ldnotmain-

of aae vet there seems no reason why it should not main

tain its supremacy in the Mariposa Forest for a good

taiVanycentZesyto come. Almost the entire drama

of the history of civilized man has been

acted since this tree was a seedling.

LUTHER BURBANK

All these trees grew far to the north, and
luxuriated, as has been said, in a temperature that
we of to-day would call sub-tropical, but which the
inhabitants of that time, had there been a human
population, would have described as arctic; for in
that day it is probable that the north pole was
tilted far toward the sun, and that the conditions
that we now think of as tropical existed only in
the region of the pole itself.

Then there came the slow progressive period of
refrigeration. The tropical climate of the pole was
succeeded by an age of ice, and the successive ice
sheets slowly pressed southward, driving the
plants no less than the animals before them along
all parallels of longitude, until the flowers and
faunas that intermingled in the arctic region were
scattered along diverging paths to people the
continents separated by the wide stretches of the
Atlantic and the Pacific oceans.

It may seem strange to speak of plants fleeing
before the ice sheet. But it must be understood
that the plant is a migratory being, when consid-
ered as a race, notwithstanding the stationary
habit of the individual. Plants put forth mobile
seeds, and devise many strange ways of insuring
their wide dissemination. They are always seek-
ing new territories, and, granted proper conditions,
always finding them.

[184]

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LUTHER BURBANK

And it was only such plants as could migrate
with relative celerity that were able to maintain
existence and escape extermination by fleeing
southward when the era of cold succeeded to the
warm era in the arctic regions and when the arctic
chill gradually spread southward and encom-
passed all the higher and middle latitudes of the
northern hemisphere.

The plants that chanced to flee southward along
the land surface that we now term Europe found
their further flight checked when they reached the
stretches of mountains extending east and west
that we now term the Alps. Here thousands of
species made a last stand and ultimately perished.

But the plants that were fortunate enough to
choose the other avenues of escape, passing down
across the land surface that we now term America
and Asia, were not obstructed in their flight. In-
deed, the long ranges of the Appalachians and
Rockies and Sierras in particular served, as it
were, to guide the line of march and aid the flight.

So the American species made their way to the
region of the gulf, and some of them even to the
southern continent. And when the ice sheet finally
receded, they were able to make their way north-
ward again, though never to their former habitat;
whereas Europe was treeless until the plant life of
Asia spread westward to re-people it.

[186]

A Petrified Redwood

This is one of the largest and most perfectly preserved
specimens hitherto exhumed at the petrified forest, near Santa
Rosa. It is a good sized specimen of the redwood (Sequoia semper-
virens). Its entire substance is solid stone, but the ap-
pearance of the original texture of wood and
bark is wonderfully preserved.

LUTHER BURBANK

Such is the explanation that the paleo-botanist
gives us of the fact that the indigeneous vegetation
of America to-day is closely similar to that which
stocked the sub-arctic regions of the entire north-
ern hemisphere in the geological period known as
the Mesozoic — a period that seems infinitely
remote when measured in terms of human history,
yet which in the scale of time as measured by the
geologist is relatively recent.

Such trees as the sequoia, we are told, are sur-
vivors of that ancient regime that chanced to find
hospitable shelter on the western slopes of the
Sierras. Similarly the tulip tree of the east, with
the blossoms that seem anomalous for a tree,
should be regarded as the souvenir of a past age —
a lone representative of vast tribes that once flour-
ished in tropical luxuriance in regions that now
give scant support to moss and lichen and stunted
conifers.

All in all, we are told, the remaining vegetation
of to-day, varied though it seems, is but a scant
reminiscence of that of the period preceding the
ice ages. Only a few species, relatively speaking,
were able to make their migration rapidly enough
to escape destruction. These included a certain
number, like the sequoia and the tulip tree, that
were able to reach coigns of vantage that per-
mitted them to exist without changing essentially

[188]

ON TIMBER TREES

from their sun-loving habit. But in the main the
tribes that escaped destruction were those that
developed a hardiness that enabled them to with-
stand extremes of temperature not far beyond
the limits of the ice sheet. Others made their way
northward again so soon as the ice sheet receded.

And as the climate of ensuing ages, after the
successive periods of intense refrigeration, every-
where retained, throughout the central and eastern
portions of America, curious reminiscences of both
the tropical and the arctic, the plants that finally
repopulated the devastated territories were those
that had learned, through the strange vicissitudes
of their ancestors, to thrive where the thermometer
in summer might rise to the one hundred degree
mark, and where in winter the mercury might
freeze.

Such are the conditions under which pines and
oaks and willows and beeches and black walnuts
and allied trees exist to-day in the regions of
northern America where they flourish.

They can withstand the glare of a tropical sun
in summer because their ancestors reveled in a
tropical climate. And they can withstand equally
the arctic cold of winter because their ancestors of
other ages were forced to subsist under arctic
conditions.

The versatile tree that, thanks to the racial

[189]

Natural Grafts at the Petrified Forest

This tree is a live oak growing from the soil overlying
the petrified forest. It is of peculiar interest because its
branches form two natural arches through having grown together, con-
stituting natural grafts. We not infrequently see the trunks of
trees thus united, but such union of branches is very unusual.

ON TIMBER TREES

recollection of these vicissitudes, can adapt itself
to the inhospitable conditions of our modern cli-
mate are but dwarfed representatives of ancient
races of giants. To preserve life at all it was
necessary for them to conserve their energies; and
gigantic growth is feasible only for plants that can
send their roots into rich, well watered soils and
can likewise draw sustenance perennially from
the atmosphere, unhampered by long periods of
dormancy when life itself is threatened.

But these dwarfed races carry in their germ
plasm, submerged but not eliminated, factors for
giant growth; factors for such development as
would adapt them to life in the tropics; factors
also for such development as would adapt them
for life in the arctics.

Their hereditary factors, in a word, are as
varied as have been their past environments. So,
as I said, what each tree is exteriorly gives us but
faint suggestion of what it might be were its un-
realized hereditary possibilities to be made
actualities.

So far as we know at present, the only way in
which these unrealized possibilities may in any
conspicuous measure be brought out is by hybrid-
izing species that have so far diverged that they
lie almost at the limits of affinity. By such union
of hereditary factors that have long been dis-

[191]

LUTHER BURBANK

united, racial traits that are reminiscent of the
old days when the northern hemisphere enjoyed a
tropical climate may be revived, and a tendency
to repeat a gigantic growth that characterizes
ancestors vastly remote will be revealed.

Such, I take it, is the explanation of the strange
and otherwise inexplicable phenomena of gigant-
ism manifested by my hybrid walnuts. And such
is our warrant for believing that all other species
of native trees have possibilities of development
that are unrevealed in the exterior appearance of
their present-day representative, and that can be
revealed, so far as we know, only by hybridization.

— New hybrids must be pro-
duced by the union of varied
species of pines, oaks and
elms, and other shade and
ornamental trees, to give di-
versity to the landscape and
to supply different types
of wood for use of car-
penters and cabinet-makers.

The Production

of A

Quick-Growing Walnut

The Burbank Royal and Other Experiments

MY hybrid walnuts, already known to the
reader as the Paradox and the Royal,
were first publicly announced in my
catalog called "New Creations in Fruits and
Flowers", in June, 1893.

The hybrid walnuts themselves were then five
or six years old and the Royal had borne fruit, so
that a photograph of its large-sized nut could be
given. The Paradox, on the other hand, although
it had flowered for several seasons, had produced
no fruit. It was supposed, therefore, that it would
be impossible to reproduce this hybrid from seed.

In subsequent years, however, the Paradox
proved its capacity to produce fertile fruit, al-
though it was never a free bearer. And in my
supplementary catalog of the year 1898, 1 was able
to offer seeds of the Paradox for sale, and to make
a statement as to the manner of seedlings that

TVolume XI — Chapter VII]

LUTHER BURBANK

might be expected to grow from these seeds. The
statement, in view of the date when it was printed,
has somewhat exceptional interest in the light of
later developments, so I quote it here.

It was as follows :

"The six beautiful specimens of this hybrid
growing on my home place have been objects of
admiration to all who have seen them.

"Young trees could have been sold at almost
any price, but, having no time to raise them, otter
this season's crop of nuts which will be a great
surprise in producing about one-third of a new
type of the broad-leaved Persian walnuts, one-
third of a new type of the California black walnut,
and about one-third combined, as in the original
tree."

The "original tree" in question was, of course,
the hybrid called the Paradox, produced by cross-
ing the California walnut and the Persian walnut.
So the seedlings, the character of which is pre-
dicted in the paragraph just quoted, would of
course represent second generation hybrids from
this cross.

I make the quotation here, carefully specifying
the date at which the original was printed, because
there is a certain interest in knowing that tests
made prior to this time with the seeds of the hy-
brid walnut had clearly revealed to me the fact

[194]

ON THE QUICK GROWING WALNUT

that "about one-third" of the second generation
hybrids would revert toward one parent, while
another third would revert toward the other
parent, the remainder being intermediate in char-
acter, and in this corresponding to the first genera-
tion hybrid that was their parent.

This implies a fair understanding of the com-
bination of characters of the two parent species
in the first generation hybrid, and the segregation
and recombination of these characters in the sec-
ond generation hybrid. It will be noted also that
the distribution of these characters in the second
generation (as predicted on the basis of my obser-
vation of earlier seasons) was essentially that
which has come to be familiar everywhere within
recent years as the typical distribution of charac-
ters among second generation hybrids in what is
now known as Mendelian heredity.

To be sure the figures given are only approxi-
mate, nor have I in any of my experiments endeav-
ored to keep accurate count of the precise
numbers, the large scale on which I operate mak-
ing this scarcely practicable — but the close approx-
imation of the rough estimate that I made to the
precise figures that have been determined by more
recent investigations, sufficiently attests the accur-
acy of the observations on which the estimate was
based.

[195]

LUTHER BURBANK

And, figures aside, the essential principle of the
segregation of characters, and their redistribution
into three essential groups, one representing each
parent, and one combined as in the first generation
hybrid, is as clearly stated as can be desired.

The interest of all this hinges solely on the fact
that the statement was published in 1898, based
obviously on observations made prior to that date;
at a time, therefore, when no one living had the
remotest knowledge of the discovery made by
Mendel more than thirty years before. Mendel
himself died in 1884, and the rediscovery of his
work was not made until a year or two after the
date of my catalog, just quoted.

And I may fairly assume, I believe, that there
were few, if any, botanists or plant developers in
the world, at the date of this publication, who had
any such clear conception of the meaning and
interpretation of the prediction contained in the
quoted paragraph as my own original observa-
tions had given me.

In point of fact, the observation on the seeds
of the Paradox walnut, as here quoted, was made
quite casually.

I did not put it forward as constituting a new
pronouncement in heredity, because it simply rep-
resented a specific application of a general truth
regarding the tendency of heritable characters to

[196]

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>-4?^.^i A* wis"-

A Row of Paradox Walnuts

The paradox walnut, it will be recalled, is a hybrid pro-
duced by Mr. Burbank, through cross pollenizing the Persian
walnut and the California black walnut. The picture shows a row
of very young Paradox walnuts growing beside Mr.

Burbank's gardens at Santa Rosa.

LUTHER BURBANK

be segregated and recombined in the second gen-
eration hybrids that had come so often under my
observation that it had become a commonplace to
me many years before the publication of this
catalog in 1898.

I have elsewhere stated that the matter had
been the subject of controversy with a good many
of the leading botanists and horticulturists of the
world, and that during the period of perhaps fif-
teen years prior to the rediscovery of Mendel's
experiments, I seemingly stood in a minority of
one in the belief that such segregation and redis-
tribution of characters in the second generation
hybrids is the usual and all but habitual method
of inheritance.

After DeVries and his fellow-workers had
come upon Mendel's earlier publication and made
it known to the world, the matter was no longer
in dispute.

But then the neophytes who had so long refused
to listen to my claim were disposed, after the man-
ner of neophytes, to become over-enthusiasts, and
some of them at least thought that the principle
of the segregation of heritable characters in the
second generation was one that must supplant all
other principles of heredity, reducing questions of
inheritance to such simple formula that the veri-
est tyro could master them, and having them in

[198]

ON THE QUICK GROWING WALNUT

hand, could go into the field and create new forms
of plant life at will.

And because I ventured to point out that the
essential principles that now came to be spoken of
as Mendelian had been the guiding principles of
my experiments for at least twenty years before
Mendelism was heard of, I was denounced in some
quarters as reactionary, the fact being quite over-
looked that the essential principles involved had
been discovered by me quite independently; ex-
ploited by me in connection with many hundreds
of species; given publication by me prior to the re-
discovery of Mendel's forgotten paper; championed
by me against the opposition of all the leading
authorities of the world; and that therefore
the aspect of heredity in question might with full
propriety have been named "Burbankian" instead
of "Mendelian", were it not that Mendel's discovery
had priority because it was published so long ago
as 1863, whereas my independent discovery of the
principle was not made until almost twenty years
later.

Even at that, however, I had had full twenty
years priority over any one else except Mendel in
the recognition of the principle.

Therefore, as I just intimated, I have found it
a trifle disconcerting to be heralded as reactionary
and as scouting the essential principles that I

[199]

LUTHER BURBANK

ardently espoused during a period of at least six-
teen years subsequent to the death of Mendel,
during which they had no other champion.

What I have deprecated, however, in recent
years, is the over-enthusiasm of certain alleged
followers of Mendel, who have entertained what I
conceived to be a misapprehension as to the real
significance of "unit characters", and who, mis-
guided by a narrow range of experiments, and
lacking the breadth of view that comes with wider
experience, have supposed that all heritable char-
acters might be classified as fixed and unvarying
entities that are transmitted in accordance with
the Mendelian formula.

Fortunately, a good many former holders of
this biased and inadequate view have seen its in-
sufficiency, and already there is a tendency to
react from it, evidenced in the writings of some of
the leading Mendelians; and, coupled with this, the
tendency to take a broader view of heredity and to
understand that there are countless heritable char-
acters that do not Mendelize in any tangible or
demonstrable way; that "unit characters" are
themselves made up of subordinated characters;
that new "unit characters" from time to time ap-
pear, whereas old ones that at one time Mendelized
are finally so fixed that they blend with the older
structure of heredity and no longer present the

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phenomena of "dominance" and "recessiveness" —
in a word, that heredity is a somewhat larger term
than Mendelism, and that the biologist or botanist
or plant developer who would gain a really clear
conception of the situation must clearly distinguish
between the lesser term and the greater, although
at the same time recognizing that one is an essen-
tial sub-structure of the other.

So Darwinian heredity, which recognizes the
heritability of whole coteries of characters that are
too profoundly lixed to Mendelize, is again receiv-
ing recognition; and the multitude of special
studies of the past decade that were inspired by
the rediscovery of Mendel's work and by the ex-
ploitation of his formula will take their place as
interesting additions to the minutia of the scheme
of heredity, without being supposed by any one,
except here and there a victim of mental strabis-
mus, to represent the full measure of the great
mysteries of inheritance.

We have had occasion in successive chapters to
present again and again illustrations of the type of
hereditary transmission that lends itself to classi-
fication under the Mendelian notation. We shall
catch further glimpses of it before we are through.
Here it seems worth while, in connection with the
story of the hybrid walnuts, to attempt a more
comprehensive view of the entire field of heredity,

[202]

ON THE QUICK GROWING WALNUT

endeavoring to gain a clear notion as to just what
are the underlying principles that determine
whether or not a certain heritable character or pair
of characters shall Mendelize; and in so doing we
may correlate our earlier studies, and secure a
clearer notion of the underlying principles of
evolution, and of the origin and development of
species, than could perhaps have been gained with-
out the aid of the illustrative cases that have been
presented.

Natural Selection

In the preceding chapter we briefly reviewed
the story of the vicissitudes to which plant life has
been subjected in the course of recent geological
eras. We were concerned there with the elimina-
tion of unadaptable species rather than with the
evolution of adaptable ones.

But it should of course be understood that the
same principle of natural selection applies to the
preservation and to the weeding out of species.

In the case under consideration, it was the
changed climatic conditions, through which the
northern hemisphere was transformed from a re-
gion of tropical heat to one of arctic cold, that
resulted in the destruction of countless species,
leaving only a tithe of the original number to con-
stitute the flora of the temperate zone in our own
day.

[203]

LUTHER BURBANK

It is easy to see how the altered conditions of
temperature made the struggle for existence un-
duly hard for many species, because there is a
tangibility about the coming of a glacial period
that finds an analogy in the coming of winter in
the regular sequence of seasons. The fact that a
plant which thrives in the summer in northern
regions cannot survive through the winter unless
protected is so familiar as to give us a concrete
example of the destruction of species through
changed climatic conditions in the geological eras.

But the struggle for existence that goes on all
about us among plants of every species is so much
less tangible that it is not so easily visualized.

Not unlikely the climate of the northern hemis-
phere is changing now year by year as rapidly as
it ever changed in any era of the past.

The alteration is so slight within the span of
any single life as to be unappreciable. But when
we look back, aided by the studies of the geologist,
andthinkof thechange of climate that transformed
the flora of the Mesozoic time, we see things clus-
tered in perspective, and in our mental vision the
picture of the transformation from tropical to
arctic conditions corresponds rather to the onset of
winter in our annual experience, than to the true
picture of a change of climate that required not
merely centuries but millenniums.

[204]

ON THE QUICK GROWING WALNUT

In the same way we conceive of the evolutionary
changes through which new species were evolved
in the past as having been relatively sudden. I
have already referred to the difficulty with which
the average mind can grasp the idea that precisely
the same sort of change in animal and vegetable
forms is taking place to-day that has taken place
in all other stages of evolution.

It was one of the great merits of Darwin's expo-
sition of the "Origin of Species", that he gave de-
tailed illustrations of the struggle for existence,
and brought tangibly before the minds of thought-
ful people the conception that each race of beings
is more or less in competition with every other
race, and that the race that is adaptable enough to
adjust itself to new conditions is the only one that
stands any prospect of survival.

The idea of the progression of the normal
increase of living creatures in geometrical ratio
and of the resulting over-population of any terri-
tory by the progeny even of a single pair, if there
were no counteracting factors, was of course re-
ceived by Darwin from Malthus. But the applica-
tion of that idea to all races of animals and plants,
and the logical deduction from its application
which first made possible anything like a clear
understanding of the reason why vegetable and
animal races have evolved, was due to Darwin.

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Alfred Russell Wallace conceived the same idea
independently, and must always be credited with
a share in the discovery.

But of course it was Darwin's exposition that
gave the subject general vogue, and the scheme of
heredity that it connotes is with full propriety
spoken of as Darwinian evolution.

The essentials of this scheme of heredity may
be stated in a few words, as follows: Animals and
plants tend to increase in geometrical ratio. If
unopposed, the progeny of a single pair of animals
or an individual plant would soon populate and
over-populate the entire earth. Opposition to such
over-population comes from the rivalry of other
animals and plants. The struggle for existence
thus induced puts a premium on the individual
animal or plant that is better able than its fellows
to seek means of sustenance. Such an individual
will, on the average, live longer and produce more
offspring than an individual less well adapted to
its surroundings.

The preservation of these favored individuals
and their progeny may be described in a phrase
as "the survival of the fittest."

The natural processes that determine such sur-
vival on one hand, and the destruction of the less
fit on the other, may be spoken of as constituting
"natural selection."

[207]

LUTHER BURBANK

This term, natural selection, has obvious pro-
priety because it connotes a process closely akin in
its results to the artificial selection through which
man determines that certain races of animals and
plants under domestication shall be preserved, and
that others shall be destroyed. But artificial selec-
tion is after all only a phase of natural selection,
in which man becomes an active influence or a
deciding element in environment.

Because of man's power to transform the con-
ditions of soil, to supply artificial heat, and to
bring together and hybridize plants and animals
that would not come in contact in the state of
nature, the results of artificial selection, epitomiz-
ing within certain bounds the results of natural
selection, may be produced with unexampled
celerity.

Man, for example, eliminates a species in a few
decades, where nature would have found no way of
correspondingly rapid elimination. The black
walnut, for example, has been almost extermi-
nated throughout eastern America because man
prized its wood for the making of furniture. But
for the presence of civilized man the black walnut
would doubtless have maintained its position for
ages to come, just as it had maintained it through-
out the ages of the past.

Yet we must not forget that on occasion there

[208]

ON THE QUICK GROWING WALNUT

may be natural methods of elimination that will
single out a species and destroy it as expeditiously
and as certainly as man could accomplish that
end.

A case in point is furnished by the chestnut,
which, as we have seen in a recent chapter, has
been singled out in certain regions of the Eastern
United States by a fungoid blight that leaves no
chestnut alive in the regions over which it spreads.
Yet this blight seems powerless to effect any other
species.

Here, then, we have an example of a destructive
agency of an unpredicted kind that gives an ex-
ample of the rapid destruction of a species,
through natural selection, because that species
could not rapidly enough adapt itself to a new
condition.

Given time, the chestnut would doubtless de-
velop immunity to the fungoid pest. But time was
not given it, and hence it was destroyed.

This present-day illustration perhaps gives as
vivid an impression of one of the more tangible
ways of the operation of natural selection as could
be desired. But we must suppose that such drastic
measures as this are rather exceptional and that
in general the processes through which species are
eliminated are more subtle in their operation,
although their ultimate results are no less striking.

[209]

Nuts of the Royal Walnut

The Royal hybrid, unlike the Paradox, bears nuts in ex-
traordinary profusion. Moreover, these nuts are of very large
size, far surpassing those of the parent forms, at it illustrated in
the succeeding picture.

ON THE QUICK GROWING WALNUT

All this has to do, however, with the destruc-
tion, rather than with the evolution of species.

I have already said that the principles of nat-
ural selection apply with equal force, and seem-
ingly with entire impartiality, to the destruction
and to the preservation of species.

But it is obvious that mere preservation of
species does not necessarily imply also the evolu-
tion of species. Natural selection might give a
dominant position to a particular species, and pre-
serve it for indefinite periods without essential
change.

But this could only occur in case the condi-
tions of environment themselves remained essen-
tially unchanged.

It is fundamental to a clear understanding of
evolution to realize that in a changing environ-
ment, under natural conditions, no species could
be preserved unless it proved adaptable.

Indeed, the more perfectly adjusted the species
might be to its environment at a given period, the
more certainly must that species be destroyed
should the essential conditions of the environment
change.

The great penalty of specialization is the
danger that attends it from this source. It is held
that the species that were eliminated when the
great climatic change occurred to which we have

[211]

LUTHER BURBANK

more than once referred were those that were the
most highly specialized.

But, on the other hand, a species that is able
to change in such a way as to adapt itself to new
conditions stands at least a chance of being pre-
served, however widely the environment may be
altered. And, in point of fact, most species in a
state of nature have a considerable measure of
adaptability. Individual variation is the universal
rule, and such variations are accentuated by nat-
ural selection very much as the plant developer
accentuates them by artificial selection. So the
plants and animals in a state of nature are plastic
material, and under changing conditions of en-
vironment which represent probably the usual and
normal condition of things, they are constantly,
even if slowly, being modified. And of course
such modifications, when they have been sufli-
ciently added to, alter the character of the species
altogether.

Which is only a detailed and roundabout way
of saying that species are evolved and transformed
into new species under the influence of natural
selection.

But whoever considers this matter attentively
will come presently to realize that in any such
analysis of the operation of natural selection in
the evolution of species as that just suggested,

[212]

ON THE QUICK GROWING WALNUT

there is an underlying assumption to the effect
that the various modifications of the individual
are transmitted to the offspring of the individual.

Unless such is the case, it is clear that there
could be no such thing as the evolution of new
species. It would avail nothing for the progeny
of an individual that this individual wras well
adapted to its surroundings, unless the said
progeny inherit the characteristics that made such
adaptation possible.

There is no logical escape from that conclusion.
Whatever our conception of the mechanism of
heredity, or of the exact manner in which the
transmission of variation occurs, no one can be an
evolutionist who does not believe that acquired
characters are transmitted through heredity.

There was a school of biologists who gained
great prominence a few years ago, who denied the
possibility of the transmission of acquired traits.
Throwing logic to the winds, they based their
denials on a metaphysical interpretation of certain
observed microscopic structures within the germ-
cell. These same biologists, while denying that
acquired traits could be transmitted, were at the
same time ardent upholders of what they called
Darwinian evolution.

But such a paradoxical contention must of
necessity fail to maintain itself for any consider-

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able period. In the last analysis, people are able
to put two and two together and discover that the
result is four. And in the course of time even the
most illogical biologists were forced to see the
elemental truth of the proposition that new char-
acters acquired by an individual organism must be
transmissible, else there could be no such cumu-
lative change as that which results in the trans-
formation of a species in new adaptations to its
surroundings.

In other words, if acquired characters are not
transmitted, there can be no organic evolution.

But a good many of the former adherents of
this paradoxical view have abandoned their illog-
ical position unwillingly, and even now are only
willing to admit that such acquired characters are
transmissible as are imprinted first on the germ
plasm, and not on the body of the parent organism.

The contention really reduces the entire matter
to a question of definition. It is virtually a dis-
tinction without a difference, when we reflect that,
at all events, in the case of the plants, germ plasm
and body plasm are everywhere associated, so that
we must suppose that if there is really a distinction
between the two, it is a distinction within the sub-
stance of the individual cell, as the plant body
contains both body plasm and germ plasm. Our
earlier studies have shown that we are forced to

[215]

LUTHER BURBANK

this conclusion; and obviously if this interpreta-
tion of germ plasm be accepted, it is a mere quib-
ble as to whether the change or modification of an
individual plant involves primarily the germ plasm
or whether it involves the body plasm of the same
cell as well.

Of course such mere incidental modifications of
an individual as have to do with injury of its parts,
the laceration of tissues, or the like, cannot be
supposed to have any influence in heredity.

If such accidental modifications are heritable,
the entire scheme of inheritance would become
chaotic.

The modification that is heritable must be one
that involves the constitution, so to speak, of the
plant; such modification as would be brought
about by changed conditions of nutrition, or by an
altered temperature. A certain amount of experi-
mental proof is already in hand that such modifi-
cations as these may be inherited. And if the
opponents of the theory of the transmission of
acquired traits can get any comfort out of the
claim that such modifications directly effect the
germ plasm, we need not wish to rob them of that
cold comfort.

Details as to the special manner of inheritance
aside, we may accept it, I think, as the only logical
conclusion from a wide survey of the facts of her-

[216]

ON THE QUICK GROWING WALNUT

edity and evolution, that all modilied characters
that effect the constitution of the individual are
heritable. Even the slightest modification of
structure due to altered nutrition, to changed tem-
perature, or the like, probably makes its influence
felt on the next generation in exact proportion to
its value in the great complex scheme of charac-
ters with which it is associated.

But this statement must not be misinterpreted.
It must not be supposed that any minor modifica-
tion of an individual can influence, except in an
infinitesimal way, the inheritance of the offspring
of that individual.

For the new modification will be, in the nature
of the case, only as an alien drop or two in an
ocean of hereditary tendencies.

Or, stated in somewhat more modern terms,
the hereditary factor that represents the new mod-
ification will be as one minor factor among thou-
sands or perhaps millions of pre-existing factors.

If we revert to an earlier illustration, in which
we thought of the germinal nucleus as a piece of
architecture made up of multitudes of factors of
heredity, we may think of the new factor as one
added brick in a structure of palatial proportions,
made up of thousands of bricks.

Yet it is by the cumulative effect of such minor
modifications, we may well believe, that evolution

[217]

LUTHER BURBANK

has been brought about, and that in the long lapse
of ages, the highest forms of existing plants have
been built up by successive stages of inheritance
from the lowliest single-celled organisms.
The Status of Mendelism

In the large view, then, whereas it will be rec-
ognized that all acquired traits have their influ-
ence in heredity, yet it will also be recognized thai
the vast sum of qualities that are of less recent
origin has preponderant influence, and that the
racial characteristics as a whole are overwhelming
in their power as against any individual modifica-
tions.

Yet, to complete our picture, we must recognize
also that nature is not conservative, as she is
commonly said to be, but is highly progressive. It
could not be otherwise, in a world in which the
natural environing conditions are constantly
changing.

The basal law of evolution, as we have seen, is
that the unchanging, the conservative organism, is
doomed. It is only the progressive, the changeable,
the plastic organism that can hope to maintain
itself and perpetuate its kind indefinitely.

The price of specific life is that the species
shall not maintain its identity.

And this interpretation of the situation gives a
clew, so it would seem, to that important and inter-

[218]

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LUTHER BURBANK

esting aspect of heredity to which we referred at
the beginning of this chapter — the phase com-
monly spoken of as Mendelism. The essential
characteristic of this aspect of heredity, as we have
pointed out over and over, is that heritable charac-
teristics are transmitted in a sense independently
one of another, in such a way that they may be
segregated and put together again in new com-
binations in successive generations.

The detail within this scheme of transmission,
with which Mendel himself was chiefly concerned,
and which absorbed the attention of his followers
until it was found that there was need of taking a
wider view, was involved in the phenomena of
dominance and recessiveness. Mendel found, for
instance, as we are aware, that when a tall pea
vine was crossed with a short one the hybrids of
the first generation were all tall, because, as he
said, tallness was dominant and shortness reces-
sive. And in the second generation one-fourth of
the vines were short because the factors for short-
ness were segregated, according to the theory of
chances, and one-fourth of the vines were pure
recessives.

The fact of such dominance and recessiveness
between pairs of heritable characters is too ob-
vious to escape attention of any careful practical
experimenter, now that attention has been called

[220]

ON THE QUICK GROWING WALNUT

to it. But it is equally obvious that there are vast
numbers of other heritable characters regarding
which no such clear matching as to dominance and
recessiveness is observed to take place.

And so the early enthusiasts were led finally to
see that Mendelian dominance and recessiveness
apply only to a certain small number of hereditary
factors in the case of any individual plant or
animal.

They came presently, after much heated argu-
ment, to admit that dominance and recessiveness
constitute after all only a minor aspect of Men-
delian heredity.

Yet this aspect of the subject, even if not all-
important, has obvious interest. And the question
naturally arises as to which ones among the num-
berless hereditary factors in the case of any given
organism will "Mendelize" in this sense, and why
these factors will thus Mendelize while others fail
to do so.

The answer is found, apparently, in the simple
assumption that the factors that show the phenom-
ena of dominance and recessiveness are those that
are relatively new acquisitions in the germ plasms
of the species under observation. Traits that have
been the common heritage of the ancestry for un-
told generations, constituting the fundamental
structures of the organism, do not Mendelize. They

[221]

LUTHER BURBANK

have proved their merit, and are accepted as part
of the necessary equipment of the plant, not sub-
ject to the testing process that Mendelism essen-
tially constitutes.

Such fundamental structures are, for example,
the root and stem and leaves and stamens and pis-
tils of a flowering plant. As to their broad essen-
tials of form and structure, these fundamental
organs are inherited en bloc, and never jeopar-
dized by being weighed in the Mendelian scale.

But the newly acquired characteristics, such as
details of leaf form, or color of petals, or size and
quality of fruit — these are matters that are subject
to modification because they have not as yet estab-
lished themselves as fundamentally necessary in
any detail of form or color to the species. These
fall within the scope of Mendelian testing.

For hundreds of thousands of years, doubtless,
the progenitors of plants that now have flowers
were provided with roots and stems and leaves,
and with essential reproductive organs, but had no
blossoms. In comparatively recent times the blos-
soms were developed. And the modifications of
color of the blossoms in the case of any given
species are, as we have found reason to suppose,
of still more recent origin.

These modern details, then, and their like, are
the ones that are subject to variation and that are

[222]

ON THE QUICK GROWING WALNUT

still matter for change and adaptation; still in the
experimental stage, as it were. And precisely be-
cause such is their status, these are the things
that are subjected to the Mendelian test when they
are brought in juxtaposition, through hybridizing,
with forms that differ as to these details.

And as only the relatively new structures
Mendelize, so it is the newer member of any pair
that assumes prepotency or dominance. Contrari-
wise, the older member is recessive.

Students of different examples of Mendelian
heredity, as applied to animals and plants, have
puzzled long to discover the underlying principle
that determines which character shall be dominant
and which recessive. But this simple principle
appears to furnish the explanation.

The new trait or characteristic is dominant over
the older one precisely because it is new.

By making it dominant, nature gives it the best
possible chance. It will reproduce itself in all the
immediate progeny of the individual that possesses
it. Thus nature shows anew that she is progress-
ing. She accepts the new characteristic and gives
it more than an even chance.

But at the same time she is not so foolish as to
renounce the old character without full testing.
She allows it to be subordinated for a generation,
but in the next generation it reappears, isolated, to

[223]

The Royal Walnut in Winter

This is the same tree shown in the preceding picture,

photographed after it had shed its leaves. Observe the size of

the trunk, in comparison with the man's body, and the straightnett of

trunk, indicating a large quantity of lumber. The wood itself

has the good qualities of the black walnut, being hard and

durable, and susceptible of taking on a fine polish.

ON THE QUICK GROWING WALNUT

compete with the dominant character. And
whether in the end the new dominant character
will prove itself and prevail, or whether the re-
cessive character will re-establish itself, depends
entirely on the value for the species of one char-
acter as against the other.

Mendelian heredity, then, is a testing out
process for new characters. It is, as it were, the
skirmish-line of the advance guard of evolution.
So long as a character is subject to Mendelian
transmission, showing the phenomena of domi-
nance and recessiveness, it is a relatively new and
unfixed character still on trial.

And in proportion as any character has proved
itself and has passed the trial stage, it becomes
blended with the hereditary factors that have more
stable position, just as conscious acts of the indi-
vidual become instinctive or reflex when often
enough repeated.

In this view, then, the so-called unit characters
that Mendelize are, as was said before, merely the
fringe to the great fabric of heredity. They serve
the plant developer an admirable purpose, and,
indeed, it is with their manipulation that he is
chiefly concerned. Their relative insignificance is
evidenced in the fact that the plant developer
cannot possibly produce major modifications in
the organisms with which he deals.

[225]

LUTHER BURBANK

He does not attempt to make squash vines into
oak trees, or blackberry briers into tomatoes.

He recombines those newer, and hence less im-
portant, structures and qualities of which the fact
of their Mendelizing is adequate proof of their
newness and relative unimportance. If he would
get beyond this and create really new forms, add-
ing something to the plant that no ancestor of the
plant ever had, he could hope to do this only if a
term of life were granted him that would be meas-
ured not in mere years but in millenniums. For
evolution is a slow process, and the history of the
development of natural species is measured in
geological eras.

Selection and Mendelism

Perhaps it may be worth while to illustrate this
matter a little more in detail, that we may make
clear precisely what manner of thing the plant
developer is doing when he produces a new race
by selection.

We have stated over and over that the process
of hybridizing and the process of selection are
complimentary. One supplements the other. In
hybridizing we make possible new combinations of
the hereditary factors, and in selecting through
successive generations we isolate certain definite
combinations, and thus produce what we call new
varieties. Now it is frequently stated by the ex-

[226]

ON THE QUICK GROWING WALNUT

perimenters who have paid attention only to a few
conspicuous characters that Mendelize, that all
possible combinations of characters will occur
among the second generation hybrids, provided
only enough of these are produced.

Possibly this statement is correct. But it is not
susceptible of demonstration because it would not
be feasible to produce enough individuals in a
single generation to put it to the test. For the num-
ber of possible combinations increases in geo-
metrical ratio, as we have seen, with the increased
number of characters under consideration. And a
really penetrating view of the situation reveals to
us hereditary factors in the germ-plasm of each
individual plant that would be numbered, could
we isolate them, not merely by tens or scores; not
merely by hundreds or thousands; but rather by
hundreds of thousands or millions.

Such a statement probably will not surprise any
one who has read the various preceding chapters
in which we have viewed various aspects of her-
edity. But to those experimenters who have been
prone to think of "unit characters" as few in num-
ber, such a statement will perhaps seem anoma-
lous. Yet there can be no question that it is fully
justified.

In point of fact, what the present day student
of heredity usually speaks of as a unit character

[227]

LUTHER BURBANK

might better be referred to as a "unit complex,"
or by some allied term that would suggest its com-
plicated character. The word "gene-complex" has
been suggested in a similar connection.

It would appear that the real purpose of se-
lective breeding through many generations is to
remove one after another of the factors that dom-
inate or mask other factors, so that subordinate
or recessive factors may make themselves man-
ifest.

No one who has experimented widely will
doubt that it is possible by a series of selections
extending over several generations to accentuate a
given character, say to bring out the crinkled for-
mation of the poppy petal, or the corrugations in
the leaf of a wild geranium, or an added row of
petals in a balloon-flower. And it goes without say-
ing, that, according to the modern terminology, the
character thus isolated must be represented by an
hereditary factor which was present in each suc-
cessive generation utilized in our experiment, but
which for some reason was not enabled to make
its influence so potentially felt in earlier genera-
tions as it was in later ones.

And the only logical explanation appears to be
that in each successive generation of the plants
carefully selected and inbred, there was a new re-
distribution of factors, always along Mendelian

[228]

Another Fine Specimen of the Royal Walnut

This magnificent tree, one of the first seedlings of the

Royal walnut, stands in a dooryard beside the Sebastopol road,

near Santa Rosa. It bears mute but eloquent testimony to the success

of one of Mr. Burbank's early experiments in

hybridizing forest trees.

LUTHER BURBANK

lines, which isolated, in the case of the individual
we selected, the particular character which we had
under observation more and more completely.

Whereas, in a simple case of Mendelian her-
edity, where one pair of factors is in mind, there
is complete isolation of the recessive factor in one
case in four; in this complex case there is isolation
of groups of factors, and in one case among thou-
sands there may occur such relatively complete
isolation of the factors for quality we are seeking
as will serve our purpose. Such isolation might
occur in the second generation, but it cannot be
counted on to occur until we have tried again and
again, in each successive generation, using material
that is a little less complex because a certain num-
ber of disturbing factors have been segregated and
removed.

We may perhaps illustrate the meaning of all
this a little more clearly if we suggest that each
so-called unit character with which Mendelian her-
edity deals is in reality made up of a thousand
factors. I do not mean to imply that the number
is just that; it is merely that a thousand is a con-
venient round number for purposes of our com-
putation.

There would be, then, a thousand factors for
color combined to make up what we commonly
speak of as the unit factor for color; there would

[230]

ON THE QUICK GROWING WALNUT

be a thousand subordinate factors for form of
flower; a thousand others for texture of petal; a
thousand others for odor; yet another thousand for
hardiness; and so on for each and every patent
characteristic of flower and twig and stem and root
of the plant. In the aggregate, let us say, there are
a thousand different "unit characters," each made
up of a thousand minor factors, so that the total
number of hereditary factors stored in the germ-
plasm and fighting for recognition, in the case of
a single plant, is a round million.

Each of these million factors has been devel-
oped in the long slow process of evolution, one
after another added, generation by generation, or
era by era, beginning with the time when the
remote primordial progenitor of the plant was a
single-cell organism.

In the course of the ages, development has
taken place along divers lines, and it has come to
pass that certain combinations of hereditary fact-
ors have been grouped into systems that have so
long been working in harmony together that they
cannot be separated. The members of one such
group determine the architecture of the root; the
members of another group determine the archi-
tecture of the stem; and so on for each of the
patent characters.

But there are other groups of factors that are

[231]

Foliage and Fruit of the Royal Walnut

v.Zh?<L°l,iaae °L f£e easter* ^d western black walnuts is
to IV£ *\milar' and the foliage of the Royal hybrids maybesaid
£mi0nrofeSembla?Ce l° that of both »arents- ' i'irownintx.
LfhtET' however' « this Picture shows, in keeping
with the very great vigor and fecundity of the tree.

ON THE QUICK GROWING WALNUT

less ancient in their origin. There were some that
made their way into the germ plasm of the an-
cestors of the plant so recently as half a million
years ago. There are others that are more par-
venus of perhaps ten thousand years. And there
are yet others that are upstarts of literal yesterday.

Each one of these hereditary factors is striving
for recognition and endeavoring to make tangibly
manifest the condition or quality or form or con-
stitution of tissue that it specifically represents.

And, according to the view just presented, the
thousand factors that make up any given complex
stand in such sequential relation to each other that
each successive one controls in a measure its
predecessor in point of time, and is controlled by
its successor. The very newest factor that has been
admitted to the coalition has a more powerful
influence than any other single member of the
coalition.

But meantime this most powerful individual is
after all only one among a thousand.

In a company of a thousand men, some one
man is stronger than any other. But this strongest
individual would be infinitesimally week in com-
parison with the combined strength of the
other 999.

This is the important thing to bear in mind.
The newest member in each of the thousand or so

[233]

LUTHER BURBANK

hereditary "complexes" that we speak of as unit
characters is the most powerful individual factor.
But, inasmuch as the great body of antecedent
factors are using their influence in unison in
another direction, it is inconceivable that the in-
fluence of the single new factor should greatly
change the aggregate result.

In this view, what we term a species is a com-
pany of organisms in the germ plasm of which the
groups of factors for each main characteristic have
become purely and unqualifiedly recessive, so that
they act as a unit in producing a given character.
They thus determine the chief characteristics of
heredity in the Darwinian sense, which finds its
popular expression in the phrase "like produces
like.'*

Meantime, there are always minor groups of
newer characters that are fighting for recognition,
and while these are relatively insignificant because
of their newness and small number as compared
with the whole, yet they are conspicuous and im-
portant in the eyes of the plant developer because
they represent precisely those modifications of
form and constitution and color that mark what we
speak of as variations from type; and because they
are so matched against one another in heredity —
in the manner that we call Mendelian — as to make
it possible for the plant developer to segregate and

[234]

A Striking Contrast in Seedlings

Here are two seedling hybrid walnuts of the same age
grown from nuts of the same tree, and having had precisely
the same care. They are second-generation hybrids, hence the wide
variation in size and vigor of growth. One of these plants
will grow into a gigantic tree: the other will remain
dwarfed always. Obviously there are fine
opportunities for selection among
the seedlings of the hy-
brid walnuts.

LUTHER BURBANK

recombine them variously by hybridizing, and thus
to develop new races from the old stock.

When, however, the plant developer, through
his hybridizing experiments, brings together
groups of characters in which the old guards, so to
speak, that have control over the fundamental
characters are in conflict, no union is possible.

Either fertilization will not take place, or the
offspring will be sterile. Only within narrow lim-
its, and as regards the new and relatively unes-
sential characters, can there be diversity or, at
most, the accentuation of old characters.

Such an accentuation, for example, occurs, we
may suppose, in the case of the hybrid walnuts,
which take on gigantic growth. Both Persian wal-
nut and California walnut have in their germ
plasm the hereditary factors of large groups of
remote ancestors of the Mesozoic era, when gigant-
ism was the fashion, but these factors have for
long generations been subordinated by newer ones
born in a less favorable era. Now, however,
hybridzation brings the two strains together, and
the two dominant groups of factors for slow and
relatively dwarfed growth, in some way mask or
neutralize each other, enabling the earlier groups
to make their influence felt.

And here, as we have seen, the factors for
growth that have thus been rudely disturbed as to

[236]

ON THE QUICK GROWING WALNUT

their hitherto harmonious coalitions, are reassorted
in the second generation, as united groups acting
along Mendelian lines, so that part of the progeny
of the second generation are giants, and part of
them are dwarfs, and that all manner of inter-
mediate forms find recognition in the case of dif-
ferent individuals.

In no other way known to us could such a dis-
turbance of the coalitions of hereditary factors
have been brought about. So the plant developer
who thus brings together racial strains that have
been long separated introduces a disturbing ele-
ment that in its practical effects may produce such
modifications as could only be produced otherwise
through the aggregate influences of environment
for almost numberless generations.

But let it be repeated that even when the
hybridizer effects such a disturbance as this, he
can do no more than to enable subordinated her-
editary factors to make themselves manifest.

He is dealing with material that has been
brought together through age-long experiments,
and even though the new combinations that he
effects may be striking ones, he may rest assured
that even his most spectacular achievement is but
a feeble replica of plant developments with which
nature has experimented thousands of times over
in the course of the long evolutionary ages.

[237]

Tapping the Rubber Tree

This primitive method of tapping the rubber tree will

insure a large flow of sap, but will also endanger the life of the

tree itself. In the cultivated orchards, the rubber tree is tapped in a

more conservative manner, avoiding injury of the tree. But

of course the principle involved is everywhere the same.

Trees Whose Products

are

Useful Substances

From the Sugar Maple to the Turpentine Tree

EVERYONE who had the good fortune to be
born in New England and to live in the
country will treasure among the most
pleasant reminiscences of his boyhood the recol-
lection of his first visit to a "sugar bush."

The sweet sap drawn through a magic spigot
from a hole in the tree trunk; the boiling pot in
which the sap was transformed into the most
delectable of syrups; the transformation of the
syrup into a wax of quite matchless flavor by
pouring it on the snow — these are things that have
no counterpart. They must be experienced to be
appreciated, and no one who has experienced
them is likely to forget them.

To the unfortunate who has not been privileged
to visit a sugar bush, the product of the maple is
usually known only in its ultimate crystallized
form in which it constitutes a brownish sugar of

[Volume XI — Chapter VIII]

LUTHER BURBANK

characteristic and delectable flavor. And I regret
to say that many people who suppose themselves
familiar with this product know it only in a diluted
and adulterated form in which only a suggestion
remains of the real maple quality.

Nor does there seem to be much prospect of
improvement in this regard, for, so far as I know,
the maple tree is seldom or never cultivated for the
garnering of its unique crop. The relatively small
quantity of maple sugar that finds its way to the
market is the product of trees that chanced to grow
in the woodland and they are reserved not so much
as sugar producers but as ultimate material for
lumber. Yet maple sugar is a sweet of acknowl-
edged quality, and one that deserves a larger
measure of recognition as a commercial product
than has hitherto been given it.

Possibly the time may come when maple trees
will be set out and cultivated for the production
of sugar. But it is hardly likely that such cultiva-
tion of the maple can ever constitute a significant
industry, because the product of a single tree is
relatively insignificant.

It is only the fact that the sugar maple has wood
of such quality of fiber as to make it valuable for
the cabinetmaker that could justify the cultivation
of these trees as a commercial enterprise.

On the other hand the amateur orchardist

[240]

A Fir Tree

Just as the tropics have their gum producing plants, such

as the rubber tree, so do the temperate and arctic zones have

their gum producers in the flrs and pines and other evergreens. Tht

tree shown here is a fir which Mr. Burbank is observing by

reason of the quantity and quality of its exudate.

LUTHER BURBANK

might do far worse than to set a row of maples, as
ornamental trees about the borders of his orchard
or gardens, regarding the capacity of the tree to
produce a certain amount of sugar as an incidental
attraction that adds to the value of a tree that
otherwise is deserving because of its beauty of
form and general attractiveness.

The production of the sweet sap that has made
the sugar maple famous gives this particular
species exceptional interest among the members
of a very meritorious family. Just why this
species should have developed the capacity to
produce so sugary a sap in such abundance, it
would perhaps be difficult to say. A certain amount
of sap may be drawn from the tissues of other
maples, and even from the walnut and butternut,
and in diluted form from the birches; but only the
sugar maple produces sap of such quality as to be
of real value.

When the Sap Runs Best

And of course it is well known that the sugar
maple itself has a "flow" of sap that is worth tap-
ping, for a very brief period each season, just as
winter is merging into spring. It is traditional at
least among the makers of maple sugar that the
sap runs best in those days of early spring when
the sun shines brightly while there is a coverlet of
snow on the ground. At this time, all that is neces-

[242]

ON GUM AND SUGAR TREES

sary is to bore an auger hole in the trunk of the
tree, and insert a spigot or grooved stick to guide
the sap into a bucket.

A single tree may be tapped in several places,
and a bucket of sap will run from each spigot in
the course of the day.

The sap itself is a clear, watery fluid, the sweet
taste of which gives assurance of the quality of
the sugar it contains. By boiling the sap to evap-
orate the surplus water, a thick syrup is produced
which crystallizes on cooling, producing the maple
sugar of commerce.

Nothing is added to the sap and nothing but
part of its watery content is taken away from it —
that is to say, if it is honestly made. The sugar as
the maple supplies it, is a perfect product requir-
ing no diluent and calling for no elaborate process
of manufacture.

Perhaps it is not so much matter for surprise
that maple trees produce this sweet sap in such
abundance as that other trees do not more gener-
ally imitate its example. For the function of the
sugar in supplying nourishment for the young buds
before the leaves are sufficiently expanded to begin
their work of sugar manufacture is clearly enough
understood. All other deciduous trees must supply
nutriment in similar way to their growing buds.

But in the case of other trees, either the sap

[243]

A Spruce Tree

The spruce is one of the most familiar and most highly
prized of evergreens in many of our northern forests. Its res-
inous exudate was formerly very popular as a commercial product
known as "spruce gum." Nowadays the demand for chew-
ing gum has so increased that it has been necessary
to find other materials for its manufacture,
and the once-familiar spruce gum
has practically disappeared
from the market.

ON GUM AND SUGAR TREES

will not flow in abundance or it is of such quality
as to have no value.

The manner of production of the sap may
be more or less accurately inferred from what we
have already learned of plant physiology. We
know that the leaves of the tree metamorphose
water and carbon into sugary substances which in
turn are transferred to various parts of the plant
to be stored, usually in the form of starch. In the
case of the maple, we may assume that the carbo-
hydrates, as they are manufactured in the leaf-
laboratories, are transferred in the current of sap
that flows downward from the leaves through
branches and trunk as a countercurrent in the
cambium until it finally finds its way to the roots
of the tree and is there stored for the winter.

When spring comes and it is time for the new
leaf buds to put forth, the supplies of nourishment
are retransformed into soluble sugars, dissolved in
the water that is taken in by the rootlets, and trans-
ferred from cell to cell and along the little canals
in the wood under the cambium layer of the bark,
until they reach the twigs where the leaf buds they
are to nourish are located.

It is doubtless the so-called "root pressure"
(which we have been led to interpret as due to
osmosis) forcing the sap upward that causes it to
flow from the wound in the tree made by the

[245]

LUTHER BURBANK

auger. To what extent the interference with the
supply of nourishment that was being convoyed to
the buds retards their development, might be inter-
esting matter for observation.

But this is something that does not greatly con-
cern the sugar maker, and to which he doubtless
never gives a thought.

It is also interesting to conjecture whether it
might be possible by selective breeding to produce
a variety of sugar maple that will furnish sap in
exceptional quantity and of unusual quality. The
case is obviously different from that of the sugar
prune or the sugar beet, both of which have been
trained to increase their sugar content.

But there is no doubt that different individual
sugar maples differ widely in their sap producing,
or at least in their sap rendering, quality. Pre-
sumably the difference may be due to the size of
the root system. But so far as I know there are
no accurate observations on the subject, nor has
anything been done to determine whether a better
race of sugar maples could be developed.
Other Plant Juices

The extraordinary plant laboratories that man-
ufacture sugars out of water and air is capable of
transforming these sugars into many unusual sub-
stances, differing in character with the constitution
of the particular plant.

[246]

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LUTHER BURBANK

There are certain classes of juicy exudates,
however, which appear to have characteristics that
make them useful to plants of many types. Promi-
nent among these are the milky juices that when
dried constitute rubber, and the resinous ones that
constitute tars and resins and turpentine.

Nothing could be physically much more dis-
similar than a piece of rubber and a teaspoonful of
oil of turpentine.

But the chemist tells us that each of these sub-
stances is composed exclusively of the two ele-
ments carbon and hydrogen; the only difference
being that the turpentine molecule has 10 atoms of
carbon and 16 of hydrogen, whereas the molecule
of rubber has 8 carbon atoms and 7 atoms of
hydrogen.

Just how the elements are compounded, and
just why they should make up substances of such
unique characteristics when brought together in
these particular proportions, even the chemist does
not know. Nor, until recently, was he able to dupli-
cate the feat of building up these complex mole-
cules, even though he is perfectly familiar with the
general properties of the atoms of both carbon
and hydrogen.

In very recent years, however, chemists have
been at work on the problem of compounding the
atoms in such a way as to get them together in the

[248]

ON GUM AND SUGAR TREES

right combination to produce organic substances.
And, although this work is only at its beginning, a
good measure of success has been attained.

In particular, the chemists of Germany and
England have recently succeeded in combining
carbon and hydrogen in the proportion of 8 atoms
of the former to 7 of the latter and thus have
produced an artificial rubber that is not merely
an imitation rubber but is as truly pure rubber as
if it had been produced in the cellular system of
a plant.

Indeed, the artificial product may be said to be
somewhat more pure than the natural, inasmuch
as the latter is more or less contaminated by ex-
traneous products.

Reference has elsewhere been made to the
familiar feat of the chemist through which the
famous dyestuffs, indigo and madder, have been
manufactured in the laboratory, and manufac-
tured so cheaply as to compete successfully with
the natural product of the indigo and madder
plants. What was a large plant industry only a
few years ago has thus ceased to have importance.
The indigo plant is still cultivated in the east, but
the entire industry has been changed by the dis-
coveries of the chemist.

Only a few years ago a plant known as the tar
weed (Madia), to which we have had occasion to

[249]

Turpentine Trees

There are many of the evergreens that produce resinous

exudates allied to turpentine. But the trees that produce the

chief supply of turpentine of commerce are the sea pine, the Scotch

fir, the Norway pine, and the Corsican pine in Europe, and the

swamp pine and the so-called loblolly in the United

States. The swamps of North and South Carolina

and Georgia are the chief source of supply of

commercial turpentine in this country.

ON GUM AND SUGAR TREES

refer in another connection, was gathered and its
juices extracted for the making of the pigment
madder. But it would not pay to undertake this
work now, since the chemist has learned how to
make madder from coal tar and hence has substi-
tuted for a plant industry an enterprise associated
with the manufacture of gas.

It will doubtless be a long time before the
manufacture of artificial rubber makes corre-
sponding encroachments on the industry of manu-
facturing rubber from the plant juices. Still it is
quite within the possibilities that this may come
to pass in the course of the coming generation.

In the meantime, the rubber industry is a vastly
important one, and the principal trees that supply
the juices that on evaporating constitute rubber
are cultivated in vast plantations in various trop-
ical regions. Moreover rubber is gathered from
wild trees of several species, although in recent
years the cultivated trees have largely been de-
pended upon to meet the growing needs of the
industry.

Trees of the genus Hevea are the most import-
ant source of rubber. But there are many other
trees, the juices of which contain the essential con-
stituents of rubber in the right combination, and a
good many of these have commercial possibilities.

I have referred in another connection to my

[251]

LUTHER BURBANK

experiments with tropical plants of the genus
Asclepias, relatives of the familiar milkweed.

I have undertaken tentative experiments to dis-
cover whether these plants might be developed to
a stage that would make them commercially valu-
able as producers of rubber. The recent discov-
eries of the chemist make experiments in this line
somewhat less valuable than they hitherto seemed.
Yet the demand for rubber is so great, in these
days of electricity and automobiles, that there
seems little danger of overstocking the market.
And if a plant could be developed that could be
grown in temperate regions, and they would pro-
duce the rubber-forming juices in adequate quan-
tity, such a plant would constitute a very valuable
acquisition for a long time to come, even should
natural rubber ultimately be supplanted by the
laboratory product.

The method of gathering the so-called latex, or
milky juice, which is virtually rubber in solution,
is curiously similar to the method of obtaining the
sap of the sugar maple. Indeed the latex may be
drawn in precisely the same way, by boring a hole
in the trunk of the rubber tree and inserting a
grooved stick along which the juice will run into
a receptacle. But the cultivators are not usually
content with so slow a method, and there are
various methods of tapping the tree that expose a

[252]

Balsam Fir Tree

This tree produces a resinous exudate that is peculiarly
clear and transparent, and is known in commerce as Canada
balsam. This transparent gum is highly prized by microscopists for
the embedding of miscroscopic sections and speci-
mens of various kinds.

LUTHER BURBANK

larger surface of the cambium layer and thus
extract the milky juices in larger quantity.

In the case of the wild trees it is not unusual
for the natives of Mexico, Central America, and
South America to make a series of "V" shaped in-
cisions in the bark of the tree, placing a receptacle
at the point of each "V" and thus securing a rela-
tively enormous amount of fluid regardless of the
fact that they jeopardize the life of the tree itself.

Of course cultivated groves or plantations are
tapped in a more conservative way, but the prin-
ciple involved is everywhere the same.

The latex of the rubber tree is comparable to
the sugary sap of the maple. It appears to be a
mere accident that this juice has the property of
coagulating to form the substance called rubber
which we now find so important. But this sub-
stance, obviously, as man uses it, has small place
in the economy of the plant. Coagulated latex
would serve no better purpose in the tissues of the
rubber tree than would coagulated blood in the
veins of a human being.

Oils and Resins

Of course the latex of the rubber tree might
exude when the tree received an accidental
injury, as from a falling limb, and in such case it
would be advantageous to the tree to have the
juice coagulate, just as coagulated blood is useful

[254]

ON GUM AND SUGAR TREES

to a wounded man. In each case coagulation
prevents excessive hemorrhage.

Possibly this may explain the quality of the
latex, its capacity to coagulate having been devel-
oped through natural selection. But under nor-
mal conditions, at least, the latex is always fluid,
and its properties are little more like those of
rubber than are the properties of the maple tree
like those of sugar.

Of course the same thing is true of the plant
juices that when dried or partially evaporated
constitute the various gums and resins. As manu-
factured in the tree they are transformed sugar
products, and they are always in solution. Only
when the juices are exposed to the air, as when
they exude from an injured surface, do they coagu-
late to form the gummy or resinous substances
that become articles of commerce.

In some cases the exudate may be separated
into two or more commercial constituents. Such
is the case with the juice of those trees that pro-
duce turpentine. The liquid that flows from the
tree, corresponding to the sap of the maple and
the latex of the rubber tree, may be evaporated
or distilled in such a way as to be changed in part
to a solid gummy or even vitreous substance, and
in part to the somewhat volatile fluid familiar as
turpentine.

[255]

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ON GUM AND SUGAR TREES

Turpentine, unlike rubber, was known to the
ancients, and was an extensive article of commerce
in classical times. The original tree from which it
was obtained is known as the terrebinth tree. It
is a native of the islands and shores of the
Mediterranean and western Asia.

There are many trees, however, the sap of
which has this resinous property, including most
members of the family of conifers. The principal
supply of crude oil, or common turpentine, in
Europe, is obtained from the so-called sea pine,
grown largely in France. The Scotch fir, the Nor-
way pine, and the Corsican pine are other sources.
In the United States the swamp pine and the so-
called loblolly trees that grow in the swamps of
North and South Carolina and Georgia, are the
chief source of the commercial turpentines,
although various other species are more or less
utilized.

A turpentine of peculiar quality that is highly
prized for some industrial purposes is obtained
from the balsam fir (Abies Balsamae), and is
known as Canada balsam.

Hitherto, the producers of turpentine have been
found in the wild state, and no one, probably, has
given a thought to the possibility of developing
races of pines that produce an exceptional quan-
tity of the resin- and turpentine-forming juices.

[257]

LUTHER BURBANK

But with the modern tendency to apply scientific
methods to forestration in general, doubtless the
question will ultimately arise as to whether the
turpentine trees may not be improved along With
the timber producers.

That trees of the same species differ quite
radically in the amount of the valuable juices is
certain, so there would appear to be no reason
why it may not be possible to develop varieties of
trees that will be conspicuous for this quality, just
as other trees have been improved as to their
powers of growth or their capacity to produce
abundant crops of fruit.

Varied Products of the Plant Laboratory

An incidental use of the resinous exudate of
the pine tree that has come to assume considerable
economic importance is the production of chewing
gum.

The habit of gum chewing appears to have
originated or at least to have gained chief popu-
larity in America in comparatively recent times.
The resin that exudes from the spruce was the
substance that was chiefly used, under the name of
spruce gum, until somewhat recently. But of late
years the chewing gum industry has reached pro-
portions that make it impossible to meet the
demand from this source. And it has been found
that ordinary resin, combined with sugar and lin-

[2581

A "Weeping" Birch

This beautiful tree stands beside Mr. Burbank's cottage

on his experiment farm at Sebastopol. The birches are very

hardy trees, and they merit a place in every park and garden; those

with white bark in particular furnishing a striking and

picturesque contrast to other forms of shrubbery.

LUTHER BURBANK

seed oil, with some flavoring added, serves the
purpose of the original spruce gum so the latter is
now seldom seen in the market. More recently
chicle, a gummy substance which exudes from
several tropical trees, has been imported in great
quantities, and is now supplanting all other sources
of gum.

The supplying of turpentine and its products
gives the conifers high range among trees that
produce commercial by-products of great import-
ance. But with the exception of the pines, the
trees that produce really important exudates or
oils or chemicals are indigenous to the tropics, or
at least are confined to the warm temperate zone.
I have thought many times in recent years that I
should like to have a plant laboratory in the
tropics for the testing of tropical plants as to the
production of useful commercial products, and for
the development of improved varieties of plants
the products of which are already utilized.

It would be worth while, for example, to make
very extensive experiments by way of testing the
qualities of the different trees that deposit in their
bark the bitter compound known as alkaloids, a
galaxy of which are prized for their medicinal
properties. These are very complex combinations
of carbon, hydrogen, oxygen and nitrogen. That
is to say, they have the same constituents as proto-

[260]

ON GUM AND SUGAR TREES

plasm itself and they differ from the gum and
resins that we have just been considering in that
each molecule contains at least one atom of
nitrogen.

The sugars, it will be recalled, occupy an inter-
mediate place, inasmuch as they, unlike the resins
and rubber, contain oxygen; but they contain no
nitrogen. The formulae given by the chemist for
the different alkaloids are intricate but they differ
from one another only in the matter of a few more
or a few less atoms of one or another of the four
constituents of1 which they are all made up.

There is, for example, only the difference of
one atom of carbon and of four atoms of hydrogen
between a molecule of quinine and a molecule of
strychnine. Considering that the molecules com-
prise in the aggregate not far from fifty atoms, in
each case, this discrepancy seems trifling. That
the two drugs should have such utterly different
effects upon the human system is a mystery that
will be solved only when a much fuller knowledge
is gained as to the physiological processes than
anyone has at present.

But the plant developer, of course, has no con-
cern with this aspect of the subject. What inter-
ests him is the knowledge that different races of
cinchona trees, for example, are known to vary
greatly as to the proportion of commercial alka-

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ON GUM AND SUGAR TREES

loid deposited in their bark. And doubtless the
same thing is true of most or all other producers
of commercial alkaloids.

Seemingly there is a splendid field, then, for the
plant experimenter, could he establish a labora-
tory and experiment garden in the tropics, in the
development of improved races of cinchona trees
and of numerous other suppliers of medicinal
alkaloids. The monetary return from such an
enterprise would probably be larger than that
which usually rewards the efforts of the plant
developer in temperate zones, because the field is
virgin, and because there is no present possibility
of competition outside the tropics.

It remains to be said that there are a few other
trees and shrubs of our own latitude that may
advantageously command the attention of the
plant developer for the improvement of quantity
or quality of the by-products of their life activities
that man has found useful.

It seems not unlikely that the horse chestnut,
or buckeye, could be so educated as to become a
profitable starch producer. At present this tree
produces an abundant crop of nuts, but these are
worthless because they contain a bitter principle
that makes them inedible. Yet the nut of the horse
chestnut is very starchy and if the bitter principle
could be eliminated there is no reason why it

[263]

LUTHER BURBANK

should not prove both wholesome and nutritious.
The West Indians sometimes grind the nuts to
make meal. When this is soaked in water the
poisonous principle is partially removed, and the
residue is cooked and eaten.

I have experimented somewhat in the attempt
to test the western buckeye as to its possibilities of
improvement. As long ago as 1877, I began work
on this tree, and continued the experiments in a
small way for a number of years. I observed that
there was great variation as to productiveness of
trees, as to size of nuts, and also as to bitterness
of the nuts themselves.

I am convinced that it would be possible to
develop a variety in which the bitter principle
would be greatly reduced in amount and perhaps
altogether eliminated, and that at the same time a
nut having a high starch content could be
developed.

It has been found possible with the South
American plant called the casaba to utilize roots
that contain a poisonous principle for the produc-
tion of so important a commercial product as
tapioca. It is not unlikely that the nuts of the
horse chestnut, if developed until it had a still
higher starch content, could be utilized in some-
what the same way, even though the bitter prin-
ciple was not entirely eliminated.

[264]

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LUTHER BURBANK

There are some members of the laurel family,
also, that produce commercial products that make
them perhaps worthy of attention. The camphor
tree is too tender to be grown in our latitudes, but
its relative, the sassafras, is a common tree
throughout the eastern states, thriving even in
New York and New England. Its bark furnishes
the characteristic flavoring that is used for per-
fuming soaps and for similar purposes. The pro-
duction of the sassafras would not constitute a
significant industry under any circumstances,
doubtless, yet there would be a measure of scien-
tific interest in testing its capacities for improve-
ment, and not unlikely new uses would be found
for its product if it were made available in larger
quantity.

Another tribe that furnishes a product of a
unique quality is that represented by a familiar
wild shrub known in the eastern states as the wax
berry or candle berry (Myrica cerifera) and some-
times also spoken of as the bay berry owing to the
fragrance of its leaves.

This shrub bears an abundance of small berries
from which may be extracted a quantity of hard
greenish fragrant wax, which was formerly much
prized for the making of candles, and which has a
certain value for the various other uses to which
wax is put.

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LUTHER BURBANK

A good many years ago while traveling in the
east I found a candle berry bush that was of com-
pact growth and that produced a large crop of
waxy berries. I collected seed and brought it to
California, and for several years worked on the
shrub until, by selection, I had developed a variety
that produced at least ten times as many berries
and ten times as much wax as the average wild
plant. At the same time I experimented with a
Japanese member of the genus known as M. nagi
or M. rubra, and also with the California species
which is a tree growing fifty or sixty feet in height.

I endeavored to cross the three Myricas in the
hope of producing new varieties of value, but did
not succeed, no doubt because the attempt was not
carried out with sufficient pertinacity. The Cali-
fornia species produces a wax of much darker
color than the eastern one, but of about the same
degree of hardiness. I still have several fine blocks
of wax that were produced from these shrubs and
trees during the time of the experiment. Although
not successful in hybridizing the different candle
berry shrubs, the experiments were carried far
enough to show the possibility of great improve-
ment by mere selection. If there were a market
for the wax, the plant might be well worth
improving.

Even as it was, I advertised my improved

[268]

ON GUM AND SUGAR TREES

variety of candle berry, but as no one cared to buy
it, it was finally destroyed to make room for other
shrubs. This is another case in which a product
of intrinsic value has failed to find a market,
largely, no doubt, because the plant that produces
it has hitherto not been brought under cultivation,
and hence has not produced a sufficient crop to
bring it to the attention of the public and to create
a market.

It would not be surprising, however, if the
candle berry should be thought valuable enough in
future for development and cultivation on an
extensive scale. For the wax that it produces is
of unique quality, and it is almost certain to be
found of value in connection with some commer-
cial industry.

— Seemingly, there is a splendid
field for the plant experi-
menter, could he establish a
laboratory and experiment gar-
den in the tropics for the
development of improved pro-
ducers of medicinal alkaloids.

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Trees and Shrubs for
Shade and Ornament

Some Miscellaneous Tree Experiments

OUBTLESS the most interesting tree in the
world is the Sequoia. The mere fact that
this is the most gigantic of all existing
trees gives it distinction. But it has added interest
because it represents a link with the remote past.
Of course it might be said that any existing
vegetable represents a link with the past, since
every race has its lines of ancestry tracing back
to primordial times. But the Sequoia represents
the past in a somewhat different sense, inasmuch
as it has maintained more fixedly the traits of its
remote ancestors than has been done by any other
tree, probably, that now grows in the northern
hemisphere, with the possible exception of the
tulip tree, which represents a quite different type
of vegetation.

The story of the Sequoia's fight for life during
the remote geological ages when the climate of the

[Volume XI — Chapter IX]

LUTHER BURBANK

northern hemisphere was changing, has been out-
lined in an earlier chapter. Could we know the
details of the story, we should doubtless find that
the ancestors of the Sequoia migrated southward
before the chilling blasts of successive glacial
epochs, and made their way northward again in
the intervening periods. And of course the present
age may represent merely another of these inter-
glacial epochs, during which the Sequoia has
carried its return march along the coast to about
the fortieth parallel of latitude. It maintains in
this location its proud position as the one cham-
pion of the ancient traditions. And perhaps it will
still maintain them in some remote epoch of the
future when another ice age has driven man from
the northern hemisphere and reduced the civiliza-
tion of the twentieth century to a half-forgotten
tradition.

Be that as it may, the Sequoia and its daughter,
the redwood, stand to-day as sister giants in an
age of pigmies. Individual trees that are still
young according to the reckoning of their tribe
were gigantic centurions according to human esti-
mates when Columbus discovered America.

And Sequoias that are moderately old have
witnessed the ceaseless change of the seasons since
the period, perhaps, when Moor and Christian
were battling for supremacy in Europe in the dark

[272]

An Ivy-Clad Tree

Here is a tree fairly encompassed in a draping of English
ivy. The effect, to the human eye, is decorative and pleasing
as well as anomalous: but the tree must suffer somewhat in pro-
portion as the vine thrives.

LUTHER BURBANK

age that preceded the segregation of the modern
nations of Europe. The patriarchs of the race
were living in the days that saw the building of
the Egyptian pyramids.

A tree with such racial traditions and with such
individual representatives is surely entitled to be
considered the most interesting tree in the world.

Whoever has camped in a primeval forest of
Sequoias or redwoods will attest that merely to
enter into the presence of these colossal antedi-
luvians is to experience an almost overwhelming
sense of their grandeur. And it is the common
experience that this feeling of awe grows day by
day and becomes overpowering if you linger like
a lost pigmy in the shadow of the giants.

From our present standpoint the interest in the
Sequoias hinges on the possibility of growing seed-
lings or transplanting saplings for ornamental pur-
poses in the parks and fields. It is rather strange
that the attempt to do this has not been carried out
more extensively. Curiously enough, the redwoods
are grown more in England than they are any-
where in America outside the regions where they
are indigenous. But doubtless the climatic condi-
tions account for this. The trees thrive fairly well
in the relatively mild climate of England, but they
find the winters of the North Central and the
Northeastern United States prohibitive.

[274]

A "Pepperwood Tree" in Bloom

The photograph suggests the attractive quality of this tree

in blossoming time. At other seasons also it is an ornamental

tree of value, in regions where it will grow. Unfortunately it lacks

hardiness, and is not adapted to the climate of our eastern states.

LUTHER BURBANK

A tree that has weathered successive ice ages
should not mind the winters of the present era,
even at the northern boundaries of the United
States, one might suppose. But such an inference
misses the chief point of the Sequoia's ancestral
story. In point of fact, the giant trees are alive to-
day in something like their pristine form because
they migrated before the ice sheets and finally
found a place of refuge west of the Sierras where
they were sheltered from the northern blasts and
given protection by the tempered breezes of the
Pacific. As compared with the other conifers —
pines, spruces, hemlocks, cedars, and the rest — the
Sequoias are really tender trees. They are hardy
indeed in contrast with their ancestors of still re-
moter geological times. But they have never devel-
oped that extreme hardiness that characterizes
their modified and stunted cousins.

Nevertheless it has been found possible to raise
the Sequoia gigantia as far north as Central New
York. But the tree does not really thrive in regions
so inhospitable, and the redwood is even more
tender. In central and south-central regions of
the United States, however, the giant trees can be
grown to better advantage, and here they should
find a place as ornamental trees that has not hith-
erto been accorded them.

In the region of Washington, D. C, the Sequoia

[276]

ON ORNAMENTAL TREES

has proved altogether hardy, and of course it may
be grown readily anywhere along the Atlantic
Coast south of this region. It is a tree of extremely
rapid growth, almost equalling the eucalyptus. The
redwood also is of such rapid growth under culti-
vation that it soon overshadows most other trees.
Indeed, it grows so rapidly and requires so much
room that it is hardly adapted to use as an orna-
mental tree except in large grounds.

I have raised the giant Sequoia (it is known
technically as Sequoia gigantia) in the nursery
from seed, and the redwood (Sequoia semper-
virens) from cuttings as well as from seed. The
cuttings do fairly well if started in the fall and
treated like cuttings of other conifers.

As to the matter of selection and development,
the redwood itself may probably be regarded as a
comparatively recent variation from the form of
the giant Sequoia. The ancestors of the redwood
took up their location in the valleys nearer the
ocean and were modified until they are consid-
ered to rank as distinct species. But the similarity
of the two forms is obvious, and the two species
stand in a class by themselves — obviously allied
to other conifers in the form of leaf and cone and
manner of growth, yet so far outranking all others
as to be properly thought of as representatives of
a unique order of vegetation.

[277]

South American Yew Tree

This thrifty and symmetrical seedling, with erect stentfapJ*
and handsome foliage, is a visitor from the tropics, believed to^ ^y QW*
be a yew, growing in Mr. Burbank's grounds for observation and de-
velopment. It hus obvious qualities of attract&e- p*-
ness as an ornamental shrub. ^» V»

ON ORNAMENTAL TREES

Whether further modifications in the giant
trees could be wrought by hybridizing the two
forms or by selection among variant seedlings is
a question of interest.

Presumably, such modifications could be
brought about were there time for it. But in
dealing with a tree that is a mere child when it
has outlived half a dozen generations of men, the
plant developer feels himself in the presence of
forces that lie almost beyond his ken.

Moreover the attempt to deal experimentally
with the redwood is made difficult by the fact that
the tree seldom bears seed. Some of the woodmen
claim that it bears once in seven years, but this is
doubtless a mere guess, instigated by the popular
superstition connected with the number seven. On
one occasion, some thirty years ago, I was in-
formed that the redwoods were loaded with seed.
I went out with some helpers and gathered a dozen
grain sacks or more of the cones, which could be
obtained in any desired quantity. On drying the
cones I found that the seeds themselves made up
half the total weight.

There was a good deal of variation in the cones
themselves and in the seed from different trees.

The seed when dried kept its germinating
quality for seven or eight years. But only a very
small proportion of the seeds will germinate under

[279]

LUTHER BURBANK

any circumstances, even when fresh. This seems
to be especially true of seeds collected from the
younger trees — a fact that accentuates the already
sufficient difficulties that confront the plant devel-
oper who cares to undertake the rather discour-
aging task of experimental breeding with these
antique giants.

Nevertheless, it should be recorded that a cer-
tain amount of work has been done with the red-
wood, particularly in the way of selecting trees
that bear weeping branches. It has been observed
that seedlings usually show the characteristic
drooping branches of the parent form. In my
experience there is less variation among seedlings
of this type than among the normal ones. The
latter show a rather wide range of variation of
foliage, particularly where seed from different
localities is sown. Some are much lighter in color
than others, and there are various interesting char-
acteristics that may be noted by a close observer,
leaving no doubt that there is sufficient material
for the purposes of the plant developer.

Doubtless anyone who has patience to under-
take the task will be able to produce various types
of redwoods that will reveal interesting character-
istics of the remote racial strains that now are so
blended in the existing representatives of the
family as to be scarcely observable.

[280]

Japanese Magnolias

The magnolias have distinction among ornamental shrabs
because of their large and beautiful flowers, supplementing their
attractive foliage. There is good opportunity for hybridizing experi-
ments, utilizing the species from various parts of the world.
Here is a Japanese variety that will be used in such
experiments, by combining its strains with those
of the familiar American species.

LUTHER BURBANK

I must not attempt to speak except in a general
way of the other members of the great tribe of
conifers, the merits of most of which, as orna-
mental trees, are familiar to every garden and
landscape architect.

There are some scores of genera and some
hundreds of species of conifers but the varieties
are too numerous and too intricately blended for
accurate computation.

No other single region has so many forms of
evergreens, and ones that show such wide range
of variation, as the Pacific Coast region. It has
been estimated, indeed, that there are as many
species of conifers in California as in all the rest
of the world.

But the conifers of one kind and another grow
everywhere throughout the colder regions of the
northern hemisphere, some of them making their
way also to parts of the South.

Every one of them is an object lesson in the
possibility of plant variation; for as a class they
represent a modification of leaf form of the most
striking character to meet the exigencies of a
changing environment.

Time was, doubtless, when the ancestors of
the conifers had flat, spreading leaves like the
leaves of other forms of vegetation. But when the
climatic conditions changed, the pampering influ-

[282]

An Acacia Tree in Bloom

There are several species of acacias, introduced into Cali-
fornia from the southern hemisphere, that have become very
popular. Their value as ornamental trees is well suggested bu this
photograph. Unfortunately they are not as hardy as could
be desired, although they thrive almost everywhere
in California. African species of acacia
yield the gum-Arabic of commerce.

LUTHER BURBANK

ences of warmth and moisture being supplanted
by the chill and drought that presaged the onset
of perpetual winter, a premium was put on the
conservation of plant energies. Whereas before
the elements favored the tree that could raise its
head highest and thrust out the most luxuriant
growth of spreading leaves to absorb the carbon
from the heavily laden atmosphere, the time now
came when the tree that had a smaller system of
branches to nourish and a less expansive leaf
system had better chance of maintaining existence.

So in the lapse of ages, the conditions becoming
more and more hard, the trees that varied in the
direction of smaller size and narrower leaves had
an ever-increasing advantage. These survived
where their more rank-growing and luxuriant-
leaved fellows perished.

Thus generation after generation natural selec-
tion operated to modify the size of the trees and
to develop a race of trees with narrow leaves,
which ultimately were reduced to the form of
needles.

Such leaves, ottering the largest possible sur-
face in proportion to their bulk, could gain nour-
ishment from an impoverished atmosphere, and
at the same time would obstruct the rays of the
sun but little, so that the entire foliage of the tree
might secure a share of the all-essential light

[284]

The California Chinquapin as an Ornamental

Tree

This beautiful specimen of the wild California chinquapin
grows in Mr. Burbank's grounds at Sebastopol. Us flowers have
been used extensively in hybridizing experiments in the course of Mr.
Burbank's development of the hybrid chestnuts elsewhere de-
scribed in this volume. But the chinquapin tree has
obvious merits of its own as an ornamental
shrub, as this picture clearly testifies.

LUTHER BURBANK

which now, age on age, became less and less bright
as the earth changed the direction of its axis.

Of course there were other trees that did not
undergo this modification. But these were forced
either to make more rapid migrations to the south
or to give up the fight altogether and to submit to
extermination. The only ones that were able to
maintain existence in the regions where the cli-
mate became exceedingly cold were those that had
developed the new type of leaf-form, and had
learned to conserve their energies to the last
degree.

But of course the trees that took on this new
habit varied among themselves, and as they spread
to different regions such variations were developed
and fixed under the influence of different environ-
ments, until many tribes of needle-leaved trees
were developed so differently as to constitute the
races that the modern botanist terms pine and
spruce and cypress and juniper and hemlock and
yew and cedar.

Representatives of all the chief genera of coni-
fers have recognized a place among ornamental
trees and are everywhere popular in cold climates.
The variations among the different species are so
obvious as to attract the attention of the least
observant. And the opportunity to develop any
fixed new form is correspondingly good.

[286]

The Box Elder

Although popularly known everywhere as an elder, this is
really a maple, listed by the botanist as the ash-leaved maple
(Acer negundo). It is a hardy tree of rapid growth, much prized for
planting in semi-arid regions. There are several varieties, giv-
ing opportunity for experiments in selective breeding.

LUTHER BURBANK

I have raised large numbers of conifers of
many species, and have experimented with them
in the way of selection, producing in some cases
varieties of considerable interest.

I have, for example, developed several beauti-
ful varieties of the spruce, including some very
conspicuous forms with weeping foliage; also some
that grew very compactly, being strikingly differ-
ent in appearance from the usual spruce with its
long, graceful branches.

Variations in the color of foliage have also been
given attention, especially in the case of the Colo-
rado yew cypress (Abies nordmanniana) . I have
observed variations from budding sprouts in the
case of this cypress that were of interest. In par-
ticular I have seen a branch in a wild species (a
bud sport) that would droop several feet below
the other branches. Such a branch may generally
be propagated by grafting or from cuttings, and a
race of trees having this habit may thus be devel-
oped. There are corresponding variations in
cypress and other conifers grown from the seed.

The Douglas Spruce is a common California
form that is quite variable, and in this also the
variations sometimes appear as bud sports. The
Douglas Spruce has exceptional interest, because
it is a tree of very rapid growth. In many cases
where a tract of land has been burned over or the

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LUTHER BURBANK

trees have been cut off, there will spring up what
at first appears to be a growth of oaks alone. But
in fifteen or twenty years the growth of Douglas
Spruce will entirely overshadow the oaks, ulti-
mately kiling them off altogether, and presenting
yet another illustration of the practical operation
of natural selection.

But there is very great variation among the
different species of conifers as to rapidity of
growth. So there is fine opportunity for the experi-
menter to select the more rapid-growing trees, and
thus to develop a race of timber trees of excep-
tional value.

The experiment is not difficult because the
Douglas Spruce bears seed while quite young, par-
ticularly when the trees stand by themselves. The
seed remains in the cones for some time, to mature,
so that it may be collected at any season of the
year. The seeds germinate readily, the seedlings
may be easily transplanted, and in general this is
one of the easiest conifers with which to work.
The hardiness of the tree and its adaptation to all
soils and climates are further merits that com-
mend it to the attention of the plant developer,
whether he have in mind a tree for ornament or
for reforestration.

The experimenter should know, however, that
the seed of the spruce, unlike that of the redwood

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and some other conifers, retains its vitality for a
short time only. If attention is given to the secur-
ing, of fresh seed, the experiments can scarcely fail
to go forward successfully.

There are, of course, almost numberless other
species and varieties of conifers that hold out
inviting opportunities for the plant developer. A
beginning may be made with almost any varieties
that chance to grow in your dooryard, and the
facility with which the different varieties may be
reproduced, together with the wide range of varia-
tion, offer opportunity for selection and insure
interesting developments, provided you have
patience to wait for them.

Some Deciduous Favorites

But if there are no broad-leaved trees that
quite equal the hardiest of the conifers in capacity
to withstand cold and to draw nourishment from
rocky soils under disheartening conditions, there
are a few tribes of deciduous trees that make at
least a commendable effort to rival them.

Notable among these is the birch. But the
beech and oak and maple and hickory and walnut
also have representatives that are able to with-
stand the winter in regions where the mercury
freezes.

All of these have a certain importance as orna-
mental trees, but in the main they are valued

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LUTHER BURBANK

rather for their timber, and we have dealt with
them when we spoke of forest trees.

There is a considerable company of trees of less
hardy character that nevertheless are resistant
enough to thrive in the streets, parks and gardens
of our northern States if given a certain amount of
protection, even though some of them could not
make their way in the wilds in competition with
the hardy tribes just mentioned.

These trees are less hardy than the others,
presumably because they migrated a little more
rapidly in the old days of changing climates, and
kept far enough away from the ice sheet to be able
to retain something of their taste for tropical con-
ditions. They not only retained the broad leaf
system, but some of them also retained or devel-
oped the habit of bearing handsome flowers — a
habit that would have served small purpose for
the conifers, since insects could not thrive in cold
regions where they remained to battle with the
elements.

Doubtless the most interesting of these trees
that escaped destruction by flight, and the one that
has maintained most fixedly the traditions of the
Mesozoic era is the tulip tree (Liriodendron) .

This beautiful tree, with its unique broad
glossy leaves and handsome flowers is now the
lone representative of its genus. One species alone

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survives as the remnant of a tribe that flourished
abundantly in the Mesozoic age. This species
made its way to what is now the southern part of
the United States, and has kept up its aristocratic
traditions throughout intervening ages of such vast
extent that it staggers the mind to attempt to grasp
their significance.

The thoughtful person cannot well escape a
feeling of awe as he stands in the presence of this
representative of a race that in the main was gath-
ered to its fathers at a time when the ancestors of
man were perhaps still progressing on all fours.

But, traditions aside, the tulip tree of to-day is
a thing of beauty, prized for itself, regardless of
its ancestry. It makes a fine tree for avenue, door-
yard, or park, and it may be grown as far north
as New York and New England.

Being a monotypic tree, one would not expect
it to show very great variation. But no very keen
powers of observation are required to see that the
tulip trees are not identical, and doubtless their
variation is enough to afford opportunities for in-
teresting experiments, though there is nothing on
the earth at the present time with which to com-
bine them.

Exceptional interest should attach to a line of
experiment in which the plant developer is dealing
with racial traditions of such antiquity and such

[296]

An Ornamental from the Tropics

This is one of many unidentified shrubs which have been

received by Mr. Burbank from foreign lands. Unfortunately it

is often impossible for him to obtain the data necessary to identify

plants so received. But all seeds, bulbs or roots sent him

are invariably planted with the hope that

some useful quality may develop.

LUTHER BURBANK

fixity. Meantime, the fact that the tree has a
beautiful flower gives opportunity for a line of
experiment that is usually possible only among
herbs and bushes, inasmuch as most of our trees,
as the reader is well aware, are wind-fertilized,
and hence do not bear conspicuous blossoms.

There are several other trees, however, that
resemble the tulip tree in the matter of blossom
bearing, and that are not altogether unlike it in
general appearance, some of which have corre-
sponding interest, being representatives of ancient
forms, even if not quite rivaling the tulip tree in
the length of their unmodified pedigrees.

The catalpa and the magnolia may be named
as perhaps the chief representatives of these flow-
ering trees. Both of these are represented by
several species, and the representatives of each are
subject to considerable variation.

There are at least two distinct hybrid catalpas,
involving three species, and I have noted great
difference in the rapidity of growth of seedlings;
also variation in color and abundance of flowers,
in length of seed-pods, and in manner of growth
of the trees themselves, some being much more
upright that others.

I have seen magnolia hybrids also, and have
thought it matter for surprise that there are not
more of them, for the trees are readily cross-

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fertilized. Doubtless the fact that different
species bloom at different seasons largely accounts
for the relative infrequency of natural crossing.

There is an opportunity to work with the
catalpa, and I could scarcely mention a plant that
seems to me to give better promise for experiments
in crossing and selection than the great family of
magnolias.

If the seeds are planted while fresh, they germ-
inate readily. The seedlings are easily raised —
almost as easily as apples or pears.

Among the magnolia seedlings now growing on
my grounds, there are some that will grow three
or four feet the first season, while others grow as
many inches. Some have a branching habit, and
others form an upright front. The leaf varies in
breadth and length and in general appearance.
Some are early bloomers and some are late bloom-
ers. There are different shades of flowers. All in
all, there is abundant opportunity for interesting
experiments in selective breeding.

Among other interesting deciduous trees, all of
which afford ready opportunity for experimenta-
tion, are the acacia and its relative the locust (the
seeds of which may best be made ready for germi-
nation by boiling), the alder, which is extremely
variable and with which I have made interesting
experiments; the ash, which affords excellent

[300]

ON ORNAMENTAL TREES

chances for hybridization, and is especially prom-
ising for timber; and the hawthorne, which has
attractive flowers and fruit that are subject to a
wide range of variation, and which has excep-
tional interest because of its not very remote rela-
tionship with the great tribe of trees that furnish
our chief orchard fruits.

The names of the dogwood, the pepper tree, the
tree cranberry and numerous others might be
added, but regarding each of them substantially
the same thing might be said. All offer excellent
opportunities for selective breeding; but few or
none of them have been extensively worked with
hitherto.

The Finest of Ornamental Trees

There is one peerless tree, however, that I must
single out for a few added words of special men-
tion in concluding this brief summary of the more
notable among the ornamental trees.

This is the elm, a tree that occupies a place
apart, having scarcely a rival when we consider
the ensemble of qualities that go to make up an
ideal ornamental and shade tree.

Whoever has visited an old New England
village, and has walked through the corridors of
elms or looked down the vista of streets arched
over by the interlocking branches of the rows of
trees on either side, will not be likely to challenge

[301]

5*

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Mr. Burbank's Hybrid Elm

/r«IA(/ interesting tree was grown from a cutting brought

of ZTuSSSFSFA ^ BY^k' and ^^ on the roots
dinaVg size Th, Sf P^ent tree was a hybrid elm of extraor-
BurbaTk; «niH n h"? thown' which stands bes^e Mr.
wUh »,<? ld homestead" at Santa Rosa, has grown
„%t0msthing raPMitV- Us unique history
gives it altogether exceptional interest.

ON ORNAMENTAL TREES

the preeminence of this tree. Nothing could more
admirably meet the purposes of a shade and
avenue tree.

The English elm, which is a more compact
grower than the American species, has been widely
planted in California. But the American elm
thrives here also, although not native to the coast,
and it is much less subject to insect pests than is
the European species; also the English elm is stiff,
and quite lacking in the graceful lines that the
American elms so naturally assume.

There is a considerable range of variation
among American elms, notably in the size of the
leaves, and the openness or compactness of
growth.

Indeed the variation is so great that it is
never wise to plant a row of seedling elms along a
street or roadside. It is much better in the interest
of uniformity to secure good roots and then graft
them with cions of a single variety.

The slippery elm, which grows in the same
regions with the common American species, is a
tree of more compact growth, but on the whole
not to be compared with the other species. There
are natural hybrids, however, between the Ameri-
can elm and the slippery elm that exceed either
parent in size, and sometimes are of surpassing
beauty.

[303]

LUTHER BURBANK

The largest tree that I have ever seen in New
England was an elm that grew in Lancaster, my
boyhood home, and which I have reason to believe
was a hybrid.

As I was born and brought up under the elm
I have naturally an affection for them greater
perhaps that for any other tree. On a visit to my
old home I secured branches of the gigantic hybrid
and brought them to California, and grafted them
on roots of a seedling of the American elm on my
place at Santa Rosa.

When this grafted tree was only fifteen years
old, it was two and a half feet in diameter. Its
hybrid character was obvious to all botanists who
examined it.

Doubtless this accounts for its extraordinary
rapidity of growth. This was of course a natural
hybrid, but it stands to-day as an object lesson in
the possibility of hybridizing various species of
elms and thus producing a tree of extraordinary
rapid growth.

I have not experimented further with the elm
in this direction; but the hybrid tree that thus
reproduced the personality of a giant elm in the
shadows of which I passed my boyhood — a
souvenir that links the home of my mature years
with the home of my ancestors — is a source of
perpetual pleasure.

_ O^
[End of Volume XI]

♦•°'

***>

A# C. Sto** Colk*

List of

Direct Color Photograph Prints

in Volume XI

Acacia

Page

An Acacia Tree in Bloom 283

Almond

Almond Tree in Blossom 62

Two Almonds — One Showing the Nectarine Color 65

Almonds on the Stem 67

Selected Almonds 70

Another Group of Almond Fruit 73

Some Mammoth Specimens 75

Meats of Selected Almonds 77

Variations in Seedling Almonds 79

The Almond and Its Cousin 81

Seeds of Peach, Nectarines and Almonds 83

Structure of the Almond 85

Leaves of a Peach-Almond Cross 87

A Peach-Almond Hybrid 89

Almonds Grown in Peaches 92

Baler

The Burbank Tree Baler 25

Tree Baler in Operation 28

Ready for Shipment 31

Birch

A Weeping Birch 259

A Branch of the Paper Birch 262

Butternut Tree

A Butternut Tree 139

LIST OF ILLUSTRATIONS (Continued)

Cedar pagc

Cedar of Lebanon 291

Chestnut

A Basket of Chestnuts Frontispiece

A Dwarf Chestnut Tree 6

Six Months Old Chestnut Tree in Bearing 97

Yearling Chestnut Tree in Bearing 99

Branch of a Six Months Old Chestnut 102

A Goodly Crop 105

A "Low Head" Chestnut Hybrid 107

A "High Head" Chestnut 109

Chinquapins and Chestnuts Ill

A Typical Cluster 114

A Well Protected Fruit 116

Chestnuts in the Bur 118

An Impregnable Fortress 121

Exposed Treasures 123

Chestnut Bur of Another Type 125

Bur and Catkin 127

Cypress

Two Cypresses 157

Elder

The Box Elder 287

Elm

Mr. Burbank's Hybrid Elm 302

Evergreen

A Hybrid Evergreen 160

Eucalyptus

A Young Eucalyptus Tree 163

A Row of Eucalyptus Trees 166

Fir Tree

A Fir Tree 241

Balsam Fir Tree 253

Hazelnut

The Hazelnut 145

LIST OF ILLUSTRATIONS (Continued)

Hickory

J Page

A Hickory Tree 130

Hickory Nuts 135

Horse Chestnut

The Buckeye or Horse Chestnut 265

Ivy-Clad Tree

An Ivy-Clad Tree 273

Judas Tree

Judas Tree or Red-Bud 295

Laurel

A Fine Specimen of Laurel 267

Live Oaks

Natural Grafts at the Petrified Forest 190

Live Oak Pasture Near Santa Rosa 299

Magnolia

Japanese Magnolias 281

Maple

A Maple Tree 154

A "Sugar Bush" 256

Nutmeg

The Wild Nutmeg 148

Olive

Olive Trees 247

Ornamental Trees

The Home of a "River Baron" 270

A California Chinquapin as an Ornamental Tree 285

An Ornamental from the Tropics 297

Pecan

A Pecan Tree 142

Pepperwood Tree

A Pepperwood Tree in Bloom 275

LIST OF ILLUSTRATIONS (Continued)

Pine Page

Yellow Pine 171

A Petrified Pine 174

Redwood

A Petrified Redwood 187

Rubber Tree

Tapping the Rubber Tree 238

Sequoia

In Mariposa Grove of Big Trees 169

A Young Giant Sequoia 177

The Largest Tree in the World 180

Another View of the "Grissly Giant" 183

Roots of a "Fallen Monarch" 185

Spruce

A Spruce Tree 244

Sumach

A Selected Sumach Tree in Blossom 293

Tropical Nuts

A Variety of Tropical Nuts 151

Turpentine

Turpentine Trees 250

Walnut

A Walnut Orchard 9

A Franquette Seedling 12

A Heavy Crop 15

Paper Shell Walnuts 18

A Comparison of Leaves 21

The Paper Shell on the Tree 23

Santa Rosa Nut Meats 34

A Foot of Santa Rosa Walnuts 39

Trunk of the Franquette Walnut 42

Trunk of the Black Walnut 45

A Grafted Walnut Tree 48

Parents and Offspring 50

Hybrid Walnuts 53

More Hybrid Walnuts 56

Effects of the Walnut Blight 59

A Row of Paradox Walnuts 197

LIST OF ILLUSTRATIONS (Continued)

Page

A Twelve Year Old Paradox Walnut 201

A Sixteen Year Old Royal Walnut 20G

Nuts of the Royal Walnut 210

Hybrids and Parents 214

A Typical Specimen of the Royal Walnut 219

The Royal Walnut in Winter 224

Another Fine Specimen of the Royal Walnut 229

Foliage and Fruit of the Royal Walnut 232

A Striking Contrast in Seedling 235

Yew Tree

South American Yew Tree 278

Irish Yew 289

f HOPERTY LIBRA*
N. C State Coll