v.3

Clejt Graft

This is one oj several common methods oj grafting.

The engrafted twigs are called cions, the branch on which

they are placed is called the stock. The essential principle is that

the inner bark, called the Cambium layer, oj the cion should be

brought into intimate contact with the corresponding

layer of bark oj the stock. Further details

of grafting are shown in other

pictures in this volume.

LUTHER BURBANK

HIS METHODS AND DISCOVERIES AND
THEIR PRACTICAL APPLICATION

PREPARED FROM

HIS 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 III

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

MCMXIV

Copyright, 1914, by

The Luther Burbank Society

Entered at Stationers' Hall, London
All rights reserved

• -: ; :
- •* •/ j •'

Volume III — By Chapters

Foreword ............................. Pae 3

I Planning a New Plant

The First Step
Practical Work

—The First Step in «

i

II Plant Affinities

— Choosing the Lines of
Least Resistance

III Practical Pollenation

-A Survey of
Working Method .

IV Quantity Production

-On Seedlin
Their Care

— A^ Survey of r/y

— On Seedlings and (\Q

V Grafting and Budding

— Short-cuts to
Quick Tests

VI Letting the Bees Do Their Work

—Nature Will Help Us

All She Can

VII Fixing Good Traits

— How to Hold a Result

Once Achieved

VIII Recording the Experiments

—Easy Wayi
Keep Trai

IX Final Selection

— The Most
Work of A

List of Direct Color Photograph Prints 305

— Easy Ways to

Keep Track of Progress . .

— The Most Important
Work of All ....

340358

FOREWORD TO VOLUME III

With many examples of the actual work before
us, Mr. Burbank now takes us into the interesting
detail of method itself, treating the subjects of
pollenation, grafting, plant affinities, fixing traits,
selection, and spreading before us all of the
processes which he has employed in his more than
100,000 separate experiments.

The purpose has been to lead the reader, by
easy and interesting stages, up to a point where
a delineation of the actual processes may be most
readily grasped. This, the third book, completes
the consideration of general method, and with the
two preceding volumes gives us an intelligent
survey of Mr. Burbank's work.

THE EDITORS.

A Burbank Strawberry

This picture represents a Jruit that was developed

in accordance with Mr. Burbank's preconception as to what

a perfect strawberry would be like. It is remarkably symmetrical in

shape, of just the right size, and its qualities oj Jirmness oj

texture and of flavor are ideal. It is the product of a

long series of experiments in selective Breeding.

John Burroughs pronounced it the best

strawberry he had ever eaten.

PLANNING A NEW PLANT

THE FIRST STEPS IN PRACTICAL WORK

SOMEONE has said that a painter is a man
who can see the picture in the landscape.
In similar fashion it may be said that a
successful plant experimenter is one who can see
new varieties of future plants when he looks at
old existing varieties.

But of course the painter, whatever his con-
structive imagination, does not always see at first
glance every detail of form and color that will
ultimately appeal to him. Nor can the plant
experimenter claim, by any manner of means, to
know always from the outset just what his new
plant creations will be like. There are numberless
instances, indeed, in which a plant experimenter
who operates on a large scale may make hybrid-
izing experiments, merely to test the possibilities
of crossing certain species, without having any
precise and definite goal in view.

[VOLUME III— CHAPTER I]

LUTHER BURBANK

But, on the other hand, it is necessary in the
pursuit of practical plant developments to have
a tolerably precise idea in mind as to the
particular direction in which progress is desirable.

Lacking such an ideal, the breeder of plants
would be about as likely to produce new creations
of value as an architect would be likely to
construct a fine building by putting materials
together at random without a carefully precon-
ceived plan.

"In what percentage of cases have you achieved
the ideal at which you aimed in the production
of new varieties of flowers or fruits?" a visitor
asked me.

The question is almost impossible of definite
answer. When I first commenced, doubtless a
very small proportion of my experiments came
out as I expected. But now, with years of experi-
ence to guide me, I may say that I practically
always get something not far different from what
I desire. In many cases, the result comes just
about as I expected. But this is because I am
working with plants that I have previously tested.

With a new plant I am still sometimes in
doubt. But if it is a case of poppies or walnuts
or any one of a score or so of other plants that
I have fully tested, I know just about what to
expect.

[8]

PLANNING A NEW PLANT

At best, however, I am very often reminded
that each species has its own individuality and
that even the most familiar plant may hold
surprises in store for us.

THE ROUGH SKETCH

"But just how do you start out when you are
seeking to create a new form of plant life?" I am
constantly asked.

And here again the answer is difficult. Every-
thing depends upon the ultimate object. If I am
seeking merely to test the possibilities of making
certain crosses, or as it were feeling my way
along new channels, I am more or less like a
person groping in the dark.

This form of vague experimentation is often
full of interest. I have already given some
instances of what may come to pass when we
hybridize plants of widely separated species or
of different genera. The reader will recall the
case of the petunia with the tobacco habit and
of the dewberry crossed with such remote cousins
as apple and pear and mountain-ash. These
experiments were made without a clearly defined
object — except to ascertain whether it was possible
to hybridize plants of such diverse character.

And the results of the experiment, while of
very great scientific interest, were not practically
successful in a commercial sense.

19]

LUTHER BURBANK

I recall reading an address by the late
Professor Newton, a distinguished American
astronomer, on the subject of "dead work," in
which he emphasized the fact that the main bulk
of the experiments which any scientific worker
must make will lead to no definite goal. A large
part of the time of every experimenter must be
given up to following trails that lead nowhere in
particular or that end in blind cul de sacs.

The work of the plant experimenter is no
exception, but there is always an incentive to
further effort in the knowledge that a path that
seems to lead only into impenetrable mazes may
presently bring one out into the light. To make
the application to one illustrative case among
many, I recall that for twenty-four successive
seasons I attempted to hybridize certain species
of Solanum before I finally succeeded in effecting
a cross that gave me a single seed from which
sprang the new race of Sunberries.

But it must not be understood that the main
bulk of my experiments are made in any hap-
hazard manner.

On the contrary my most important results
have been attained by continuing the experimen-
tation along rigidly predetermined lines and by
methods of hybridizing and selection that my
earlier work had fully established. Having served

[10]

Strawberries Showing Variation

This picture illustrates the variation that may be

shown by fruit growing on vines from the same lot of seed.

By selection, each type of berry here shown might have its peculiarities

accentuated, and as many new varieties developed. Mr.

Burbank is always on the lookout Jor variation among

his plants, and such variation Jorms the basis

of his experiments in selective breeding.

LUTHER BURBANK

a long apprenticeship and tested the usual limits
of making new plant combinations, I was presently
able, like any other trained technician, to apply
the knowledge thus acquired toward far more
definite results than were at first possible.

In the case of the Shasta daisy, the plans were
all laid out beforehand as to just what type of
flower I wished to produce.

The ideal of a white blackberry was also, of
course, a perfectly precise and definite one.

Obviously the scented calla, the stoneless plum,
the early bearing cherry, the sugar prune, and the
spineless cactus are other instances in which the
ideal pursued was as clearly conceived and as
definitely outlined in advance of my earliest
experiments as a cathedral is outlined in the
mind of the architect before he commences his
preliminary drawings.

In one case as in the other the details may
be modified as the work progresses, but the
general idea of the structure aimed at — be it new
fruit or new building — must be conceived with a
good deal of definiteness from the outset. My
original conception of a new plant creation, in
the cases outlined and in a large number of others,
certainly bore as close a resemblance to the final
product achieved as the first rough drawing of the
architect bears to his finished plans.

[12]

PLANNING A NEW PLANT

"But how do you begin? What is the very first
thing?" a visitor insists.

The "very first thing" I have already described
— it is the conception of an ideal, a mental picture
of the new plant form desired.

CLUES TO BE FOLLOWED

It has occurred to me, for instance, that the
cherry crop is not what it might be. I have
learned that there is a steady market for early
cherries and that a difference of a few days in
the time of marketing may make a difference of
more than one hundred per cent, in the price.

And so I ask myself, why not create a new
cherry that shall be ready for shipping at least
two or three weeks earlier than any cherry now
in the market?

Of course, I reflect that my early cherry must
have a number of other desirable qualities — large
size, rich color, lusciousness of flavor. I know at
the outset, or I presently learn, that it is desirable
also, from the standpoint of the shipper, that my
cherries shall grow on short stems. I know that
the tree producing them must be hardy, capable
of withstanding both cold winters and dry sum-
mers, and that it must have an inherent vitality
that will make it resistant to the attacks of insects
and fungoid pests.

Next I ask myself what warrant there is for

[13]

LUTHER BURBANK

supposing that I can build such a fruit-structure
as I have conceived.

And here the answer is supplied solely by
the use of imagination in connection with the
inspection of existing races of cherries. I examine
the best fruits already in the orchard and find
that there is a large measure of variation between
the cherries grown on different trees, as well as
between the individual specimens on the same
tree.

In imagination I look back far into the past
and inquire as to the racial history of this fruit.

I am led to believe that certain among the
ancestors of the cherry have grown in semi-
tropical climates, and I know that even in the
present day there are species, doubtless sprung
from the same original stock, that grow far up
into Canada.

I ask myself why it is that the cherry shows
such a propensity to vary, and I find an answer
in the assumption that the existing cultivated races
carry in their veins, so to speak — that is to say in
their germ plasm — hereditary tendencies drawn
from varied strains of a mixed ancestry.

And I feel well assured that it should be
possible, by accentuating the tendency to varia-
tion through further hybridizing, and by careful
selection, to combine and bring out in a more or

[14]

LUTHER BURBANK

less remote generation of progeny of the existing
cherries, a race that will furnish extreme
examples, through reversion, of the limits of
variation in each direction — and as regards each
particular quality of fruit — that any ancestor
reached.

It will be obvious, then, that I am not preparing
to make bricks without straw.

I am counting well the materials with which
I must work, just as the architect from the first
stroke of his pencil bears in mind the materials
of the future cathedral.

I do not imagine that I can produce an apple
from my cherry stalks, any more than the architect
assumes that he can build a marble cathedral out
of bricks. I know that there are sharply defined
hereditary limitations beyond which the cherry
cannot be made to go within any such period of
time as that limiting my experiment.

In other words, I do not ask the impossible,
although it has often seemed to my critics that
I have asked the highly improbable.

But the results I have attained are in them-
selves sufficient answer to the critic. If my vision
has in some cases been the clearer, it is merely
that my knowledge of plant life, drawn from the
school of experience, has been wider.

To the uninitiated observer it may have seemed

[16]

PLANNING A NEW PLANT

that I set no limits to the transformations I
attempted. In reality, my plan has always from
the outset recognized most definite limits—
although often enough the limits as I conceived
them were quite different from those that had
been set by theoretical botanists.

AID FROM GALTON'S LAW

In attempting to estimate the possibility of
improvement in a given form of plant life, it is
of value to recall the formula put forward by the
late Sir Francis Gal ton; a formula often spoken
of as Gallon's law.

According to this estimate, the hereditary traits
of any given organism are so intermingled that
we may assume as a general rule that offspring
of a given generation will inherit about half their
tangible traits from their parents, one-quarter
from their grandparents, one-eighth from their
greatgrandparents, and so on in decreasing scale
from each earlier generation.

Stated otherwise, according to this rule, we
should be able by observation of the parents of
any given organism, to see presented half of the
traits of the offspring; but we may expect that
the offspring will manifest, as the other half of
their inheritance, traits that have come to them,
through the process of reversion or atavism, from
remoter generations of the ancestral strain.

[17]

LUTHER BURBANK

And this obviously gives opportunity for the
appearance of an enormous variety of traits in
any given generation that were not manifested in
the preceding generation.

Thus any given individual has normally, as
a moment's reflection will show, four grand-
parents, eight greatgrandparents, sixteen ancestors
in the generation before that, then thirty-two,
sixty-four, one hundred and twenty-eight, and
so on in a geometrical ratio with each remoter
generation. So the normal ancestral clan of any
one of us numbers more than a thousand different
individuals within the relatively limited period of
time compassed by ten generations.

And, according to the estimate of Galton, to
which numberless cases of atavism give force,
certain traits and tendencies of each and every one
of these ancestors may make themselves manifest
in the personality of any given descendant.

Galton's studies, upon which his formula was
based, were chiefly made with reference to human
beings, but we now know that the laws of heredity
apply with equal force to all kinds of living
organisms, including plants; and whatever the
limitations of Galton's law as a precise formula,
there can be little question as to the general truth
of the principle that he invoked.

Hence the value of that search in imagination

[18]

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LUTHER BURBANK

for the ancestors of our cherry in their widely
separated habitats and with their widely diversi-
fied traits and habits.

But of course in making practical studies for
the development of the mental blue print with
its forecast of qualities of our new cherry, we
must perforce be guided largely by the observed
qualities of the parent stock with which we deal.
Precisely what were the qualities of the remote
ancestors, we can only infer. But we can see
for ourselves what are the qualities of the fruit
before us.

We know, then, pretty definitely what we may
expect as to one-half the traits of a hybrid that
will result when we cross two varieties of cherries
in our orchard. The other half must be somewhat
matter of conjecture, to be revealed by the
actual product or, as is practically the case, by
succeeding generations.

What we actually do, then, in practice, is to
take flowers from a cherry tree that has been
observed to bear fruit somewhat earlier than
neighboring trees, and with this pollenize flowers
of another tree that has been observed to produce
fruit of exceptionally good quality. Pollenation
accomplished, by the method elsewhere described,
we can only mark the branch for future identifi-
cation, and await results.

[20]

PLANNING A NEW PLANT

The seed thus secured will be planted next
season, and in due course we shall have a seedling
which, when grafted on another tree to speed its
maturing, will come to blossoming time — after
another period of waiting — and finally show us
the first fruits of our experiment.

From this fruit we shall raise a new generation
of seedlings which will reveal to us beyond
peradventure a varied assortment of ancestral
traits that the parental forms of our first hybridi-
zation did not show. And from among these
diversified forms, we shall be able, by a long series
of selections and new hybridizations, to make our
way toward the attainment of our original idea.

The precise steps and the varying details
through which this may be attained, will be dis-
cussed in other chapters. Here we are concerned
only with the general outline, and, this having
been presented, we may leave our cherry in this
interesting stage of partial construction.

To be sure we have not seemingly advanced
very far toward our ideal in these two generations;
but in this our case is only comparable, after all,
to that of the architect, who, when he has planned
a building that shall ultimately tower toward the
skies, must be content to see the workmen first
begin digging in the opposite direction, to lay
foundations far beneath the earth's surface.

[21]

LUTHER BURBANK

This matter of the very doubtful result of the
first stages of a hybridizing experiment should
be emphasized, because otherwise the amateur is
pretty sure to become discouraged at the outset
and to proceed no farther.

Many an experimenter has given up a quest
because when the two varieties of plant were
crossed the offspring seemed inferior as to the
desired quality to either of the parents. But the
experienced plant breeder knows that this is very
often to be expected and that he should not be in
the least discouraged by this result. It is necessary
to go on to the next generation before we can
hope to discover the real possibilities of the
experiment.

The simple fact is that, where varieties or
species of plants that differ markedly as to certain
qualities are hybridized, the offspring very fre-
quently seems to present what has been spoken of
as a mosaic of characters rather than a blending.
It may and very commonly does manifest, as
regards any given quality, the influence of one
parent seemingly to the exclusion of the other.

A familiar illustration of the same rule may
be observed when a person having black eyes
marries one having blue eyes. It is obvious that
no individual child of this union can have both
black eyes and blue eyes. In point of fact, it is a

[22]

The Chinese Pear

The Oriental pears have not the characteristic shape
oj the European pear. The latter was presumably modified
in shape through selection at a comparatively recent period. It is
supposed that the original home of the pear was Central Asia,
and that the fruit was carried into Europe in prehistoric
times. The pear is characterized by having a
fibrous or woody deposit in the skin, indi-
cated by the dotted appearance oj
this Oriental specimen.

LUTHER BURBANK

matter of common observation that the offspring
in such a case will have dark eyes.

But it has also been observed that the blue
eyes of one of the parents may reappear in the
second generation.

The tendency to blue eyes was entirely subordi-
nated or submerged in one generation, yet it was
by no means eliminated, as its reappearance in the
next generation clearly proves.

Similar instances without number may be
studied from our plant experiments; for example,
the case of the white blackberry. If flowers of
this kind are fructified with pollen from flowers
of a blackberry of the usual color, the hybrid
progeny of the first generation will all bear black
fruit.

The quality of blackness has proved prepotent
or dominant, and the opposed quality of whiteness
has been totally subordinated so far as this
generation is concerned.

But if these black hybrid blackberries are
cross-fertilized, from the seed thus produced there
will spring a generation of brambles, some mem-
bers of which will in due season produce white
fruit precisely like that of the maternal ancestor.

Such, it will be recalled, was indeed the
experience in the development of my new race
of white blackberries.

[24]

PLANNING A NEW PLANT

To instill good qualities of fruit into the
inferior original berry, it was necessary to cross
with the large and well flavored Lawton black-
berry.

The immediate result was seemingly to oblit-
erate the white-fruiting tendency altogether.

But a wide experience of similar instances led
me to continue the experiment, which for the
moment seemed to be carrying me away from my
ideal of a white blackberry; and the principle of
reversion came to my aid in the next generation
and gave me, as will be recalled, a berry that
combined the light color of one of its grand-
parents with the size and flavor of the other.

I have already suggested that it aids the
memory, and helps to give tangibility to the facts,
to recall the Mendelian phrase which speaks of
blackness versus whiteness in such a case as
constituting a pair of unit characters; naming
blackness as the dominant and whiteness as the
recessive feature; and which gives us assurance
that a fruit which shows the recessive character
of whiteness in the second generation will there-
after breed true, thus affording us evidence of
definite progress toward the ideal of our experi-
ment.

AID FROM UNIT CHARACTERS

As the principles that govern these cases are

[25]

LUTHER BURBANK

of very wide application, it follows that there is
very great advantage from the standpoint of the
plant developer, in the discovery of pairs of unit
characters and the demonstration of their relation
toward each other as regards dominance and
recessiveness.

An interesting illustration of this is afforded
by the experiments made by Professor R. F. Biffin,
of Cambridge University, in the successful attempt
to develop a new race of wheat.

Professor Biffin through a series of experi-
ments showed that when beardless ears of wheat
are crossed with bearded ones, the beardless
condition proves dominant, so that all the off-
spring are smooth-eared; but that the recessive
quality of bearded grain reappears in the second
generation.

The same thing held true for various other
pairs of unit characters, such as red chaff versus
white chaff, red grain versus white grain, hollow
stem versus solid stem, and the like.

Professor Biffin was able to make an imme-
diate practical application of his experiments
through which he developed a new race of wheat
that is proving of great economic importance. It
appears that the best races of British wheat have
been peculiarly susceptible to the fungous pest
known as rust. There are, somehow, certain races

[26]

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of wheat that are immune to the pest; but unfor-
tunately these produce a very poor quality of
grain.

Professor Biffin found that susceptibility and
immunity to rust constitute a pair of unit char-
acters, in which susceptibility is prepotent or
dominant.

When he crossed the susceptible grain with
the immune one, he therefore produced an entire
generation of susceptible grain.

His experiment had seemingly gone backward,
quite as in the case of my first generation of white
blackberries.

But in the ensuing generation the recessive
character of immunity reasserted itself; and,
combined with this desired character, in a certain
proportion of the progeny, there appeared the
other desired quality of a good head of grain of
fine quality.

So by the application of this principle of the
segregation and recombination of unit characters
Professor Biffin produced a new race of wheat
in two or three generations, and this new race
of wheat breeds true.

We shall see this principle illustrated over
and over in connection with the long series of
my plant experiments.

In case of the wheat, as in that of my white

[28]

PLANNING A NEW PLANT

blackberry, the process was relatively simple
because we were dealing only with two pairs of
unit characters. Moreover, the case of wheat is
further simplified by the fact that this plant is
self-fertilized and under conditions of cultivation
has become a very fixed race, little subject to
variation.

When we deal with races of fruits that tend
to vary almost indefinitely, and when further we
are concerned with ten or a dozen unit characters,
the matter becomes vastly more involved, as we
have previously seen illustrated.

But the amateur will do well to begin his
experiments with simple cases, dealing with only
a single quality, say a particular color of flower,
that he may thus learn to distinguish the prin-
ciples here enunciated. In due course he may go
on to apply these principles to more complicated
experiments in plant hybridization. But unless
he learns at the outset that certain characters
that are submerged in the first hybrid generation
will inevitably reappear in the second, he will
constantly blunder in his interpretation of tenta-
tive results.

On the other hand, when he has learned to
gauge his second-generation hybrids correctly,
he is on the highway to success as a plant experi-
menter.

[29]

Common, French, and Burbank Mangolds

The large double Burbank marigolds have been developed from
the small single flowers through selective breeding. By cross-fer-
tilizing different varieties, a tendency to variation is induced, and by
preserving /or seed purposes only those flowers which vary in
the desired direction, any given quality is accentuated, until
finally such a metamorphosis as this is brought about.
The rapidity of development varies with different
plants, but many generations are required
to produce such a transformation
as that shown in this picture.

PLANT AFFINITIES

CHOOSING THE LINES OF
LEAST RESISTANCE

WHY do not plants hybridize in a state
of nature?" a visitor asked me. "You
seem to get most of your new varieties
by hybridizing old ones. Why does not Nature
take a leaf from your note-book and produce new
species in the same way?"

And I was able to inform my facetious ques-
tioner, much to his surprise, that the method he
suggested was one that Nature had practiced from
the beginning, and is constantly practicing all
about us.

We were standing near the gateway of my
Sebastopol place. I pointed out across the road.

"Why, just over by the roadside," I said, "you
may see for yourself precisely such an experiment
in hybridizing as I have made in the case of
thousands of plants. Do you see those tarweeds
there? Doubtless you are familiar with them.

[VOLUME III — CHAPTER II]

LUTHER BURBANK

"There are two common species growing there
together. One of them has large showy flowers,
the other small and inconspicuous ones. The
botanist calls the large flowered species Madia
elegans, and the other M. saliva. The two species
do not look much alike, and some botanists even
classify them in different genera.

"If you look at all closely you will see that
there is a third form of plant, bearing some
resemblance to each of them, growing among the
others, and I can assure you that this is a natural
hybrid between the two.

"If you examine this hybrid, you will find that
its branches are less spreading than those of its
large-flowered parent, although not upright like
those of the other parent; and that the stem is
stouter than that of either parent. As to foliage,
the hybrid plants have larger and thicker leaves
than those of the large flowered tarweed, more
closely resembling the other species in this
respect, but the ray-flowers are intermediate in
size and shape as well as color, the reddish-
brown that characterizes the flower of the more
conspicuous parent being reduced in the hybrid
to a spot just in the top of the tube.

"So here you are probably witnessing the
creation of a new species in nature. You, of
course, are an evolutionist and therefore are

[32]

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aware that all species of plants as well as animals
have been evolved in past ages by a development
from earlier forms, but you very probably sup-
posed that this creative process has now come
to a standstill. Let me assure you, then, that this
process is going on to-day very actively, in all
probability quite as actively as at any time in
the past.

"Species of plants in a state of nature are
constantly hybridizing, and new species are
being developed under our eyes.

"There is nothing anomalous about the case
of the tarweeds, although they afford a very
interesting illustration of the development of
which I speak. The same thing may be observed
in the case of certain genera of the mint family.
Here in some cases the hybrids thrive almost to
the entire exclusion of the parent species. In
other cases they gradually disappear, being too
unstaple to establish themselves by seed.

"Everything, of course, depends upon the
qualities of the hybrid. If it is well adapted to
the environment it survives. If better adapted
than its parents, it probably runs them out alto-
gether. But, on the other hand, if the hybrid
is less well adapted than the parent forms to
make its way in the world, it is of course weeded
out by natural selection."

[34]

PLANT AFFINITIES

In response to a further query, I named for
my visitor, among plants that often hybridize in
a state of nature, the various species of the genus
Rubus, including the blackberry, raspberry, the
tribe of wild roses and crabapples; the California
lilac, the various members of the oak tribe, the
willow, the strawberry and the huckleberry; nor
are these all — the list might be almost indefinitely
extended.

Indeed, it is my firm conviction that hybrid-
izing between natural species is a phenomenon of
almost universal occurrence.

I believe that no other equally plausible
explanation has been given of the appearance
of seeming spontaneous varieties or mutations
that furnish the material for the operation of
natural selection, and are thus the basis of
organic evolution.

It is true that such a suggestion as this
would have seemed heretical not very long ago;
but vast numbers of experiments in hybridizing
different species, and even representatives of
different genera, in my orchards and gardens
have afforded a mass of evidence that no one
can ignore. So to-day it is coming to be recognized
more and more generally that the hybridizing of
wild species is Nature's conventional method of
producing variability, and, as it were, testing out

[35]

LUTHER BURBANK

the environment by supplying new forms that
come in competition with the ones already
developed.

LIMITS OF HYBRIDIZING

But why then, you will perhaps ask, does not
the production of new forms between natural
species take place so universally as to disturb the
entire scheme of organic nature. In point of fact,
the zoologist and the botanist are able to describe
vast numbers of species, each of which has certain
fairly well-defined characteristics and differs in
certain definite regards from other forms.

It is true that the more closely the matter is
studied the more commonly varieties are found
that manifest characteristics intermediate between
those of the supposedly fixed species. But even
when these are taken into consideration, it still
remains true that the word "species" as applied
to a vast number of familiar forms of vegetable
and animal life, has a pretty definite and tangible
meaning.

How is this possible, if the interbreeding of
species is a universal phenomenon?

The answer is found in the facts (1) that the
hybrid forms produced when species in nature
are crossed, for the most part quickly disappear
because they are not an improvement, from the
standpoint of adaptation to their environment,

[36]

= S c

*e - i Fe s-1 1 «-Il?

§ S

LUTHER BURBANK

on the parent forms; and (2) that limits are
imposed by the relative lack of affinity of one
species for another.

As to the first point, it must be recalled that
each existing species has been produced only after
long generations of struggling against adverse
conditions. Constantly there is a tendency to
variation within certain limits even in the case
of the most fixed species. Such variations con-
stitute tests of the fitness of the species to live
in the environment in which it finds itself. Favor-
able variations are preserved by natural selection,
simply because they have the capacity to outgrow
the original form, or outlast it in times of drought
or other hardship.

And so every existing wild species proves by
the very fact of its existence that it has a large
measure of adaptability to the existing envir-
onment.

It is always improbable, then, in the nature
of the case, that any new intermediate form such
as would arise from hybridizing two allied species,
will be better adapted to survive than the parent
form. Such cases do arise, else we should have
no new species, but in general the rule holds. So
we may fairly count it exceptional if a hybrid
between natural species survives beyond the first
or second generation.

[38]

PLANT AFFINITIES

The struggle for existence is always keen, and
the individual organism that lacks ever so little
of equaling its fellows in vitality and responsive-
ness to its environment must inevitably perish.

Nevertheless, the experiment of producing
new forms through the hybridizing of old ones
is perpetually being made, and must continue to
be made, if existing forms are to remain plastic,
ready to take advantage of the changed conditions
of environment; ready, that is to say, to evolve
in future as they have evolved in the past.

But there are limits beyond which this per-
petual experimentation with new nascent species
could not advantageously be carried, and so
nature puts a sharp limitation upon the extent to
which the experiment may be undertaken.
AFFINITY FOUNDED ON COUSINSHIP

And this is done by the simple procedure of
making it increasingly difficult for species to
interbreed in proportion as the species become
divergent in character.

Tarweeds, for example, may interbreed among
themselves, and various species of mint may
similarly interbreed, but no species of tarweed
could hybridize with a species of mint. One
member of the rose family may hybridize with
another — blackberry with raspberry, let us say,
or quince with apple; and in the same way dif-

[39]

LUTHER BURBANK

ferent species of oak may interbreed; but the
hybridizing of apple or blackberry with any
species of oak is almost unthinkable.

Similarly, in my experiments I have been able
to hybridize peach with almond, and almond with
plum, and plum with apricot; also apple with
quince, and quince with pear. Stone fruit with
stone fruit, that is to say, and seed fruit with seed
fruit— but never stone fruit with seed fruit.

In a word, the possibility of cross-fertilization
between species is conditioned on a certain close-
ness of relationship, which we speak of as affinity.

This, as the evolutionist teaches us, is a matter
of actual genetic relationship. All members of
the rose family, for example, have branched from
the primal ancestral stem at a period much more
recent than that at which the common ancestor
of the present-day apple and rose and blackberry
branched from the primal stock of, let us say,
the oaks.

In the broadest view, there is a cousinship
between all species of plants; just as there is
relationship between all the twigs of an actual
tree. But the species of an existing genus may
be likened to twigs on a single branch; other
genera representing different branches which
may diverge in opposite directions, and only come
together at the trunk.

[40]

Corn Tassels Bearing Kernels

Among the most interesting of Mr. Burbank's

experiments with corn are those in which the tassel of the

corn, which in the cultivated plant bears pollen only , has been induced

to develop pistillate flowers and seeds. This is a reversion to

the ancestral form in which the seeds were borne

at the tip of the stalk, as is still the

case with most other grasses.

LUTHER BURBANK

Then, too, there is a time element involved.

Species that are closely similar in appearance
are those that have branched from the ancestral
stem in relatively recent epochs; species more
distinct trace their cousinship through remoter
lines; and forms so widely diverse as to be placed
in different orders have been separated for still
longer periods. And we must suppose that in
each generation the new forms have taken on a
modicum of new traits, and have tended to fix
the divergence of earlier traits through which they
attained specific difference.

In due course, then, it comes to pass, that a
given form has branched so widely from its
cousins that the harmony of purpose, so to speak,
that once obtained between them no longer
obtains.

The racial memory as to ^ their common
ancestry has become blurred, if the phrase be
permitted, and each species has become so fixed
in its own manner of life that no compromise
between them would be possible.

And so we find, in point of fact, that it becomes
increasingly difficult to hybridize species that are
obviously widely divergent in form of stem and
foliage and flower, and that in a vast number of
instances any attempt to hybridize these forms is
altogether futile.

[42]

PLANT AFFINITIES

It must be understood, however, that it is by
no means always possible to predicate, from
observation of a given pair of more or less
distantly related species, whether or not the two
would be mutually sterile. Sometimes the experi-
ment results in a surprise, and we are able to
produce offspring when the cross seemed alto-
gether improbable.

Such was the case, it will be recalled, with
my experiments in hybridizing the dewberry with
the pollen of the apple and pear and rose and
mountain-ash. Such was the case also with the
cross which resulted in producing the sunberry,
and with that which developed the plumcot.

In "each of these cases, to be sure, the pistil of
one plant accepted the pollen of the other, as it
were, unwillingly. But persistent effort effected
the desired resfult, and in the three instances
last mentioned fertile offspring were produced.
Possibly these might not have survived in the
state of nature, but under the conditions of
artificial selection they provided the foundation
for the development of what may fairly be con-
sidered new species.

PLANT ANTAGONISMS

The characteristics that make it impossible to
hybridize two species that have varied beyond
certain limits are sometimes physical.

[43]

LUTHER BURBANK

Thus it may chance that the two species have
developed the habit of blooming at different
times. If the flowers of a given species are alto-
gether out of bloom before the flowers of another
species open, it is obvious that, in a state of
nature, hybridizing between these species will
never occur, however close their affinity. Simi-
larly there are two closely related species of
evening primrose that are not hybridized under
natural conditions because the flower of one
opens only for a brief period at midday and that
of the other only during the night.

Again it occasionally happens that the physical
structure of the style which carries the pollen
tube to the ovules is such as to prevent the
carrying out of this essential process. In the case
of a large pollen grain and an exceptionally
slender style, it is probable that the fructifying
substance of the pollen is debarred from finding
its way to the ovule.

Such cases are probably exceptional, however,
and the usual barrier erected by Nature between
species is not so much physical as chemical. That
is to say, the antagonism is inherent in the plants
themselves.

Allied species are of such chemical constitu-
tion that the protoplasm from one mingles readily
with protoplasm from the other.

[44]

Corn Tassel Growing From the Ear

This reverses the condition shown on page 41.

Here also the pollen-bearing tassel and the grain-forming

ovules are together^ but they are located in the axils of the leaves instead

oj at the tip of the stalk. This anomaly illustrates the mixing

up of hereditary pendencies that may take place when

different species are hybridized. The mingling

of the strains of the primitive Teosinte

and the cultivated corn brings out

latent hereditary tendencies.

LUTHER BURBANK

In the case of more widely divergent species, it
may come to pass that the juices of one plant are
actually poisonous to another. In such a case it
is futile for the pollen grain and pistil to meet,
because no fertilizing influence will be trans-
mitted.

Even if the degree of chemical antagonism
developed has not reached a stage that makes
fertilization wholly impossible, it may be suffi-
cient to prevent the development of a thrifty
offspring.

Or, as is quite usual, it may result in the
sterility of the hybrid progeny, and thus put a
barrier upon farther advance along that line.

If proof were needed that such a chemical
antagonism prevents the cross-fertilization of
species separated too widely, further evidence
may be found in the negative results that attend
the attempt to graft a branch of one of these
species upon the stock of the other.

Generally speaking, it will be found that
species that cannot be cross-fertilized, also cannot
be cross-grafted.

In exceptional cases, it is possible to effect the
graft where efforts at hybridization have proved
futile. Such was the case, for example, with my
grafted tomato and potato vine. But in general,
the plant that refuses to mate with another plant

[46]

PLANT AFFINITIES

refuses also to accept its stem as a companion
organism when grafted or budded.

However carefully the grafting experiment
may be performed in such a case, the uncon-
geniality between stock and cion is soon made
manifest. The surfaces do not unite; or if union
takes place there is but slight tendency to grow;
or the cion does not thrive, and is presently
blighted.

There are all gradations — from actual poison-
ing in which there is no tendency whatever to
unite, to a partial or even temporarily complete
union, followed by separation even after years of
growth — according to the degree of antagonism.

This chemical antagonism between the tissues
of the plants themselves affords the surest evi-
dence of the long periods of time during which
the two species have lived under more or less
divergent conditions, and have been occupied,
each in its own way, in the development of new
characteristics. Yet that such intimate differences
of constitution should obtain between species that
show many outward points of resemblance must
always be matter for surprise to the plant lover
whose attention is called to it for the first time.

That this intimate record of grades of
cousinship should be permanently graven in the
protoplasm of the plant itself is one of the most

[47]

LUTHER BURBANK

mystifying and thought-compelling of biological
revelations.

If any one were to doubt that the intimate
chemical structure of plant protoplasm and plant
juices may thus be depended on to reveal genetic
relationships, and to mark nice shades of distinc-
tion between allied forms, evidence from a quite
alien field might be cited that would set the matter
at rest.

EVIDENCE FROM THE ANIMAL WORLD

The evidence in question is furnished by an
extraordinary series of blood tests through which
Dr. G. H. F. Nuttall, the American Professor of
Biology at Cambridge University, has traced the
intimate relationship of large numbers of animals
of different orders.

By inoculating rabbits with the blood of dif-
ferent species of birds, reptiles, and mammals,
Dr. Nuttall was able to develop an extraordinary
serum with which the intimate constitution of the
blood of other species of animals could be tested.
He thus demonstrated, for example, that lizards
and serpents are more closely related than turtles
and crocodiles, but that all these reptiles are
nearer to one another than they are to birds, and
nearer to birds than to mammals.

He showed that the dog carries in every drop
of its blood chemical proof of closer relationship

[48]

ll|tr|?'!.9^il

-a1-S*3*8'8

S>

LUTHER BURBANK

with wolves, and foxes, and jackals of every
species than with any member whatever of the
cat family. Similarly, all cats — tigers, lions,
leopards, along with the domestic tabby — give
proof, in the chemical constitution of their blood,
of a common origin. And, bringing the com-
parison still nearer home, the blood of man is
more like that of the chimpanzee, the gorilla, and
the orang, than it is like that of any other
creatures; and the monkey tribes of the Old
World are more manlike in the constitution of
their blood than are the monkeys of the New
World.

Dr. Nuttall's experiments comprised sixteen
thousand individual tests, with a total of at
least 586 species of mammals, birds, reptiles,
batrachians, fishes, and crustaceans, coming from
all parts of the globe. The biological implications
of his experiments have been commented upon
as follows:

"Doubtless some hundreds of thousands of
years have elapsed since the direct ancestors of
men branched from a common stem with the
direct ancestors of the gorilla. There has been
no blending of blood in the intervening centuries.
Cats have been cats and dogs dogs from geological
epochs so remote that we hesitate to guess their
span in terms of years. So the intimate chemical

[50]

PLANT AFFINITIES

qualities that denote man or ape or cat or dog,
each in contradistinction to all the others, must
have been transmitted unmodified through count-
less thousands of generations.

"It taxes credulity to believe that such intan-
gible properties could be transmitted unmodified
through the blood streams of such myriads of
individuals; but the evidence of the test-tubes
proves that this has been done.

"What makes the marvel greater is the fact
that the bodies of the animals have meantime
been so modified as to develop utterly divergent
species — for example, the lion, the tiger, the
puma, the leopard, and the house cat; different
types of dogs, wolves, foxes and their allies. But
in each case some intangible quality of the blood
remains unchanged to prove the common origin.
Blood is indeed thicker than water."

The bearing of these extraordinary experi-
ments upon the case in hand will be obvious.

If animals carry in their veins generation after
generation, through untold thousands of years,
these intimate chemical conditions, then the same
thing may well be supposed to be true of plants.
And so the affinity shown between species that
can be hybridized, and the antagonism between
species that refuse to hybridize, can be explained
on the basis of a fundamental intrinsic quality of

[51]

LUTHER BURBANK

the protoplasm that is the foundation substance
of life.

This gives us a more profound and compre-
hensive appreciation of the word "affinity" as
applied to various species of plants than we could
otherwise have.

It also makes it in a measure comprehensible
that the traits of remote ancestors should be
carried latent in the tissues of the germ-plasm,
as we have seen that they are carried, for untold
generations.

THE CONTINUITY OF THE GERM-PLASM

This germ-plasm, which is the connecting link
between one generation and another, is passed on,
according to the prevalent idea, from parent to
offspring, generation after generation, subject
only to such modifications as may from time to
time be imposed through environing influences.

The physical mechanism that underlies this
transfer we shall have occasion to examine in
another connection when we discuss at some
length the theories of heredity. For the moment
it is enough to reflect that as the offspring in each
successive generation spring from the substance
of the parent, the germ-plasm may be thought
of as a continuous stream uniting the remotest
ancestor of any given strain with the most recent
descendant.

[52]

A Mosaic Leaf

When a purple-leaved plum is hybridized with a
green-leaved plum, the hybrids of the first generation have
green leaves, but purple leaves reappear among the varying hybrids
oj the second generation. Occasionally, however, a cross between
purple-leaved and green-leaved varieties, where the varieties
lie near the limits oj affinity, results in a condition
that might be described as a mosaic, the leaves par-
taking oj the characteristics oj both ancestral
strains. This picture illustrates such a case.

LUTHER BURBANK

Every tree in the orchard, for example, car-
ries within its tissues a portion of protoplasmic
matter that has come down to it through an
almost infinite series of growths and divisions in
unbroken succession from the first tree that ever
developed on the earth — or, for that matter, from
a vast series of more primitive organisms that
were the progenitors of the first tree.

And while this stream of primordial proto-
plasm has been changed by an infinitesimal
quantity in each successive era, it has retained
even to the present the fundamental character-
istics that it had from the outset.

That such is the case seems little less than a
miracle; that an almost microscopical speck of
protoplasm which we term a pollen grain should
contain the potentialities of thousands of genera-
tions of ancestors, and should be able to transmit
them with such force that the seed growing from
the ovule fertilized by that pollen grain will
inevitably produce, let us say, an apple tree, not
a pear tree or a plum, is beyond comprehension.

Yet we know it to be true.

And so the plant hybridizer who consciously
merges two different protoplasmic streams when
he brings the pollen of one flower to the pistil of
another, participates in what must be considered
the most wonderful of all experiments.

[54]

PLANT AFFINITIES

He brings tokens out of an almost infinite past
to blend with the divergent tokens of another
ancestral stream no less ancient.

And it is not strange if he feels a certain
impulse of elation when he reflects that his con-
scious efforts have thus brought together ancestral
tendencies that have long been separated and
that now will appear in new combinations-
stimulating such interplay of life-forces as
may bring into being plant forms that may be
described, without violence to the use of words,
as new creations.

—That the intimate record of
cousinship, in all its grades,
should be permanently graven
in the protoplasm of every
living thing, is a thought-com-
pelling biological revelation.

A Shirley Poppy — Showing Reproductive Organs

The petals oj a flower are designed to attract insects. The

essential organs are the pollen-bearing stamens and the pistil

joining the ovule at the center oj the flower. This picture shows the

large number of stamens of the poppy, each with a terminal

anther, bearing pollen, growing in a circle about the pistil

with its curiously rounded end, called a stigma,

designed to receive the pollen. The office

oj the insect is to transfer pollen

from the stamens of one flower

to the pistil of another.

PRACTICAL POLLENATION

A SURVEY OF WORKING METHODS

ONCE upon a time — it may have been
about the year five million B. C. — a plant
imbued with nascent wisdom made a
tacit compact with a fellow creature of the world at
large that was fraught with strange and fateful
meanings for races of beings yet unborn.

The fellow creature in question was at that
time probably the most highly developed citizen
of the world, although in modern terminology he
would be termed "merely an insect." The com-
pact the plant made with him was to the effect
that one should manufacture sweet nectar and
freely supply it as food; and that the other in
return should carry the fructifying pollen grains
from flower to flower.

Doubtless no more important compact was
ever entered into in the history of animate crea-
tion before or since.

[VOLUME III — CHAPTER III]

LUTHER BURBANK

For out of this compact grew the rivalry that
stimulated development and made possible the
evolution of the whole race of plants that bear
beautiful flowers and exhale sweet perfumes. But
for this eventful alliance, there would never have
developed in the world a conspicuously colored
or a scented flower of any kind.

And it requires no argument to show that
a world without beautiful and sweet-scented
flowers would be a world robbed of a large share
of its attractions as an abiding place.

But that is not all. The alliance between insect
and flower did not merely suffice to give us things
of beauty. It bespoke utility as well. It made
possible the bringing together of germ-plasms
from plants growing far apart, thus insuring virile
and variant strains; and this determined in large
measure the amount and direction of the evolu-
tion of the highest orders of plants.

For it must be observed that, with rare excep-
tions, the higher plants are precisely those that
long ago entered into this cooperative scheme
whereby they trusted their fate absolutely to the
insects. They hazarded much — for if anything
should lead to the destruction of a few insect
races, entire orders of plants would suffer race
suicide. But if they risked much, they also
profited much; for the cross-poll enizing effected

[58]

The Stigma of a Poppy, Greatly Enlarged

The stigma of the flower may be variously modified to facilitate
reception of the pollen. This picture shows the curious arrange-
ment in the case of a poppy. The pollen grains deposited on this
stigmatic surface send out little tubes that penetrate the stigma
and ultimately make their way to the ovule or seed case,
carrying the nucleus that unites with the nuclues
of the egg cell, thus effecting fertilization.
Each egg cell is fertilized by a
single pollen nucleus.

LUTHER BURBANK

by the insects afforded the constant stimulus to
variation that underlies all evolution, and enabled
the plants that entered into the coalition presently
to outstrip their fellows.

Wherever you find a tribe of plants that shows
great diversity of form, large numbers of species,
and ready adaptability to improvement, you will
as a rule find a tribe of so-called "entomophilous,"
or insect-loving flowers, dependent upon the
winged messengers for the consummation of their
matings.

Vast responsibilities then were implied in this
coalition of the plants and the insects; but the
results have justified the hazard.

PLANTS THAT DID NOT JOIN THE UNION

We shall presently see illustrated in detail
the curious adaptations of form and color and
structure to which the plants of various species
were led in their rivalry to secure the good graces
of the insects and thus to make sure of perpet-
uating their species.

Every blossom of the entire orchard, every
flower of the garden, and with a few exceptions
all of the vegetables under cultivation furnish
illustrations in point. But it should be recalled
that there are large numbers of plants of a lower
order that from the outset refused to enter into
the coalition, and that even to this day have

[60]

PRACTICAL POLLENATION

declared themselves independent of the plant-
insect union.

Plants of this non-union clan are the entire
races of lowly mosses and lichens; a goodly num-
ber of aquatic forms that maintain the appearance
and manner of their remote ancestors; and the
familiar tribe of ferns; and some of the trees
which depend mainly upon the wind.

All of these, and a large company of forms
less familiar to the amateur, have obstinately
retained throughout the ages the primeval habit of
propagating their kind not with immobile pollen
grains but with the aid of self-moving germ-cells.
These motile germ-cells, of microscopic size, find
their way through the water — supplied in case of
land plants by a film of rain or of dew — from
one plant to another, and effect cross-fertilization
without calling in the aid of any allies. They do
not need to attract insects, and so they have not
adopted the system of advertising through the
development of large and showy blossoms and
nectar cups to which the members of the plant-
insect alliance are obliged to resort.

But if the lowly plants thus maintained their
independence, they have done so at a very great
sacrifice.

They are not more independent than they are
unprogressive ; and indeed they are unprogressive

[61]

Pollen-Bearing Pumpkin Blossom

Many plants bear pollen and ovule on separate

blossoms, so that self-fertilization is impossible. They are

said to be dioecious. This picture shows a pumpkin blossom with

the modified and coalesced stamens at its center bearing a

quantity of pollen. The insects in visiting the blossom

carry the pollen on their bodies or feet and

transfer it to other flowers.

Seed-Bearing Pumpkin Blossom

This blossom is the mate oj the one shown on the

opposite page. The stigma to receive the pollen occupies the

same position that is occupied by the pollen-bearer in the other flower.

The bulbous growth at the base of the flower is the ovary,

or seed case, which, if the flower is fertilized,

will develop into a pumpkin.

LUTHER BURBANK

precisely because of their independence. The
method of cross-fertilization that they have
adopted does indeed enable some of them to
blend the strains of different individual plants;
but in every instance the parents must be growing
in the immediate vicinity of each other.

Except by the accidental and most unusual
transfer of a plant through the agency of a
passing animal, there is hardly the remotest
chance of effecting cross-fertilization between
individual mosses or lichens or ferns growing in
widely separated regions.

But we have already seen that it is precisely
this blending of traits brought from parents
growing under different environing conditions
that is chiefly responsible for making plants vary
and furnishing the materials for evolutionary
progress. So it goes without saying that the plants
that are restricted, in the choice of possible mates,
to individuals growing under the same conditions
to which they themselves are subjected, cannot
expect to change rapidly and therefore do not
evolve in any such ratio as plants having the
other habit.

And in point of fact we find that the plants that
retain this primitive custom of fertilization with
the aid of motile germ cells, acting quite inde-
pendently of insect or wind, are plants of a

[64]

Cross-Section oj a Cactus Blossom

This is what is called a perfect flower — that is to say one that
has both stamens and pistil. The stamens are grouped in a circle
about the pistil, as in case of the poppy, this being the typical arrange-
ment. The picture shows the seed case or ovary at the base of the
pistil. Each ovule must receive the nucleus of a pollen grain
or it will not develop. Where the stamens are thus clustered
about the pistil, cross-fertilization is usually prevented by
the maturing of the two sets of organs at different periods.

LUTHER BURBANK

low order of development, showing relatively
little diversity of form and small capacity for
adaptation.

The most conspicuous of them with which the
ordinary observer is familiar, namely the ferns,
bear a striking resemblance in contour to plants
of the remote Carboniferous Era, traces of which
have been preserved in the coal beds. And there
can be no doubt that this persistence of the
primitive form has been largely due to the
special method of fertilization which the ferns
have retained.

If it be permitted to carry personification one
stage farther, we might say that the ancestors
of the ferns belonged to a conservative family,
jealous of its independence, and unwilling to enter
into outside alliances.

And the penalty of conservatism here, as so
often in the range of human experience, has been
racial stasis.

PLANTS THAT HAVE LEFT THE UNION

It would appear, however, that there are
certain races of plants that were once members
of the plant-insect alliance but which are now no
longer in the union.

These apostates include two quite different
tribes of plants.

On one hand there are numerous gigantic

[66]

PRACTICAL POLLENATION

trees that no longer depend upon insects for the
fertilization of their flowers.

On the other hand there are little cowering
plant-waifs that nestle close to the earth and
which, in quite a different manner, also assert
their independence.

The trees that have thus revoked the treaty of
alliance include such familiar forms as the pine,
the oak and the walnut.

These trees, and a goodly number of their
fellows, long ago declared against further coop-
eration with the insect, and adopted the method
of producing large quantities of pollen and
scattering it in the air to be carried by the wind
to the pistillate flowers, which in some cases grow
on neighboring branches and in other cases on
quite different trees.

The method is in one sense wasteful, inasmuch
as it involves the production of vast quantities of
pollen, only an infinitesimal portion of which will
ever come in contact with a receptive pistil. And
of course the production of this pollen must draw
heavily on the energies of the living substance of
the tree.

But on the other hand the tree that thus
depends upon the wind rather than upon the
insects is under no necessity to develop large
and conspicuously painted flowers. Nor need it

[67]

Two Gourd Blossoms to be Pollenated

The Gourd belongs to the same family as the pump-
kin, and, like that plant, bears the staminate and pistillate
flowers separately. This arrangement makes it very easy to effect
hybridization. Gourds and other squashes are cross-fertilized
so readily that different species must be grown far
apart if the strains are to be kept pure.

Pollenating the Gourd Blossoms

To effect fertilization, nothing more is necessary

than to pluck a staminate flower, pulling away its corolla,

to expose the pollen-bearing surface, and to insert this in the pistillate

flower, gently dusting the stigma with pollen. The facility

with which this may be effected makes the members

of this family very attractive to the

amateur experimenter.

LUTHER BURBANK

produce nectar to feed the insect allies, since
these have been renounced. And it may very well
chance that the saving of energy thus effected
more than counterbalances the waste through
excessive pollen production.

At all events the plants that have adopted this
system of pollenizing give evidence that their plan
is not a bad one in the very fact of their extreme
abundance.

Moreover the "wind-loving" or "anemophilous"
plants, as the botanist terms them, have not only
produced a great variety of species and vast
numbers of individuals, making up the bulk of
our forests, but the individuals themselves are of
such virility of constitution as to attain gigantic
size. Indeed a moment's consideration makes it
clear that the plants that had depended on the
wind rather than on insects for fertilization are
quite in a class by themselves in the matter of
size, inasmuch as they constitute the bulk of our
forest trees.

This relation between size and habit of
spreading the pollen broadcast on the winds
cannot be altogether accidental.

But whether the trees grew large because they
had given up the alliance with the insects, or
whether they gave up the alliance because they
were growing large, it would be hard to say.

[70]

PRACTICAL POLLENATION

We know that, in the main, insects tend to
keep near the surface of the earth, and it may
be that the plants that tended to grow very tall
were relatively neglected by the insect messengers.
But on the other hand, there are insects that haunt
the highest trees, and we can hardly doubt that
had even the tallest of plants desired to retain the
services of insect messengers, races of these would
have been developed that would have proved
equal to the most exacting demands.

What seems on the whole most probable, then,
is that the trees have changed their allegiance
from insect messengers to wind because of the
very nature of the conditions under which they
grew.

By raising their heads high and higher into the
air they obviously put themselves more in contact
with the wind and thus make it increasingly
possible to spread their pollen broadcast across
wide stretches of territory.

As a matter of fact we know that the pollen
of pine trees in particular may be carried almost
in clouds for scores and even hundreds and
hundreds of miles.

So there is every opportunity for the cross-
fertilization of individual trees growing in widely
separated territories; and there is therefore no
restriction put upon the possibilities of progress

[71]

LUTHER BURBANK

and evolution for these large-growing plants in
penalty for their renunciation of the services of
insect messengers.

The case of the trees, then, simply illustrates
the fact that there may be more than one way
to effect a given purpose, and that a change of
method may be no barrier to progress, even
though the abandoned method still remains an
admirable one for a vast coterie of organisms of
slightly different habit.

SELF-FERTILIZED PLANTS

But the case of the other company of plants
that have back-slidden from the insect alliance
is altogether different.

The plants in question do not make up any
great conspicuous tribe, comparable to the forest
trees, but are a miscellaneous company of
lowly vegetables of unrelated families. Familiar
examples are the wheat of the fields, peas and
beans in our garden, and a certain number of
the more obscure species of violets.

The jewel weed, the fennel, the rue, and the
nettle, are other somewhat less familiar yet not
uncommon tribes of plants whose flowers are
habitually self-fertilized.

There can be no question that these plants are
the descendants of tribes that were at one time
members of the plant-insect union. The fact that

[72]

Strawberry Blossom Ready /or Pollenating

Some varieties of strawberries bear perfect flowers
as illustrated in this specimen, and others have blossoms that
bear the pistils separately. It is necessary, in cultivating the straw-
berry, to bear this in mind, and ij a pistillate variety is planted
there must be pollen-bearers in the neighboring rows, otherwise
there would be no crop oj berries. The bees are depended
on to effect the transfer of pollen. In the perfect
flowers, the stamens and pistils mature at
different periods, to guard against
self -fertilization.

LUTHER BURBANK

most of them retain more or less conspicuous
flowers proves this beyond question. In the case
of the wheat, which might be thought a possible
exception, there is the evidence of certain species
of wild wheat, growing to this day in Palestine,
which have only partially renounced allegiance
to the insects, still putting forth flowers that on
occasion may be cross-fertilized with their aid
or with that of the wind.

Just why these various plants of different
families have departed from the custom that has
served their fellows so well, would be interesting
matter for conjecture.

Perhaps the most plausible suggestion is that
the ancestors of the plants that now have
closed flowers and thus depend exclusively upon
cross-fertilization had fallen on evil days in which
there was a dearth of insect messengers in the
regions they inhabited.

The story of the starved martins, told in an
earlier chapter, furnishes a striking illustration of
the fact that insects that ordinarily are abundant
may in any given season fail to put in their
appearance.

And even if the insects themselves are abun-
dant, the weather conditions, in a given season,
may be such as to make it almost impossible for
them to carry out their bargain by transferring

[74]

.s p| a n*& 2-.

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LUTHER BURBANK

pollen from flower to flower. Every orchardist
knows that a protracted rainfall just at the time
when his apple, pear or plum trees are in bloom,
may prevent the bees from visiting the flowers;
and in such case, as is only too well known, there
will be a partial, or no crop that season.

With trees and other perennial plants it is
not matter of absolutely vital importance that
there should be a crop of seeds produced each
season.

Failing progeny this year, next year or the
year after will answer, in the case of a plant
which grows on a permanent stalk or from roots
outlast the winter.

But the case of the annual plant is altogether
different.

Should such a plant fail for a single season
to produce seed, its entire race would vanish
instantly from the earth.

That thought is rather startling when presented
thus tangibly.

Yet its truth is almost axiomatic. As a rule,
the entire seed crop of an annual plant in a state
of nature, either germinates or decays the ensuing
season after its production. And it is absolutely
incumbent on the plants that grow from this seed
to produce in turn a store of seed that will carry
on the racial stock.

[76]

PRACTICAL POLLENATION

So it is not strange that a plant that is
thus perennially threatened with destruction
should adopt exceptional measures to ensure the
fertilization of its flowers.

Very often it may have happened that certain
individual flowers that chanced to be self -fertilized
were instrumental in saving the life of a species
that otherwise would have been exterminated.
And as, through the operation of heredity,
the offspring of these flowers would tend to
reproduce the self-fertilizing habit of their parent,
the surviving representatives of the species might
thus come to constitute a tribe in which the
habit of bearing self-fertilized flowers was the
prevailing custom.

And thus it is, perhaps, that the method of
reproduction followed by the wheat in our fields
and the peas and beans in our gardens may be
accounted for.

Yet the fact that certain of these self-fertilized
flowers, as for example the violet, retain the
custom of putting forth showy flowers even though
these for the most part are seedless, shows how
powerful is the hold of remoter heredity, and
how persistently the plant clings to a custom to
which its ancestors owed their racial development.
Moreover, it has been observed that the violet,
when transplanted to a sunny spot and made

[77]

LUTHER BURBANK

accessible to insects, may resume the custom of
growing seeds in its conspicuous flowers, whereas
hitherto it had produced them only in the small
inconspicuous bud-like flowers at its base which
never open.

SCHEMES TO ENSURE POLLENATION

It is curious to observe how insistent is the
inherent demand for fertilization of the flower,
and how even flowers that openly advertise for the
insects may strive to provide for self-fertilization
in the event that their call remains unanswered
and in vain.

The common barberry (Herberts vulgaris) for
example, opens and exposes its pollen-bearers
only during the bright hours of a cloudless day.
But in case an insect fails to visit it, provision is
made that will ensure self-fertilization; for in
due course the stamens dart forward and sprinkle
their pollen over the pistil.

In the case of the fennel flower of France,
described elsewhere, which does not open at all,
the pistils bend forward when they are ripened,
and after taking the pollen from the stamens,
straighten up again.

With the rue, the arrangement is curiously
complex and machine-like. Of the several
stamens, each in turn bestows its pollen on the
pistil at their common center. It has been

[78]

Balloon Berry Blossom

Such a flower as this is rather troublesome for the

pollenizer, as its cluster oj stamens must be removed, to make

sure that self-fertilization does not occur. This may be effected with

a small pair oj pincers. The operation is not difficult, but it

requires time. Of course care must be taken not to

injure the stigma, which is to be fertilized

with pollen Jrom another flower.

LUTHER BURBANK

observed that the stamens advance alternately,
numbers one, three, and five in turn; numbers
two, four, and six following in succession, as if
the entire mechanism were actuated by clock
work.

But these and sundry other ingenious mech-
anisms for self-fertilization after all only evidence
the resourcefulness of a plant in its struggle for
self-preservation.

It is better that a flower should be self-
pollenized than that it should not be pollenized
at all. But the process is in no wise comparable,
in its value for the race, to the more usual process
of cross-fertilization.

The self-fertilized plant develops fixity of race.
It lacks the needed stimulus of the blending of
different racial strains. It will produce few
varieties, thus giving little opportunity for the
operation of natural selection.

In a word, such a plant is really marked for
ultimate extinction, unless, as in the case of the
wheat, man steps in to give it the refuge of
artificial selection.

It may well be doubted whether the existing
races of cultivated wheat could perpetuate their
species, if put upon their own resources in
competition with wild plants, for a dozen or two
dozen years.

[80]

Balloon Berry Bush After Pollenation

Here small paper bags have been tied loosely over

the flowers that have been cross-fertilized. Mr. Burbank does

not usually find it necessary to resort to this expedient, for if the stigma.

oj a flower is entirely covered with pollen, there is little danger

oj subsequent contamination with oilier pollen. To make

assurance doubly sure, however, the paper bags

may be used, particularly by the amateur

who operates on a small scale.

LUTHER BURBANK

The habit of self-fertilization may preserve
for a certain number of generations a plant
that would otherwise have been completely
exterminated; but at best it marks a stage of
degeneration and decline. The plant that follows
it is in a sense retracing its steps down the ladder
of evolution by which its ancestors have made
ascent.

And so it is not surprising to find that the vast
majority of the useful plants of orchard and
garden have kept up the traditional alliance with
the insects to which they owe the multiplicity
of their specific forms and the virility of the
individual members of their organization.
THE WISEST OF PLANTS

It is flowers of the great brotherhood of insect-
lovers, then, that chiefly claim the attention of
the plant experimenter, because these are the
ones that make up the chief census of orchard
and garden.

As a matter of course it is plants of this
fraternity that are of interest to the amateur,
because, generally speaking, it is these alone that
put forth blossoms that please the eye.

Whoever is interested to undertake experi-
ments in plant breeding must then, familiarize
himself with the mechanisms by which the plant
makes known its appeal to the insect and those

[82]

Complete Kit of Pollenizing Tools

This shows all the apparatus required Jor the most elaborate series of ex-
periments in cross-fertilization. The scapel is used sometimes to cut
across unopened blossoms — Jor example, apple blossoms — in such a way
as to remove the pollen-bearing anthers all at once. Where the Jorm oj
the flower does not permit this, the pincers are used to pluck out the
stamens. The watch crystal is used to collect pollen, which is trans-
ferred to the stigma oj another flower either with the finger tip or with a
camel's hair brush. The other implements are required exceptionally
to manipulate a flower oj peculiar Jorm. The magnijying glasses are
needed only with very small flowers. The use oj the paper bags is
illustrated on page 81. The cardboard labels are to record the experiment.

LUTHER BURBANK

through which the perpetuation of its kind is
effected; the mechanisms, that is to say, of the
typical flower.

As we come to study flowers in detail, it
will appear that among those dependent upon
insect-fertilizers, no less than among the wind-
fertilized, there are individuals that bear the
essential organs of the flower in separate blossoms.
Reference was made to this in the case of our
hybridizing experiment with a certain species of
dewberry, and we shall see other illustrations of
it from time to time.

But the major part of the most familiar
cultivated plants, including all the conspicuous
fruit trees of our orchards, bear flowers each of
which contains within the same blossom both the
staminate and the pistillate organs.

Ordinarily it is the function of the bee to
carry pollen from one blossom to the pistil of
another. But on occasion even these flowers may
be self-fertilized. Thus it may be said that the
most important, from a human standpoint, among
the existing plants have adopted a compromise,
in which cross-fertilization is the rule, yet which
makes possible self-fertilization in case, under the
stress of circumstances, cross-fertilization should
fail to take place.

Doubtless on the whole this was the best course

[84]

PRACTICAL POLLENATION

of all. The plants that adopted it might be said
to be the wisest of their race.

THE TYPICAL FLOWER

What may be regarded as the typical or perfect
flower, then, is one that contains both pollen-
bearing and pollen-receiving parts, surrounded
by the conspicuous insect signal that we term the
corolla; and having also a less conspicuous outer
shield termed a calyx.

The calyx is the original shield about the
flower bud, and its function is over when the
flower opens.

The botanist ordinarily speaks of the calyx as
a modified leaf. He refers to the petals of the
corolla as being also modified leaves or enlarged
and beautified modifications of the calyx. He
thinks of the stamens and the pistil as modified
petals; and he justifies this estimate by showing
that under cultivation it is often possible to trans-
form these essential organs into petals.

Thus, for example, are produced such double
flowers as the cultivated rose and the chrysan-
themum. To the human eye, these are things
of beauty but from the standpoint of plant
economy they must be regarded as travesties of
flowers, since they are far less able and often
wholly incapable of producing seed.

But it is perhaps a somewhat more philo-

[85]

Pollen-Bearing Grape

The members of the grape family, like the strawberry,

differ as to the character oj their flowers. Some plants bear

perfect blossoms, others are staminate with at most a rudimentary

ovary. The plant thus occupies an intermediate position betiveen

those plants that all bear perfect flowers and those that

always bear the stamens and pistils on separate

blossoms. The various arrangements suggest

the need of cross -fertilization in

the economy of plant life.

PRACTICAL POLLENATION

sophical view of the flower to consider it as a
mechanism developed about the all-essential cen-
tral organ, the pistil.

This, the female organ of the plant, consists,
in the developed form, of a basal structure, the
ovary, containing the ovules or embryo seeds, and
a more or less protuberant style at the end of
which is the stigma that receives the fertilizing
pollen.

Considered as to its origin, the pistil is in effect
a modified bud. Everyone is aware that individual
buds of a plant may have the property of being
able to reproduce the entire plant. The pistil is a
modified bud each embryo seed of which, when
fertilized, has the same potentiality.

By the most wonderful miracle of the organic
world, this infinitesimal structure is enabled to
epitomize all the possibilities of a future plant, of
predetermined size and form and habit.

It differs from the bud from which it is
developed chiefly in that it requires to be fertilized
by union with a pollen cell, before it is capable of
taking on development; and in the further very
essential fact that when mature it may be cast off
from its original moorings and carried to any
distance, thus in a way making amends for the
limitations put upon vegetables by their inca-
pacity for locomotion.

[87]

LUTHER BURBANK

The stamens that normally grow in a circle
about the central pistil develop at their ends
anthers that produce, usually in relatively large
quantities, pollen grains of exceedingly minute
size. And each pollen grain contains, somewhat
as does each ovule, all the hereditary potentialities
of the entire plant. The pollen grain cannot,
indeed, be made to develop into a plant; but its
union with the ovule is essential to the develop-
ment of that organism, and it is certain that the
pollen grain, despite its infinitesimal size, brings
to the union factors that represent its parent plant
effectively and in full measure.

It would be unbelievable, if we did not know
it to be true, that a fleck of matter of scarcely
more than microscopic size should contain the
potentialities of a mammoth tree, and should pre-
determine the details of structure of a future tree
even to its remotest leaf and to the finest details
of its flowers and fruit. But that the pollen grain
actually has these potentialities has been demon-
strated thousands of times over by the plant
experimenter.

Any amateur who wishes to test the matter
may do so, to his complete satisfaction, by making
the simplest experiment in cross-pollenizing and
watching the growth of the hybrid seedlings his
work brings forth.

[88]

Giant Artichoke in Blossom

The artichoke belongs to the family of Composites,

in which numerous blossoms are grouped together to form a

head with a single floral envelope. The daisy and the sunflower furnish

familiar examples of this arrangement. The artichoke for eating

is plucked before the blossoms are mature. If allowed to

reach the stage shown in this picture, it is inedible. Mr.

Burbank has developed new varieties of artichoke,

the heads of which are of gigantic size.

LUTHER BURBANK

The pollen grain effects union with the ovule
by sending out a thread-like filament of proto-
plasm, like a tiny root, which penetrates the
stigmatic surface, passes down along through the
style, and carries the nucleus of the pollen grain
to the nucleus of an ovule. When the two
nuclei come in contact, fertilization has been
accomplished.

When pistil and the stamens have been con-
sidered, we are through with the really essential
mechanisms of the flower.

From the human standpoint, of course, chief
interest centers in the corolla with its wide-
spreading petals of varied colors. To the plant
itself this structure is in a sense essential, inas-
much as it supplies the visible signal that attracts
the attention of the insect. But beyond this it has
no share in the process of fecundation. We shall
have occasion to consider the form and structure
of this showy portion of the flower in a multitude
of individual cases, and to observe how it may be
modified by process of selection, but from the
present standpoint it does not call for further
consideration.

From the standpoint of the pollenizer, the
stamens with their pollen-bearing anthers and the
receptive pistil — with or without a stigma at its
tip but always having one or more ovules in the

[90]

PRACTICAL POLLENATION

egg-case at its base — are the organs that claim
exclusive attention.

HAND POLLENIZING

The essence of pollenizing is merely the
transfer of pollen from the stamen of one flower
to the stigmatic surface at the end of the pistil
of another.

This is the work that is ordinarily accomplished
by the insect. It is all that the plant experimenter
accomplishes when he wishes to effect the crossing
of different plants of the same species or the
wider crossing, commonly called hybridizing, of
different species.

There is nothing occult in the practice of the
bee or in the imitation of his work as practiced
by the hand of the pollenizer.

What is accomplished in each case is the
purely mechanical transfer of a certain number
of minute pollen grains from one place to another.
Beyond that, everything depends on the vital
activities of the plant tissues themselves.

We shall have occasion in another chapter to
deal somewhat at length with specific methods
that are necessary to effect cross-pollenizing in the
case of sundry types of flowers that have devel-
oped blossoms curiously modified as to form or
details of structure. But the general processes of
hand pollenizing, as they apply to the chief

[91]

Pollen-Bearing Chestnut Blossom

The chestnut bears its pollen and its ovules separately.

It depends largely on the wind to transfer the pollen, and hence

does not develop a conspicuous floral envelope to attract insects. But

the massed blossoms, in spite of their small individual size,

ore conspicuous, as this picture shows. The

pollen is produced in relatively

enormous quantities.

Stigmatic Chestnut Blossoms

Hand pollenizing of the chestnut is effected with the

greatest facility, nothing more being required than to pluck a

pollen-bearing branch, like that shown on the opposite page, and

dust it lightly against such a stigmatic branch as this. Mr.

Burbank has produced remarkable results by hybridizing

chestnuts Jrom Japan with European and American

species. Some hybrids are immune to the

Jungus that destroys the American chestnut.

LUTHER BURBANK

flowers of the orchard and garden, may be stated
in a few words.

The essential thing is to secure a certain
quantity of pollen, usually by shaking it from
the flower on a watch-crystal or other small
receptacle, and to transfer this pollen to the
receptive pistil of another flower either with the
finger tip — which furnishes in general the most
useful piece of apparatus — or with a camel's hair
brush.

It is desirable to cover the receptive portion
(stigma) of the pistil fully with pollen, partly
to ensure complete fertilization, and partly to
prevent the vitiation of the experiment through
possible subsequent deposits of pollen from
another source.

If the flower to be fertilized has stamens of
its own, these should be removed before they are
fully ripe — which is often a few hours, or a day
before the foreign pollen should be applied. This
removal of the stamens may usually be done
with a pair of small pincers. In case of flowers
that have short pistils — the cherry, apple, and
other orchard fruits being good examples — the
unopened flower bud may be cut around at about
the middle, with a thin-bladed knife, the anthers
being thus excised at a single stroke. * With other
flowers the mechanical details vary, of course; but

[94]

Corn SelJ-Pollenated and Crossed With Teosinte

The upper ear is an ordinary ear of corn, presenting
no marked peculiarities. Thz lower ear was developed by
pollemzing the corn silk with pollen from the primitive type of corn
called teosinte, which is illustrated on earlier pages of the present
volume. The influence of the pollen-parent is clearly
shown in the modified form of the kernels. With '
most plants the pollen does not directly
effect the fruit, but corn is an excep-
tion in this regard.

LUTHER BURBANK

the process is seldom complicated. It calls for
common sense rather than for great ingenuity.

So-called composite flowers, however, require
special treatment. The daisy and the sunflower
are familiar examples. Here the true flowers are
very small and grouped in masses. Individual
treatment is usually out of the question. The
best method is to wash away the pollen with a
carefully directed stream of water from a garden
hose, or by spurting water from the mouth; after
which the head of the pollenizing flower is rubbed
rather vigorously against the one just de-pollen-
ated, thus effecting fertilization en masse.

In exceptional cases it may be desirable also
to cover the fertilized flower with a paper bag
to prevent the visits of insects; but in practicing
pollenation on a large scale this may usually be
omitted.

If the stigma has been satisfactorily covered
with pollen, it will present no exposed surface for
the reception of other pollen grains.

Pending the more detailed discussion of the
specific methods of pollenizing adapted to par-
ticular flowers, I would give an all-compassing
rule which, in itself, will serve as a sufficient
guide to the experimenter who has clearly in
mind the principles involved in the process of
cross-pollenation.

[96]

Corn Insufficiently Pollenated

Each individual ovule must be fertilized with the

nucleus of a pollen grain. The so-called silk of the corn

consists oj thread-like pistils, each of which leads to an ovule. The

pollen, produced in the tassel, sifts through the air in great

quantities, but sometimes it fails to reach all the threads

of the corn silk. In that case a defective ear is

produced as shown in this picture.

LUTHER BURBANK

The rule is simply this: Seek Nature's plan
and follow it.

In other words, take a lesson from the bees,
and pollenize the flowers somewhat as they do.
Bear in mind the essentials of the process,
which are the same for every flower. Study the
mechanism of each new flower and adapt your
precise method to the needs of the individual case.
It does not matter just how the pollen reaches the
reception stigma, provided it does reach it.

A very short course of practice will give you
the knack of cross-pollenizing, and enable you to
enter on a course of experiments that will lead to
surprising, fascinating and perhaps far-reaching
results — results which may prove to be of time
wide and world wide significance.

— The ferns belong to a conser-
vative family; and the penalty
of conservatism, whether in
plants or in human beings,
has always been racial stasis.

QUANTITY PRODUCTION

ON SEEDLINGS
AND THEIR CARE

THE word "evolution" chances to have nine
letters. Suppose that these letters were
penciled on nine blocks of wood that are
otherwise identical, and these little blocks were
put in a bag and mixed together. Suppose then
that you were asked to put your hand in the bag
and bring forth one block after another, placing
them in sequence as you brought them from the
bag.

What probability is there, do you think, that
your blindfold selection of the blocks would
result in bringing them out in such sequence as to
spell the word "evolution"?

A mathematician could doubtless figure out
the exact probabilities, but you need not be a
mathematician to realize that the chances are
almost infinitely against you.

Now I think I am right in saying that the

[VOLUME III — CHAPTER IV]

LUTHER BURBANK

plant developer who expects to find a considerable
number — let us say nine — of particular qualities
of any given flower or fruit or vegetable combined
in just the desired proportion in any single
seedling selected at random, stands about the
same chance of having his expectations gratified
that you have of spelling out the word "evolution"
correctly with blocks drawn at random.

But it is obvious that your chance of successful
drawing of the blocks would increase in proportion
as the number of attempts you are permitted to
make increases.

So would the plant experimenter's chance of
finding several desired qualities of his fruit or
flower combined in just the right proportion
increase somewhat in proportion to the number
of seedlings among which he can select.

Yet I suppose the mathematician would assure
us that the number of attempts you must make
with the blocks before you could hope, according
to the theory of chances, to bring out all the letters
in just the right sequence would be so large as to
tax your patience beyond endurance and I can
testify that the same thing holds true with regard
to the experiment of the plant developer. Though
he had thousands of seedlings among which to
choose he is not likely to find any one in a given
fraternity that fully meets his ideal.

[100]

5' 3

LUTHfiR BURBANK

; : : But if in making your experiment of choosing
tKe lettered blocks you were permitted to retain
the blocks bearing the letter "E" when you
chanced to draw it first; and if then you were
permitted to retain the letter "V" when that was
first drawn from the remaining group of eight
blocks; and so in sequence with "O" and "L" and
the rest — it is obvious that each new test would
find you with a smaller number of letters from
which to select, and hence with an increasing
probability of successful selection.

When, finally, there remained only two letters
in the bag, your chance of securing the right one
in the first draw would obviously be an even one.
And when only the final "N" remains, you could
make no mistake — your selection of the right
letter then becomes a certainty.

Now I make this illustration because I think
it has peculiar application to the case of the plant
developer. His method is not unlike the method
of selection just suggested. As the result of his
first hybridizations, he does not dare to hope that
he will secure the exact combination of qualities
he would like to see aggregated in his ideal fruit
or flower. But by having a large number of
seedlings from which to select he may reasonably
hope to secure one that will present some one at
least of the desired qualities in superlative degree.

[102]

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This selected seedling he may nurture and use as
part of his equipment for further experiment just
as you retained the letter "E" as marking the
beginning of your success in spelling the word
"evolution."

And as the plant developer continues his
experiment with successive hybridizings and
successive selections, he will be able in later
generations to find individual seedlings that
combine successively more and more of the
qualities he is seeking. When, finally, he reaches
the stage where the parent forms have between
them all the desired qualities in superlative
degree, he is somewhat in the position that you
were in when only two of your lettered blocks
remained in the bag. There is at least an even
chance that he will find among his seedlings of
the next generation one that will approximate his
ideal, even though the number from which he
selects is far smaller than the earlier groups.

Thus by advancing step by step and using
the ground gained as a new starting point the
experimenter attains his end with comparative
celerity, even though there would have been
scarcely more chance of attaining that end with
a single experiment than you would have had of
spelling out the word "evolution" at a single
series.

[104]

QUANTITY PRODUCTION

But it must be fairly remembered that the
probability of success is enhanced if at any of
the earlier stages of the work you have
opportunity to select the best plant among a
large group instead of being restricted in choice
to a few individuals; just as the chance of
securing the block you seek in each successive
drawing increases with the number of tests you
are permitted.

And in point of fact, this, or something like
this, is the actual method in which the
experiments of the plant developer are carried
out, whenever he is attempting to construct a new
fruit or flower or vegetable having a number of
specified or clearly imagined qualities. In such
a case, the wise experimenter does not hope to
secure ideal results with a single hybridization;
he seeks to group desired qualities of his flower
or fruit together through successive crossings and
selections. Keeping one supreme quality in mind
and perhaps two or three others in the immediate
background, he makes sure of first one and
then another of these qualities, adding to them
by successive crossings and selections and thus
although advancing, as it were by indirection, and
at first seeming to advance but slowly he may
ultimately work with increasing certainty and
approach his goal somewhat rapidly.

[105]

Germinating Seeds in Damp Cloth

Seeds of various kinds, arranged in loose rows as
here shown, may be rolled in a damp cloth and thus germinated
preparatory to planting. This is one of the numerous shortcuts
that Mr. Burbank practices. The method is some-
times used merely to test the viability of
seeds from different lots.

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Germinated in Damp Cloth

This shows the method illustrated on the opposite

page, at a later stage. The four different groups of seeds

have been germinated in the same roll of cloth, without mixing, and

they are now ready to be transferred to the soil,

either in the greenhouse or in

the field.

LUTHER BURBANK

For example, our first cross, say in the case
of a prune, may be made between two varieties
that both show a fair quality of fruit. Careful
attention to the result will guide us in the
matter of the next experimental crossing. We
soon discover which qualities are prepotent, and
which tend to remain latent, and by selecting only
individuals that show a tendency to vary in the
desired direction, we introduce an element of
direction into the experiment.

I am accustomed to speak of this as "momen-
tum of variation." We do not always know why
a certain plant tends to vary in a given direction,
but we may observe the fact, and the wise experi-
menter is always on the lookout for this tendency,
and ready to avail himself of the advantages it
offers. Technical workers sometimes give the
name "orthogenesis" to this tendency to vary in
a certain direction, which I speak of as the plant's
"momentum."

Whatever aid we may gain in this way, how-
ever, the manner of our advance is often devious.

In fact, it is very likely to be somewhat
comparable to the progress of a sailing ship which
tacks this way and that, and which at times may
seem to be progressing in the wrong direction, yet
which in the end forges ahead.

Take by way of illustration the case of our

[108]

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Pumpkin Seeds Germinated in Wet Newspaper

Sometimes Mr. Burbank employs a piece oj

newspaper instead of a cloth to germinate seeds, merely

wrapping the seeds loosely in the moistened paper. The efficacy oj

the method is demonstrated in this picture. Seeds thus

germinated will make rapid growth when

transferred to the soil.

LUTHER BURBANK

stoneless plum. We discover soon that the stone
seed is prepotent or dominant, and stonelessness
latent or recessive. So we must be prepared to
see the progeny of our first generation of hybrids
all produce stony fruit. But a knowledge of
the tendency of latent or recessive characters to
reappear in successive generations comes to our
aid, and we go on with the experiment with full
confidence, even though for the moment we seem
to be going backward rather than forward.

In due course the second generation of plums
appears with a number of stoneless specimens, the
latent character having come to the surface. But
these lack many of the good qualities that our
perfected fruit must have, and in order to breed
these qualities into the stock we must make a new
cross; and this will involve the breeding in again
of the tendency to bear stone fruit.

So in three generations we shall find ourselves,
as regards the essential quality of the stony seed,
somewhat further back than we were in the
beginning.

But, on the other hand, our third generation
fruit, even though it has a stony seed, has qualities
of flesh that its stoneless ancestor altogether
lacked; and in the fourth generation we shall be
prepared to find individual seedlings that bear
stoneless fruit of greatly improved quality.

[110]

QUANTITY PRODUCTION

In each successive generation, then, we are
dealing with better material — getting the chances
grouped, if you will.

WINNING AGAINST ODDS

But, in a sense, we are running counter to
the trend of heredity, because vastly the great
proportion of the ancestors of our plum were
bearers of stoned fruits. And so we must continue
re-shuffling and dealing over, as it were, and
watching results. We may lose in one generation
what we gained in the generation before as
regards the matter of stonelessness; even while
on the whole advancing toward the production of
a fruit of desired quality.

But just in proportion as our ideal calls for
the combination of numerous good qualities, does
the attainment of that ideal become difficult.

Even when, at let us say the fifth or sixth
generation, we interbreed individuals that have
the desired quality of stonelessness, we shall not
at once secure what is desired; because our
seedlings combine so many ancestral traits that
they will not breed true. Even though they are
all stoneless, there will be a great variation as
to other qualities, and it is only by dealing with
large numbers of seedlings that we can hope to
find one or two that will show the desired com-
bination of traits in high degree.

[in]

LUTHER BURBANK

Perhaps the comparison may be thought
somewhat whimsical; but I am led to make it
because I thought it might serve to suggest the
complexities and difficulties that attend a plant-
breeding experiment that involves the blending of
numerous desired characters.

And the lesson that I wish pre-eminently to
inculcate is this: You must make many experi-
ments at plant-breeding before you can hope to
secure the combination — -the sequence of qualities
—that you desire.

THE LOGIC OF QUANTITY PRODUCTION

Now note the application: Each individual
seedling of a hybrid strain represents a unique
combination of ancestral traits, and constitutes in
itself a new and unique experiment — equivalent
to an independent deal of the cards. So the prob-
ability of securing what we seek will be somewhat
proportionate to the number of seedlings.

This is particularly true in the case of such
variable plants as the fruit trees of our orchards.
The case is far simpler when we are dealing with
plants that vary little in their qualities, or where
we are breeding with only a single pair or two
pairs of unit qualities in mind — say "hardness"
of kernel and immunity to rust, as in Professor
Biffin's experiments with wheat; or good flavor
and whiteness as in my white blackberry.

[112]

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But where the varied traits sought to be com-
bined in a Shasta daisy are in question; or the
many qualities of a commercial cherry or prune,
the case assumes new complexities.

Hence it is that my records tell of tests applied
to about half a million seedlings of the daisy;
seven and one-half million seedlings of various
plums, and the like.

Hence also the constant necessity of what my
neighbors speak of as ten-thousand-dollar bonfires
in my orchard, when we burn seedlings that have
been inspected and found wanting. To burn
65,000 hybrid blackberries in one pile, as I once
did after saving perhaps half a dozen individual
vines, seems like willful extravagance to the
casual observer, but it is an unavoidable incident
in the search for perfect fruits.

Such prodigal use of material implies a large
measure of experience in the handling of seeds
and the growing of seedlings. In point of fact,
it might be said that this is the most important
part of a plant-breeder's task, so far as the
practicalities of experiment are concerned. It is
part and parcel of his daily routine.

It is highly desirable, then, that the would-be
experimenter should gain a clear understanding
of the essentials of method of caring for seeds and
cultivating seedlings. So it is my purpose in the

[114]

"Flat" With Layer of Gravel

A layer of gravel is put at the bottom oj the germin-
ating box to facilitate drainage and aeration, both oj which
are very essential to the proper growth of the plant roots. Mr. Burbank
regards this detail as very important.

LUTHER BURBANK

succeeding pages of this chapter to give a few
practical hints as to various aspects of the subject.
Thus summarized, the lessons I have learned in
the hard school of experience may enable the
reader to avoid some pitfalls and to make certain
experimental shortcuts.

KEEPING SEEDS OVER WINTER

To begin at the beginning, let us note that the
preservation of .seeds over winter calls for careful
attention.

All fruit seeds except those of apricots and
almonds, when removed from the fruit, are at
once placed in slightly moist, coarse sand or fine
gravel or in sterilized sawdust

In warm climates the boxes containing the
seeds are then buried on the shady side of a
building or tree where they will become neither
too dry nor too wet. The object is to keep the
kernels as nearly as possible in their original
condition.

If tree seeds, especially those of the cherry,
the pear, and the plum once became thoroughly
dry, it is difficult, and in some cases impossible,
to induce them to germinate. An important
function of the pulp of these fruits, in the original
wild state, was, presumably, to keep the seeds
moist until the season for germ motion.

I have elsewhere called attention to the

[116]

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exceptional difficulty of keeping stoneless plums
and prune seeds in condition for growing. Not
having the natural protection of the shell, they
tend to germinate too early, and of course they
are peculiarly subject to the attacks of insects
and of fungous diseases. Such seeds may best
be placed in cold storage as soon as collected and
cleaned, and kept at freezing temperature. Seeds
thus cared for will sometimes germinate almost
as quickly and readily as beans or corn. They
must not be planted too early in the spring, lest
their too prompt germination subject them to
injury from late frost.

Incidentally, I may note that grafts sent to me
from a cold climate have often been observed to
start with greater promptness, and grow better
than those from our own immediate vicinity
where the winters are mild. Cold seems to rest
the tissues and prepare them for rapid growth,
just as treatment with narcotic drugs has been
observed to do in certain interesting experiments
that will elsewhere be referred to more at length.
OUT OF DOOR PLANTING

In California, plum seeds are usually planted in
January or February, in a little furrow about an
inch deep. A furrow may be made accurately
and expeditiously with the aid of a triangular bit
of board an inch or so wide nailed across another

[118]

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longer piece, so that when drawn along a garden
line it makes a narrow furrow of exact width and
uniform depth throughout.

Plant the seeds about one-half inch to an inch
apart, and cover with a thin layer of soil; then
fill the furrow with sawdust. This is an important
matter with cherry and plum seeds, especially
with the stoneless ones which must be given every
inducement to push through the soil. A heavy,
compact soil placed over cherry and plum pits
prevents a large number from pushing up to the
light. For this reason a sawdust covering is
preferred, and it also regulates the moisture
with exactness, allows for sufficient aeration, and
equalizes the temperature. Moreover, the saw-
dust is distasteful to slugs, thrips, cut-worms, and
other insect pests.

Peach, nectarine, and apricot seeds are planted
farther apart and a little deeper; quince, pear and
apple seeds are planted about the same as plum
seeds, both as to distance and depth, or in large
lots may be rather thickly sown in drills or
furrows six or eight inches wide and eighteen to
thirty inches apart.

For growing seedlings of conifers — pines and
their allies — cold frames or shallow boxes are
used filled with mellow sandy loam; or the seed
may be sown broadcast or in rows in cold frames

[120]

"Flats" With Sprouting Seedlings

All manner of seeds are sown in the "fiats" and
Mr. Burbank has so perfected the method that he usually
sprouts ninety-nine seeds in a hundred. The same method is used
for the commonest flower and the rarest exotic. "Flats" grow-
ing hybrid cactuses are side by side in his green-
house with those containing orchard fruits,
and flowers of many species.

LUTHER BURBANK

without boxes. The object of the cold frames is
to shelter from hot sun and drying winds and in
cold climates to prevent freezing.

If the season is short or if warm weather
comes on suddenly, it is sometimes desirable to
soak seeds in water before planting.

After being in the water several hours they
should be drained and set in a warm place
where germination can start quickly. In this way
growth may sometimes be advanced by a week
or more. But such forced germination is not
usually necessary or desirable. If carried too far
before planting, it endangers the growth. On the
other hand, the very early plants often escape
cut-worms and other insects by attaining a fair
growth before these pests put in an appearance.
BOXES FOR SEEDLINGS

Valuable plants to be grown in large quantities
from rare seeds, may best be started in small boxes
or "flats" indoors, under glass or in sheds made of
laths or slats so spaced as to allow free entrance
to air and sunshine.

Boxes of the right design and construction are
far better for this purpose than pots or earthen
pans. The boxes or "flats" that I have used for
twenty years are made of redwood lumber.
Where this cannot be obtained, cypress is nearly
as good, but soft pine is not durable and should

[122]

The

Seedlings in the Greenhouse

'Flats" are here shown at a later stage, when

them

c * i.uto uic uc re snuwn at a later stage, wnen
some of the seedlings have been transplanted to give t
room, and have attained considerable proportions. Much time is
saved by thus developing the seedlings in the
greenhouse over winter.

LUTHER BURBANK

be avoided. Eighteen inches square, outside
measure, four and one-half inches deep, inside
measure, is a good size.

Two opposite sides are of common board
lumber three-quarters or seven-eighths of an inch
thick; the other sides, are a little less than half
an inch thick. The bottoms are made of redwood
"shakes" which are about one-fourth of an inch
thick; two or more spaces of an eighth of an
inch being left for drainage. Across the bottoms
are nailed three strips which add rigidity and
strength as well as affording better ventilation
and drainage. After all the parts are carefully
fitted, the joints are sometimes dipped in linseed
oil, before being strongly nailed together. This
gives durability and tends to prevent the nails
from rusting out.

These redwood boxes may be used for many
years if sterilized once a year by being placed for
about three or four minutes in boiling water.

A suitable soil is the first requisite in raising
seedlings in boxes. The mixture which I have
generally found best for use in the early winter
for raising seedlings in boxes in the greenhouse,
is compounded about as follows : One-half clean,
rather coarse, sharp sand; with about forty per
cent, of some good pasture or forest soil which
generally contains more or less leaf mould. To

[124]

3 *

LUTHER BURBANK

this is often added ten per cent, finely powdered
moss or peat. These mixtures, with the addition
of about one or two per cent, of fine ground bone
meal or superphosphate, make soils in which
seeds of almost any kind of plants from any part
of the earth will germinate. Seedlings thrive in
this soil until they are ready for transplanting.

If seeds of choice plants are to be grown, the
soil is sterilized by a thorough scalding to destroy
any fungus or insect pests.

Usually we find it suits the plants better if a
part of the soil last prepared is left over for use
with the new mixture, like yeast for a loaf of
bread, and I always prefer to have a little of the
old on hand for this purpose.

Common sharp sand, if the right texture can
be obtained, is far better for cuttings than the soil
just described. The sand found along creek or
river banks is generally free from injurious insects
or fungous diseases. But for rare cuttings and very
choice seeds, this should be rinsed by pouring
large quantities of water through it, at the same
time stirring or jarring the material.

In filling the boxes, coarse gravel, such as will
just pass through a half -inch mesh, or a little
smaller, is placed one-quarter to one-half inch
deep over the bottom of the box. This ensures
perfect drainage and sufficient aeration, both of

[126]

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which are of the utmost importance. The box is
then filled, to within about an inch of the top,
with the sand or special soil. Make the filling a
little shallower for fall planting, when we expect
much cool, damp weather, and slow growth, to
prevent drowning or "damping off" of the seed-
lings during the winter; a little deeper for spring
planting, to prevent too sudden drying out, and
otherwise to regulate the amount of moisture.

This may seem like a matter of small conse-
quence, but such details often determine success
or failure.

THE SEEDLING KINDERGARTEN

All ordinary seeds are sown quite thickly in
the boxes and covered lightly with the same soil,
according to the size of the seed — just a dusting
of soil for the finest of seeds, and an eighth to a
quarter of an inch for the larger ones.

In testing new varieties, ten or twenty different
kinds of seeds may be planted in sections in one
box, each marked with a small wooden label,
tacked on the upper edge of the box with the
name, or the reference-book number, of the seeds.
After the seeds are planted, the surface is pressed
down with a flat piece of board until it is level,
smooth, and solid.

Instead of watering the surface by any sprink-
ling process from above, the boxes are placed,

[128]

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LUTHER BURBANK

after the seeds are planted, into a square pan
containing water sufficient in depth to rise nearly
or quite even with the surface of the soil. In a
few minutes the water saturates the soil and entire
contents of the box, without disturbing the seed,
and without packing the soil in the least. The
boxes are then removed and tilted to one side so
that the superfluous water can slowly drain out.

A thin layer of moss sifted over and under the
seeds acts as a non-conducting blanket, equalizing
the temperature and retaining moisture.

A layer of gravel above the moss protects the
seeds or young plants from being washed about
when they are watered from above, as they are
usually sprinkled after a few weeks of growth.
The thin covering of gravel also wards off fungous
diseases which afflict tender seedlings. All this
may seem like unnecessary trouble, but it is
absolutely necessary if one wishes to attain the
best success. No part of the program caii be
omitted without risk of loss or injury to the seeds.

When the seedlings have two to four leaves it
is best to transplant them into another box,
whether they are large or small, in order to give
them more room in which to develop.

In each box used for raising fruit seedlings
we put about sixty-four, or sometimes late in the
season as many as one hundred specimens. They

[130]

Setting Out Plants From the "Flat"

When the seedlings are sufficiently hardened, if the

weather is suitable, they are transplanted into the open garden.

The "flats" are taken into the garden, so that the transfer may be made

directly and with the least possible damage to the roots of the

plant. An ordinary trowel is the best implement

for transplanting most seedlings.

LUTHER BURBANK

are allowed to grow until toward spring when the
weather becomes warm, about the time of the
blooming of fruit trees, when they are ready to
be transplanted to the open fields.

Some of the smallest plants raised in green-
houses, like calceolarias, lobelias, begonias, ferns,
etc., may readily be transplanted, even when they
can hardly be seen, by lifting them on the end of
a moistened quill, pencil, or small knife blade,
placing them on the soil which has been previously
moistened as before described, then covering with
a glass for a few days until the young plantlets
can get established.

This is the quickest and best method of trans-
planting some of the smallest seedlings, and
though apparently tedious is often the most
speedy and profitable mode.

GOING Up A GRADE

In transplanting all small seedlings, they are
placed in straight rows in the boxes; usually eight
rows with eight plants in a row in the eighteen-
inch boxes; but, for larger individuals, six rows
of six plants; or, on the other hand, ten rows of
ten or even twelve rows of twelve in case of the
smallest ones.

After standing in the greenhouse for a week
or two, the boxes of seedlings are removed,
usually to a sheltered place out-of-doors, in order

[132]

Making a Trench /or Cuttings

Where cuttings are to be planted, a deep trench may
best be made by inserting a flat spade and moving the handle
back and forth a few times. The same method may be used JOT trans-
planting seedlings that have long roofs, it being particu-
larly desirable that the roots shall not be
disturbed, lest growth be
retarded.

LUTHER BURBANK

that they may continue growth and become har-
dened through exposure to sunshine and outdoor
air. Later, they may be safely transplanted into
other boxes, giving them more room for growth,
or to the field where they may be planted in long
rows about four feet apart, so that they may
afterwards be cultivated by horsepower in the
usual way.

In general the treatment here described is
employed for cactus, berries, lilies, begonias,
grasses, potatoes, roses, ferns, or any of the
thousands of species of domestic, foreign, arctic,
or tropic seeds which are received from collectors.

In transplanting, it is best to have the boxes
of plants carried into the field, and with most
plants it is best to saturate the soil in the boxes,
letting them drain a little before attempting to
transplant. Then with a trowel they may be taken
up with the dirt surrounding the roots and set out.

After marking the rows with a garden line, a
long narrow crevice is cut by inserting a flat spade
and moving the handle back and forth a few
inches. The plants can be rapidly placed in the
crevice thus made. One side of the soil is pressed
down with the foot or with a tamper, and packed
quite firmly against the roots.

Then more soil is drawn in with a hoe or rake
and carefully placed about each plant, after which

[134]

Setting Out Cuttings in the Trench

This picture shows Mr. Burbank's method of setting

out cuttings in the trench prepared in the way shown on page

135. The soil on one side of the trench should be pressed against the

cutting, and firmly packed with the hand, no other

implement being required at

this stage.

LUTHER BURBANK

a common garden rake is used in leveling and
loosening up the soil along each side of the row,
which prevents "baking" and helps to keep the
temperature equable and the soil moist. The
most tender plants treated in this way are saved
almost without exception.

OUT IN THE OPEN

Nearly all plants should be set out in the field
somewhat deeper than they grow in the boxes.
When plants have long roots these should be
straightened out and placed as deeply as possible
in the soil to give them a good start by the time
the dry summer weather commences. Otherwise
the young plants could not, in some cases, extend
their roots fast enough to keep up with the
gradually disappearing moisture, and so might
die of thirst.

When seedlings are removed from the pro-
tection of the glass house to the open air, or in
transplanting in the fields, it is best, if possible,
to choose a time when there are no severe
winds, and when the sun is not too hot and the
atmosphere neither too dry nor too chilly.

Generally in California tender plants best
withstand moving from the greenhouse to the
open air just before or during a warm rain. At
such times the atmosphere is similar to that in
the greenhouse. Even under the most favorable

[136]

Tamping the Dirt Around the Cuttings

The setting out of cuttings is completed by tamping
the dirt rather firmly about them, either with the foot or with
a tamper like the one here shown. It is well to stir the surface subse-
quently with, an ordinary rake to loosen the soil at the surface,
so that it will not "bake." The picture shows also a
typical wooden marker, which in this case
records that the cuttings are the
roots of Standard stone-
less plums.

LUTHER BURBANK

circumstances they must be shielded from winds
or bright sunlight to which they are not adapted.

To accustom the tender seedlings to out-door
conditions, the flats are placed in square frames
about six feet wide and a foot or two high. These
are covered with a portable covering made of
common laths nailed on narrow strips of board,
so placed that the space between the laths is about
equal to the width of a single lath.

When the boxes of plants are placed in these
frames, it is best to have some slats underneath
so they will not rest on the ground; otherwise
fungous diseases are often communicated from
the earth to the soil in the boxes and to the tender
plants.

When the slat covering is kept over the frames
for five to twenty days according to the season,
the little plants will have adjusted themselves to
their new environment so that the slats can be
removed.

After a few more days of growth they will
probably be strong enough to be removed to the
open ground.

RUNNING THE GAUNTLET

Many tiny seeds, just as they are germinating,
may be destroyed in a short time by a cold dry
wind, or they may be killed even more quickly
by too much moisture and too little air.

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LUTHER BURBANK

Young seedlings may be killed by a common
fungus which causes "damping off." This is very
destructive where plants are grown too thickly
in the seed boxes especially in a close atmosphere
before transplanting. Sometimes a whole box
containing thousands of valued seedlings will be
destroyed in this way in a few hours, the trouble
generally commencing in little spots or patches
from which it rapidly spreads in all directions.

The tiny plants may most often be saved after
the fungus starts by applying a dusting of sulphur
or of coarse, dry sand or gravel. Sometimes if
placed in a cool, dry atmosphere so that the excess
of moisture is evaporated they may be saved.

The gravel, mentioned as sprinkled over the
moss when the seeds are planted, is the first and
best preventive of damping off. It covers the
soil with a substance on which the fungus cannot
readily establish itself, and thus separates the
unhealthy from the healthy plants. If good care
in general is supplemented by the use of this dry
sand or gravel, the fungus has little chance to
spread from plant to plant.

Of course, one is obliged to be on the lookout
for insect pests, slugs, cut-worms, crickets, aphides,
and thrip, which are sometimes very destructive.
Slugs, cut-worms, and crickets require instant
attention when they first attack the young plants.

[140]

QUANTITY PRODUCTION

The appetites of these pests often increase to
greater proportions than can be appeased by the
growth of the remaining plants and they must be
carefully sought in or under the boxes.

Sometimes slugs may be headed off for a time
by sprinkling lime, red pepper, quassia, or tobacco
dust in their paths. Thrip and the aphides are
best destroyed by fumigating the houses once a
week or twice a month with tobacco smoke; the
frequency may be regulated according to the
abundance and the persistence of the enemy.

All in all, it is a severe gauntlet that the
little seedling is called upon to pass. Yet if the
methods described in this chapter are carefully
followed out, it is possible to grow successfully
any seed, from whatever climate or soil or loca-
tion, that has the least germ of life within it.

These methods have been successfully used
with the seeds I am constantly receiving from
numerous collectors in Siberia, Brazil, Chili,
Argentina, Patagonia, Mexico, Central America,
the Philippine Islands, Alaska, British Columbia,
North and South Africa, Europe, India, South
Sea Islands, Australia, New Zealand, Central and
Western China, Japan, and Korea.

By sedulous attention to the details above out-
lined, the raising of seedlings becomes so certain
a procedure that the loss should not exceed one

[141]

Protecting Test Corn From the Breezes

To prevent a plant with a tall slender stalk Jrom

swaying about too much, a string may be tied about the stalk

in the way here shown. This hybrid corn is oj a gigantic variety

developed by Mr. Burbank, and it grows so rapidly that

there is particular danger oj injury

Jrom the wind.

QUANTITY PRODUCTION

plant in a hundred. And this, obviously, is a most
important consideration, especially with rare
foreign seeds or seeds produced by hybridizing
experiments that have involved exceptional care
and labor. To such priceless stock, any amount
of time and labor may be given ungrudgingly.
And even in planting common nursery stock one
soon learns that a thorough knowledge of the
requirements of the plants is essential to success,
and that cheap, careless work is always the most
expensive in the end.

A perusal of the foregoing pages will perhaps
serve, better than almost any other exposition,
short of inspection of the work itself, to give the
reader an inkling of the enormous amount of
mere mechanical labor — in addition to ceaseless
watching and patient waiting — required to bring
the seedling plant through the time of its tender
infancy. When it is further reflected that seed-
lings must be handled by thousands; and that this
care is, after all, only one of many essential stages
of each individual series of experiments in
plant development, perhaps a fairly clear notion
will be gained of the laborious — even though
fascinating— character of the task that confronts
the person who would develop a new fruit, a
flower of modified color, or a plant of altered
structure.

[143]

GRAFTING AND BUDDING

SHORTCUTS TO QUICK TESTS

NOWADAYS we hear of some remarkable
experiments in the grafting of animal
tissues, which strongly appeal to those
who have long experimented in the grafting of
vegetable tissues.

The experiments made by Dr. Alexis Carrel,
of the Rockefeller Institute in New York, are of
particular interest. It appears that Dr. Carrel
has devised a new method of suturing arteries.
With such a process, the plant experimenter of
course has no concern, for the juices of plants
are not transmitted in any such definite channels
as the arteries and veins of animals. But in
dealing with animal life the arteries are all
essential, and the process devised by Dr. Carrel
enabled him to perform grafting experiments such
as no physiologist or surgeon had heretofore found
feasible.

[VOLUME III — CHAPTER V]

LUTHER BURBANK

Not only did Dr. Carrel transfer sections of
arteries from one cat or dog to another animal
of the same species; but he also transplanted
successfully even such vital organs as the kidneys.

Moreover, what is more spectacular even if not
more important, he actually succeeded in ampu-
tating the leg of one dog and grafting it on the
amputated stump of the leg of another.

The transplanted limb presently made union
with its new stock, as a horticulturist would term
it, and the borrowed member became a permanent
portion of a new body, just as the cions of my
apple trees or plums become component parts of
the tree on which they are grafted.

All this, as I said, was so fully in keeping with
the familiar experience of the plant experimenter
that it had no peculiar interest for me. Perhaps
it seemed to me less wonderful than it really is
because my conception of the fundamental unity
of plant and animal life makes it appear to me
inherently plausible that such transplantation of
members should take place under proper surgical
conditions.

The only difference is that the method of
grafting plant tissues one upon another has long
been familiar, whereas no one knew just how
such grafting could be accomplished in the case
of the animal until Dr. Carrel found the way.

[146]

GRAFTING AND BUDDING

But I think what interested me most about Dr.
Carrel's experiments was the demonstration his
tests made of the limits of successful grafting
where the organs or members involved belonged
to different species. For, whereas he found that
the kidneys and spleen might be transplanted
from dog to dog, or from cat to cat, it was quite
out of the question to hope for a successful issue
if he transferred one of these organs from cat to
dog or from dog to cat. Even when the trans-
planted tissue consisted merely of a piece of
artery, it was found that the graft did not take
kindly to its new surroundings, unless the animal
were of the same species as that from which the
artery was taken.

Something inherent in the chemical compo-
sition of the tissues themselves makes every fiber
of the tissue of a cat, seemingly, more or less
antagonistic to the tissues of the dog.

We have already seen how the experiments
of Dr. Nuttall, of Cambridge University, demon-
strated that the quality of felineness or canineness,
so to speak, penetrates to the last drop of the
blood; so it is not surprising to find from this
independent source that the same characteristic
differences extend to the solid tissues.

And of course I am at once reminded of the
similarity of experiences of the grafter of plants.

[147]

LUTHER BURBANK

Here also there are sharp limits fixed to the
feasibility of the grafting method. You may
transfer the twig of an apple to the corresponding
limb of another apple tree, however widely dif-
ferent, with entire facility. You may similarly,
although with far less facility, make a graft
between twigs of the apple and the pear. In the
same way you may combine branches of the
different members of the family of stone fruits-
plum with apricot, peach with almonds, and the
like. But if you attempt to ignore the larger
barriers, and strive to graft seed fruit upon stone
fruit — apple or pear on plum or peach — your
effort will result in failure, just as Dr. Carrel's
experiments resulted in failure when he attempted
to transpose the organs of cat and dog.

It would be interesting if Dr. Carrel were to
extend his experiments so as to test the possi-
bilities of transposing the organs of different
species within a family — say from wolf or fox to
the dog, or from lynx or leopard to the cat. Here,
to judge from our experiments with plants, the
probability of success would be far greater.

At all events, we are commonly able to make
such grafts as we choose between different species
of the same plant genus; and we may reasonably
infer that the same thing might be possible in the
case of animals.

[148]

^ o

o a

3 3
R.A-2

LUTHER BURBANK

It has also been found that in plant life where
there has been much crossing either naturally or
by intent in the past that most striking individual
differences appear. Some individual seedlings
among any lot of such crossbred plants (all of
which may have come from the seeds of a single
variety), will thrive when grafted on certain other
species or varieties even better than on their
own roots, while other individual varieties refuse
to combine or grow under any conditions; for
instances, the common French prune thrives better
on almond roots than on its own, the golden drop
plum will not live when grafted on the peach
while some of its nearest relatives, the common
French prune and others, grow, thrive and produce
fruit abundantly. It thus appears that artificially
produced varieties may acquire really specific
difference of a profound nature.

THE MUTUAL INFLUENCE OF CION AND STOCK

Leaving the solution of this problem to the
physiologist, however, let us turn to the specific
task in hand, and consider that very important
part of the plant experimenter's task that has to
do with the grafting of vegetable tissues.

It is convenient to recall that the trunk or
branch upon which a twig is grafted is called the
stock, and that the transplanted twig itself is
spoken of as the cion. The practical methods of

[150]

Cutting Stock /or Whip Grajt

The stock cut on one side is split with the knife to
receive a don cut as shown on page 149. The picture shows
the exact method of procedure. It will be seen that this is a modifica-
tion of the cleft graft depicted in the frontispiece and on
later pages of the present volume. The whip
graft is used for small branches^
usually not larger than the
one here shown.

LUTHER BURBANK

grafting, as applied to different varieties of plants,
will be detailed in a moment. But first I wish to
consider very briefly the mutual influence that
cion and stock exert upon each other.

That there is an intimate chemical and vital
relation between the immediate living surfaces of
stock and cion admits of no question. The very
fact that we cannot cause plant tissues to make
union unless they are of allied species, is in itself
sufficient proof of this. Moreover, the fact that
the cion must receive its entire supply of water,
conveying all nourishment except carbon (which
is drawn from the air) through the medium of
the tissues of the stock, suggests that there must
be a uniformity of chemical composition between
the two that might be supposed to amount almost
to identity; particularly after the cion has been
in place for a term of years, and has grown from
a tiny twig to a large limb.

Yet, in point of fact, there is abundant evidence
that the cion maintains its original identity of
character from first to last. This may be more
readily understood when we know that all plant
food is developed within the foliage. To be
sure the roots supply water, the universal
solvent and transportation agent of all life, and
small quantities of certain minerals and organic
substances in solution, but these are not digested

[152]

Whip Graft in Place

The cion and stock shown on pages 749 and 151

respectively are here placed together in such a way that the

cambium layers oj the bark of the cion and stock come in contact. Only

this inner layer of the bark is composed oj active living cells, and '

the graft will be a failure if the living tissues of stock and

cion are not in contact. It will be seen that only

one edge of the cut surface of the cion is in

contact with the cambium layer

of the stock. But this serves

every purpose.

LUTHER BURBANK

for assimilation as plant food until combined with
carbon dioxide which is transformed in the leaf
cells under the influence of the active rays of light,
first into fruit sugars and by later transformation
to cane sugar but oftener to starch, a more stable
form of food substance, in which form it is
most commonly stored in seeds, bulbs, tubers or
enlarged roots or stems, or to wood and less often
to various other substances used in the economy
of plant life and quite often useful to animal
life and to the industrial life of man. These
transformations are presented to us in the various
food products and the numerous gums, rubber,
coloring materials, drugs, oils, and perfumes.

Thus it will be seen that every organic structure
on the earth, every plant and animal whether of
earth, sea or air, including man himself, is wholly
dependent upon the food always first developed
in the leaves of the plants.

But to return to our cions — a twig of the Bald-
win apple, grafted on a wild crab apple tree, will
produce Baldwin apples, and not wild crab apples.
Moreover, the Baldwin apples thus grown will be
identical in appearance and flavor with those that
grow on the tree from which the cion was cut.
This seems very mysterious, but the like of it is
matter of every day observation in the orchard of
the up-to-date fruit-grower.

[154]

Whip Graft Waxed

AJter the don has been accurately placed, as shown

on page 153, the exposed surfaces, including the entire body

of the cion, are painted thickly with grafting wax, applied warm with a

brush. If the wax is rather hot, it should be applied first about

the bark of the stock, and then carried over the cut surface

as it cools. The method of applying the wax with a

brush, instead of with the fingers as was

formerly done, is a great time saver.

LUTHER BURBANK

Nevertheless, the question has more than once
arisen as to whether cion and stock may not exert
upon each other an influence of a profoundly
modifying character.

That such may be the case, to the extent
of producing a poisonous influence, has been
observed in the case of grafts between species
somewhat distantly related. It has been observed,
for example, that some of the English plums unite
with the peach, and do fairly well for a time,
while others refuse to unite under any circum-
stances, and still others when budded or grafted
on a peach stock seem to poison the peach tree,
even causing its death. Yet, on the other hand,
the French prune will often grow better on the
roots of the almond or the peach than on its own
roots.

In each of these cases, it would seem, there
must be an influence, in one case harmful, in the
other beneficial, transmitted between cion and
stock.

It will be observed that such influences as these
merely extend to the life or vigor of the plant,
and have nothing to do with the question of
transferring its inherent characteristics. And it
is universally admitted, that, as a rule, the influ-
ence of stock on cion, or of cion on stock, is
thus limited. A cion of tender race may thrive

[156]

Whip Grajt Bandaged

The process of grafting illustrated on preceding pages

is completed by wrapping the waxed surface with a bandage,

to give further protection, and hold the don more firmly in place until

union is effected. It will be seen that stock and cion are cut in

such a way that they interlock rather firmly, but additional

stability is given by the bandage. It is obviously

desirable that the cion should not move

while the tissues are uniting.

LUTHER BURBANK

on the roots of a hardy stock, for the simple
reason that these roots have vigorous growth and
large capacity for imbibition of nourishment.

But just as you cannot make a dog and cat
identical in constitution merely by feeding them
the same food, so you cannot cause a grafted cion
on your peach or pear or apple tree to conform in
shape or constitution to the stock on which it
grows merely by giving it the same nourishment
that the stock receives— for as explained above all
the most important functions of plant life are
carried on in the leaves. Thus we may have an
explanation of the fact that the graft governs
the root almost absolutely as to variety or
individuality, while the roots are purveyors for
the foliage.

SAP-HYBRIDISM

Nevertheless, I have had at least one experi-
ence in the course of years of practice in grafting
that seems to demonstrate the possibility of the
transfer from cion to stock of qualities that
transform in a very tangible degree the essential
characteristics of the plant.

I refer to a case in which the twig of a purple-
leaved plum that I received from France was
grafted on an old Kelsey plum tree which stood
just at the corner of the vine-covered cottage on
my old place in Santa Rosa.

[158]

GRAFTING AND BUDDING

The graft was made in the season of 1893. I
was exceedingly anxious to hybridize this new
and interesting importation with some of my
plums, so I watched it carefully. But much to my
disappointment, no blossom or signs of blossom
appeared during the year. So there was no
possibility of making such a hybridizing experi-
ment as I desired.

Imagine then my astonishment when from a
quantity of seeds gathered from the Kelsey tree,
there grew next season, among other seedlings,
one with deep purple leaves. This strange seed-
ling proved to be a thoroughly well-balanced cross
between the original purple-leaved graft that I
had imported and the Kelsey upon which the graft
was growing.

There was a most perfect balance in foliage,
fruit, and growth so far as I could judge. The
tree was light purple in foliage throughout the
season. Its fruit was small, nearly globular, and
purple in color even when only half grown.

Everything about the appearance of this
strange seedling seemed to suggest that it was
a cross between the purple-leaved plum I had
imported and the Kelsey. There was no other
purple-leaved plum within thousands of miles.
My cion had not bloomed, and so crossing could
not have occurred in the ordinary way.

[159]

LUTHER BURBANK

So I can see no escape from the conclusion
that this was a case of so-called sap-hybridism,
the very existence of which has been doubted.

The purple-leaved cion had seemingly influ-
enced its host in such a way as to produce what
was to all intents and purposes a hybrid progeny.

The new purple-leaved seedling was grafted
upon an old tree, and in due course I produced
several thousand second and third generation
offspring from the original seedling. The fruit is
of a characteristic red color, and in flavor it
closely resembles the fruit that the original purple-
leaved cion subsequently bore. In size the fruit
is intermediate between that of the purple-leaved
cion and that of the Kelsey.

The descendants of this hybrid stock vary in
the second and succeeding generations, just as they
might be expected to do had they grown from
a hybrid seed produced by pollenation; thus
affording additional evidence that we have to do
with an actual case of sap-hybridism.

GRAFTING TO SAVE SPAC^E AND TIME

I record this case thus at length because of its
extreme unusualness.

Never in the entire course of my wide
experience have I seen another case in which I
could trace such definite influence between the
grafted cion and its foster parent. And so we may

[160]

mi?
JPkl

LUTHER BURBANK

take it as a safe general rule that a cion, however
grafted, will retain the characteristics of its parent
stock, and that the tree on which it grows will
be fundamentally uninfluenced, so far as the
character of its fruit is concerned, by the intruder.

It is not at all with the expectation of
influencing the fruit product of either cion or
stock that the familiar process of grafting is
resorted to. The chief object of grafting, as
practiced in my orchard, is to economize space
and save time. As to the former point, it will
be obvious that where scores or hundreds of
twigs from different seedlings are grafted on
limbs of a single tree, we are enabled to watch
developments among these hundred of specimens,
and by uprooting the original seedlings to utilize
the ground they occupy for other purposes.

As to time saving, I have discovered that by
grafting small cions near the tip of the limbs of
the foster parent, instead of near its trunk, the
cion comes much earlier to maturity, and bears
fruit in the second season instead of waiting until
the third or fourth, as it otherwise would do.

So it is that on a single tree in my orchard
almost a thousand different seedlings may be
tested simultaneously; and by the practice of
selection of early-bearing varieties during the past
thirty years, I have produced seedlings of a type

[162]

1*31

QJj

LUTHER BURBANK

which almost invariably bear the second year
from my grafting. Indeed, so universal is this,
that not one unfruited cion in a thousand will be
saved for the third year unless it possesses some
remarkable quality of growth, or shows peculiarly
prominent and rounded buds, associated with the
broad foliage that betokens unusual possibilities
of future fruit-bearing.

The reader who has followed the accounts
of the long series of experiments necessary to
develop say an early-bearing cherry or a stoneless
plum will appreciate in some measure the value
of a system of grafting which shortens by two
or three years the interval between successive
generations.

It will be readily comprehensible that by the
use of these grafting methods I have been able
to attain success in development of new varieties
of fruits in half the term of years that would
otherwise have been required.

GENERAL PRINCIPLES OF GRAFTING

The single principle that underlies all success-
ful grafting, is that the layer of tissue called the
cambium layer, lying just beneath the bark of
the twig, shall be brought in intimate contact with
the corresponding layer of tissue of the stock on
which it is grafted. The life-giving sap flows
through this thin layer of tissue only. As to the

[164]

Cleft Graft Waxed and Unwaxed

At the left, a cion inserted in the cleft, constituting a

cleft graft. At the right, a cleft graft completed, all but the

bandaging, by the application of the grafting-wax. The manner of

cutting the cion for insertion in the cleft is shown on page

i8g. The cion is cut in wedge shape, one

edge of the wedge being thinner

than the other.

LUTHER BURBANK

central woody tissues — the so-called heart of the
twig — there will he no union between stock and
cion in any case.

But this is of no consequence since the new
growth of wood soon covers the trivial wound
with which the cambium layer will make ready
union under favorable circumstances; and the
growth will continue outward, year by year, until
ultimately the cion and stock are so firmly joined
that they constitute a branch scarcely less strong
than the ungrafted branches of the tree.

But unless the living tissues of the cambium
layer are accurately joined, no union can take
place, and the graft will be a failure.

If this essential principle is borne in mind,
the process of grafting becomes a comparatively
simple one, and one that may be carried out suc-
cessfully by amateurs with very little preliminary
practice.

A few specific hints as to the details of the
method may, however, be of service. So I shall
give a brief account of the methods employed in
my orchards, where the process of grafting is
carried out thousands of times each year.

Grafting may be divided under three headings :
(1) Grafting proper, in which a cion or small
shoot is inserted into or upon the stock; (2)
Inarching, in which the cion is left attached to

[166]

Side Graft in Position

The side graft is made by bending a branch and

making an oblique incision with a knife. The cion is cut in

wedge shape as for a cleft graft, and it is of course inserted in such a

way as to bring the cambium layers in contact. The process

is completed by waxing and bandaging as with

the other forms of grafting.

LUTHER BURBANK

its parent stock until union with the new stock
is completed; (3) Budding, which consists of the
insertion of a single bud upon the cambium layer
of the stock. There is no fundamental difference
between the three processes; they are merely
different methods of accomplishing the same
purpose.

Grafting may be more or less successfully
carried on at any time of the year. But during
the spring and early summer months the vital
cambium zone is usually at the maximum of
activity, forming wood tissue from its inner
surface, and bark from its outer surface. At this
time of maximum growth, wounds are rapidly
healed, and union between a cion and stock is
most rapidly secured. Nurserymen and fruit
growers take advantage of this fact.

The most satisfactory results almost always
follow spring grafting or summer budding. It is
necessary, however, that there should be activity
enough in the sap movement to form the cellular
connection between the stock and the bud before
the latter perishes from drying out; sap flow is
also necessary to allow the bark to be lifted
readily from the cambium for the insertion of
buds.

The best success usually follows the grafting
of mature, or nearly mature, buds in the case

[168]

Side Graft on a Root

This does not differ from the ordinary side graft

except that the don is inserted in an incision made on the root,

which is exposed by digging away the earth. The side graft has the

advantage of not splitting the stock, and if the incision is

made of just the right size, it may be possible to

bring the cambium layers of the bark in

contact on both edges of the cion.

LUTHER BURBANK

of trees and shrubs; though young tender buds
often thrive nearly as well.

THE MORE COMMON METHODS

The best and quickest way to graft young
seedlings is by "side" grafting. This graft is made
by taking a piece of the new wood from the tree
to be multiplied, about 2% inches long with well
formed buds on it. Slice off both sides of the
lower end of the graft in the form of a sloping
wedge, the cut on each side being not much over
one inch long. Both sides should be alike, but
one of the edges should be thicker than the other.

The tree to be grafted is bent to one side with
the left hand. With the right hand a sloping gash
is made downward on one side of the tree just
above the ground, and the graft, described above,
is pushed down into this cut as far as it will go.
The cambium layers of the cion and seedling
meet at some point, and a union of the tree is
formed. After the cion has been placed, the tree
is allowed to spring back to its upright position,
and is at once cut off with a pair of pruning
shears, about two inches above the graft.

Warm wax is often applied with a small paint
brush over the wound to keep out the water,
germs, and dry air, though waxing is often omitted
with good success if the graft is well covered with
earth leaving a single bud above the surface.

[170]

The Root Graft Completed

. In side grafting to the root, as shown on page 160
it is not necessary to use wax, as the dirt will afford sufficient
protean when replaced and tamped about the don. It may b? desir-
able, however, to cover the exposed end of the
cion with wax.

LUTHER BURBANK

In grafting cions on the branches of trees, as in
transforming large trees or whole orchards, the
so-called "cleft" graft is usually employed.

In preparing for this, the branch of the stock
tree is sawed off at a convenient place, the exact
position being determined by the character of
the experiment. If we are seeking to make a
permanent tree, the graft is implanted upon the
limb not more than a foot or two from the trunk.
But where it is intended merely to test the cion as
to its fruiting possibilities, time being an object,
it is placed far out among the smaller branches
by what is called the "tongue," or "whip," graft.

In sawing limbs over an inch thick to serve
as stocks, care must be exercised that the limb
does not split. In order to avoid this, saw part
way through from the top, and finish it by sawing
from the bottom. Most persons who graft do not
trim the stock after it has been cut, but I have
found that the cambium layers join much more
readily if the top of the stock is trimmed carefully
with a knife so that it is smooth all around the
edges. Clean incisions heal best with vegetable
just as with animal tissues.

In making the "cleft" graft, the stock is split
with a grafting tool. The wedge shaped portion
of this tool is for the purpose of holding the cleft
open until the cions have been inserted. The

[172]

Crown or Bark Graft

For this graft the stock is sawed off as ij for a cleft

graft, but the incision is made, as shown above, to include

the bark only, exposing the cambium layer. The cion, cut wedge shape

is inserted, and a waxed bandage is applied. The cion here

is not at first held quite so securely as in case of

a clejt graft, but, on the other hand, the

stock is not split, which

is an advantage.

LUTHER BURBANK

cions are then cut and connected with the bark
usually one on each side of the cleft. When the
tool is removed, the sides of the stock hold the
cions tightly so that it is seldom necessary to tie
a string or piece of cloth around the graft. It is
usually best to put on a piece of cloth, however,
after waxing. This insures more uniform results.

Grafting wax, a formula for which will be
given presently, is usually applied several inches
below the crack which was made for the cleft
in which to insert the cions.

In some cases, however, the stock will later
crack below the point where the grafting wax was
applied, and when this occurs there is great
danger of the graft dying. For this reason it is
wise to visit the grafts several times at intervals
of a week or so and where any open crack is
found, additional wax should be applied.

There are various modifications of the cleft
graft. One is used for the walnut and fig which
it is almost impossible to graft by the common
cleft graft.

Modifications are made as follows: Instead
of splitting the cleft, triangular grooves are made
with a fine-toothed saw on several sides of the
stock. The edges of these splits are pared smooth
with a sharp knife and the cions which are
usually large, after being carefully fitted, are

[174]

Bridge Graft

This is allied to "inarching," in which the cion is

lejt upon its original root until union is made, the plant jrom

which the cion is to be taken being planted close to the one that is to

serve as the stock. The two are Drought together, and the bark

sliced Jrom a branch of each so that the cambium

layers come in contact. After union, the

stock is cut above and the cion

below, thus leaving the

cion on a new

stock.

LUTHER BURBANK

driven into these slits with a small mallet. Strong
cords are then bound around the stock to help
keep the grafts in place until they have united
with the stock, when they may be cut to give room
for further growth.

All cut surfaces should be carefully waxed as
in ordinary cleft grafting.

It is well to tie ordinary grocery sacks over the
grafts, covering the stock as far down as it has
been cut. These are allowed to remain until the
buds have made a good start when they may be
torn open and finally removed.

In making all grafts, care must be exercised in
getting the cuts on cions and stocks smooth, so
that the parts may fit closely together. In the
cutting of each side, a single bold clear cut is
better than whittling and trimming.

The "tongue" or "whip" graft is used in making
bench (i. e., indoor) grafts and sometimes in "top
grafting" trees. Top grafting consists in placing
grafts on the various branches of a tree in order
to change it over to the new variety. The tongue
graft differs from the cleft graft in that there is
a cleft and wedge on both cion and stock. These
interlock when closely pressed together as shown
in the accompanying picture. This mode of
grafting is seldom used except on limbs less than
one-half inch in diameter. It is very difficult to

[176]

Cutting Stock /or Top Grajt

A tree may be made over by cutting off its entire top,
and grafting cions to form a new head. Mr. Burbank recom-
mends that the cut edges be smoothly trimmed for this and for all other
grafts. The additional time and effort required to smooth
the cut surfaces with a knife will be amply repaid
by the better results attained.

LUTHER BURBANK

make the proper cut on limbs larger than this.
In top grafting large trees, it is often well to
graft only on the strongest limbs one season, and
on the smaller branches the next. In general
practice, however, a whole tree is usually grafted
over at the same time.

"BARK" GRAFTING AND "INARCHING"

In grafting chestnuts a modified method called
"bark" grafting is best. The cion is trimmed very
thin and quite a space is allowed for the cambium
layer to come into contact with the cambium layer
of the stock. A "T" shaped slit is made in the
bark of the stock, cutting through to the cambium
layer. The flaps about the vertical slit are turned
back, the cion inserted, and the lips of the bark
closed over it and bound firmly with a piece
of cloth or strong twine to give good support.
Grafting wax is applied freely.

Such grafts are usually made on a fairly large
stock where it would be impracticable to split
the stock. As a rule four cions are inserted on
one stock, for usually two of these die. If they
should all live, two should be cut out, as the grafts
do best when there are not more than two on one
stock.

"Inarching," as already stated, differs from
ordinary grafting in that the cion is left upon its
original roots until the union is made.

[178]

Top Grajts in Place

In this case a single relatively large cion has been

placed at the end oj each stock branch, so that the new head

will nave approximately the Jorm oj the original tree. Many orchard

fruits do better on foreign roots, and this method of top grafting

is a familiar ^ horticultural procedure. In Mr.

Burbank's orchards the grafted dons

are usually new varieties

to be tested.

LUTHER BURBANK

The plant from which the cion is to be taken
is planted close to the plant that is to serve as the
stock. The two are brought together and the
bark sliced from a branch of each so that the
cambium layers come together. This connection
is bound and waxed. After union has taken
place, the cion is cut off below the union and the
stock is cut off above it, thus leaving the cion on
a new stock.

This process is only exceptionally used, as it
requires too much time and expense, and with
most plants is usually no more successful than the
simpler methods of grafting.

GRAFTING WAX

Mention has been made of grafting wax, as
being very generally used to protect cion and
stock during the process of healing and union of
tissue. After testing many formulas, I selected
the following, and no other has been used in my
orchard for many years :

Eight pounds of common resin and one pound
of beeswax or paraffine (either will do if no acid
or alkali is present, though beeswax is generally
preferred) are mixed with one and a half pounds
of raw linseed oil. Boiled oils often contain
chemicals injurious to plant life. If the wax is
to be used in cold weather, it is better to use only
seven and a half pounds of resin and a half pound

[180]

Cutting the Bark to Receive a Bud

A T-shaped incision is made in the bark of the stock

on which the bud is to be grafted, and the edges about the

vertical slit are turned back, exposing the cambium layer. The slice

oj bark with the bud (see page 181) is then slid into this

pocket, and the bark of the stock is folded

about it and secured with

a string.

The Bud Graft Completed

This shows the completion oj the process oj bud-

grajting, preparation for which is shown on the opposite page

and on page 181. It is not necessary to use grafting wax, as the string

will hold the bark securely in position until union has taken

place. The string should then be removed, that

it may not constrict the tree.

LUTHER BURBANK

of beeswax in the mixture, thus giving slightly
thinner consistency.

The ingredients are slowly heated together
until the resin and wax are melted and all
thoroughly combined. This composition when
partly cooled is poured into pressed tin pans, to
make cakes of convenient size for handling. The
mixture sticks to the tin with great persistence;
but by turning the pan upside down and pouring
boiling water over it for a few seconds the wax
can be shaken from the pan.

These cakes are broken into pieces of con-
venient size, and in use the wax is kept warm
in any convenient dish or pan having a short
strong handle. The wax may be heated over a
small coal oil stove, and when applied to the
grafts should be much warmer than can be borne
by the hand, but not hot enough to scald the plant
tissues. If heated in a double heater, the outside
one containing water, the danger of overheating
is lessened.

If applied with care with a small paint brush,
first around the thick bark of the stock, and later,
as the wax on the brush cools, on and about the
cuts and open joints, no harm will result. The
plan of brushing the hot wax about the graft,
instead of applying it by the fingers in the tedious
old-fashioned way, saves nine-tenths of one's time,

[184]

Bud After a Year's Growth

The bud grafted as shown on page 183 may remain

dormant or take on immediate growth according to season.

It may develop a branch several feet in length in the course of a single

season. The stock should not be altogether cut away above the

bud at first, as in that case there may not be sufficient

circulation of the sap to stimulate growth. The

picture shows a branch grown from a

grafted bud, being trained to

upright growth.

LUTHER BURBANK

and does far better work than could ever be done
by the old method.

If the wax should prove to be too soft and
sticky, as is sometimes the case in very warm
weather, melt it over again with more resin
added. If too brittle, add a little more linseed
oil so as to bring it to the right consistency to
spread well, and at the same time "set" well on
cooling. It gives the most satisfactory results
when about the consistency of ordinary chewing
gum.

Properly applied, the wax serves as a valuable
protective and germ-excluding dressing, compar-
able in its function to the aseptic dressing applied
by the surgeon to wounds or after operations.
MULTIPLICATION BY BUDDING

There is one form of grafting which differs so
radically from other methods that it is often
thought of and spoken of as if it were a totally
different method. This is "budding"; that is to
say, the process of transplanting a single bud
from one tree to another. This is really only a
special case of grafting; it differs from other
methods only in that in ordinary grafting the
cion usually has several buds instead of a single
one. As a practical procedure, therefore, budding
has the advantage of supplying several grafts
from what by the other method would be only

[186]

Bud With Stock Cut Away

The process of bud-grafting illustrated in the pre-
ceding pictures is completed by the cutting away oj the stock,
so that the branch grown Jrom the ungrajted bud will assume upright
growth and make a new top on the tree. OJ course buds may
be grafted on branches of an old tree as well as on
the trunk oj a sap/ing, the process being
exactly the same in each case.

LUTHER BURBANK

a single cion. Therefore budding is generally
used for the production of nursery stock on
a large scale, or for the introduction of rare
varieties, grafting material for which is costly or
difficult to secure.

The method of budding is closely similar to
the method of "bark" grafting, already described,
except as to season — which, for budding, is June,
July, and August, while the trees are in full leaf.
A piece of bark about an inch and a half long,
with a well-ripened bud, is sliced from a twig of
the variety desired, the incision being just deep
enough to include the cambium layer and perhaps
a minute portion of wood.

The bark of the stock is slit horizontally and
vertically to form a T; the size of the slits being
determined by the size of the bud to be inserted.
The upper corners of the vertical slit are gently
lifted with a knife and turned back to reveal the
cambium layer. The bud is pushed under the
bark; the flaps of which are brought over it, and
securely tied. Waxing is not usually necessary.

In ten to fourteen days, the bud becomes
united to the seedling and the binding cord may
be loosened or removed.

The bud remains dormant, until the next
spring. When the leaves begin to start, the tops
of the seedlings are cut down to within two or

[188]

LUTHER BURBANK

three inches of the bud, all buds being at the same
time removed except the one inserted the season
before. Thus the vigor of the tree is thrown into
the new bud, and by fall we usually have well
branched trees from 3 to 6 feet high, according
to soil and climate, from the single bud which was
placed in the seedling the preceding summer.

Sometimes instead of allowing the buds to
remain dormant over winter they are placed on
the young seedling trees earlier in the season.
Fully ripened buds for such transplantation may
often be obtained in June or early in July. After
the bud is inserted, the tops of the young trees
are at once broken over at about half their height,
leaving only a piece of bark and a part of the
wood to continue circulation. If the whole top
is removed the result is failure.

When the weather is moist or where irrigation
is practiced, the buds will often start out even
before they are fully united with the stock, though
there is a great difference in this respect. Some
varieties of hybrid Japan plums and even the
common French prune often make 3 to 6 feet
of growth the same season.

These are called June buds by nurserymen.
When well grown they are excellent trees, as they
can be transplanted, leaving the whole root system
complete, whereas with trees two years old, some

[190]

GRAFTING AND BUDDING

of the roots have to be destroyed in transplanting.
Another great advantage in the June bud or
yearling over the larger two year old trees,
especially in California, is that the tops can be
cut down low to form heads of any uniform
height desired because all the side buds are young
and fresh.

HINTS AS TO HEADING AND CULTURE

With most fruit and ornamental trees, the
stocks are secured by planting seed. These are
planted during the winter in California, and
during the fall or early spring in the colder
Eastern states.

In general practice, seedlings of pears, cherries,
apples, etc., of one year's growth are purchased
by nurserymen. These are purchased from
persons who make a specialty of producing
seedling stocks in large quantities. A large
portion of these are imported from France, though
American seedlings are being more and more
used. These young seedlings are lined out in
rows for field culture about four feet apart, being
planted from six to twelve inches apart in the
rows.

During the summer following, usually in July
or August for cherries, plums, and peaches, and
in September for apples and pears, budding or
grafting may be done to best advantage.

[191]

LUTHER BURBANK

If there is a marked difference in rate of growth
of cion and stock, or if for any reason the two do
not blend to advantage, an ugly swelling often
results at the point of union; hence the experienced
grower avoids making such combinations. These
plant affinities cannot be foretold; they can be
determined only by experiment. As already
pointed out, the success, vitality, and growth of a
graft will very largely depend upon the affinity
between cion and stock.

Occasionally species from different genera may
be satisfactorily grafted.

For example, some of the pears often thrive
even better for a time and produce superior fruit
when transferred to a Hawthorn or apple stock.
Almond cions thrive well on peach or plum
seedlings. Apricot cions grow and thrive well
on seedling plum or peach stocks.

Cherry cions do well on seedling stocks of the
wild Mazzard cherry of Europe. The Mahaleb
cherry is sometimes used when it is desired to
have dwarf-growing trees. The peach generally
thrives on its own roots only. Apples thrive best
on their own roots or on various wild crab apple
roots.

Pear cions do well on seedlings of wild
or inferior varieties of pears. Most of the
seedlings grown in this country are grown from

[192]

Cions Showing One, Two, and Three Buds

A don with a single bud, like that in the center of

the picture, will serve the purpose, and may be employed

where wood is precious, as in case of a single seedling of a choice

variety. Ordinarily, however, a cion is cut to include two or

three buds, thus making allowance for the possible failure of

one or more buds. Small twigs like these, if grafted

near the ends of branches of an old tree will

bear fruit in perhaps half the time that

would be required if they were

left on their own roots.

LUTHER BURBANK

seeds secured from Europe. Quince stocks are
sometimes used for certain varieties of pears,
more especially for dwarfing and bringing into
early bearing.

Seedlings of the hardiest and most vigorous
growing varieties of plums, either European or
American, may be used for plum stocks. The
myrobalan plum from France is a favorite. The
peach is also used for some 'varieties. Stocks or
the seeds from which to grow them can usually
be secured from wholesale growers and dealers.

If it is desired to test the qualities of
hundreds or thousands of seedling fruits, a
knowledge of grafting is of the utmost importance,
as several hundred varieties may be readily
tested on a single tree.

On the Gold Ridge Farm there are single acres
on which ripen several thousand distinct varieties
of hybrid seedling plums that could not properly
be tested one each on a separate tree on less
than about seven hundred acres of land. Besides,
a seedling grafted into a bearing tree usually
produces fruit in two or three years, but if the
same seedling were planted as usual and allowed
to fruit, it might require five, ten, or fifteen years.

There is still another advantage in grafting
many seedlings in a single tree; a better
opportunity is afforded for comparative tests; if

[194]

GRAFTING AND BUDDING

scattered over a large orchard, some trees might
be in better condition, or have better roots or
better soil than others, and thus no accurate
comparative test could be made.

In grafting for the purpose of testing seedlings,
the weaker-growing seedlings are placed on
the strongest-growing branches of the tree, the
stronger growers being placed toward the outside
and lower down on the tree and on the smaller
branches.

When so many varieties are grafted on a single
tree, some may be extremely vigorous growers,
others only moderately so, and still others will be
weak, slow growers. In the winter pruning we
always take pains to give the weaker growers
plenty of space to develop, while the stronger
growers are severely pruned.

It is no small matter to prune properly a tree
on which several hundred varieties are being
tested. An ordinary pruner might ruin the tree
in a few minutes, by leaving the most worthless
varieties almost covering the tree, while smaller,
slower-growing varieties of great value might be
so crowded that they would either die or become
stunted and bear no fruit. This later aspect of the
process of grafting, then, is one that imperatively
demands the attention of the plant-developer him-
self, or of his most skilful assistants.

[195]

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LETTING THE BEES Do
THEIR WORK

NATURE WILL HELP Us
ALL SHE CAN

OUT in the desert regions of the southwestern
United States there grows a very remark-
able plant called the yucca, or Spanish
bayonet Doubtless you have noticed it from the
car window, or you may have seen it growing in
a garden. Its bristling array of bayonet-like leaves
gives it a very individual appearance, and the
cluster of creamy white flowers that it puts forth
on its tall central stalk gives it added distinction.

But even if you are familiar with the appear-
ance of the plant, you perhaps have never heard
the wonderful story of its alliance with a particular
species of insect, upon which alliance the lives of
both plant and insect absolutely depend.

The story is one of the most curious ones in
the entire range of plant and animal life. Gases
of so-called "symbiosis," in which an insect and a
plant are mutually modified for mutual aid, are

[VOLUME III — CHAPTER VI]

LUTHER BURBANK

common enough in nature. But so extreme a case
as that of the yucca and the insect that is its
inseparable associate is seldom duplicated.

The insect in question is a little yellowish
white moth, so unfamiliar that it probably has no
colloquial name, but known to the entomologist as
the Pronuba yuccasella. If you were to watch
closely you might see these moths visiting the
flowers of the yucca in the twilight. You would
require exceptional opportunities for observation,
if you were to discover precisely what takes place
during this visit. But entomologists have kept
watch to good purpose, and the terms of the
extraordinary coalition between the yucca and
the pronuba moth are now an open secret.

It appears that the female moth that visits the
yucca blossoms has developed a long ovipositor
with which she can pierce the tissues of the ovary
of the plant and so lay her eggs within it. Her
prime object in visiting the yucca flower is thus
to deposit her eggs. In due course the eggs hatch
and the growing seeds of the yucca will furnish
them a supply of food. So there is nothing very
remarkable about this part of the procedure.

The surprise comes when we learn of certain
maneuvers preliminary to the deposit of the eggs.
If you could watch the little moth on her visit to
the first flower, you would see her begin at once

[198]

LETTING THE BEES DO THEIR WORK

industriously to gather the adhesive pollen grains
with the aid of a curious pair of tentacles growing
about her mouth; tentacles unlike those of any
other moth.

As the pollen grains are gathered they are
rolled into a small pellet, and when this is of a
satisfactory size, the moth leaves the flower and
flies to another.

But here instead of continuing her task of
pollen-gathering, the insect makes her way to the
center of the flower and, piercing the basis of the
pistil with her ovipositor, lays her eggs among
the embryo seeds of the ovary. Then she crawls
carefully up the style and, poising at the tip,
pushes the little ball of pollen down into the
cavity of the stigma.

By this seemingly preconceived and carefully
perfected plan, then, the little moth has obviously
done precisely the thing necessary to insure
fertilization of the flower in which her eggs are
deposited, with pollen from another flower.

No plant experimenter, whatever his skill,
could have done the thing better.

Gross-fertilization is assured; the ovules among
which the eggs of the moth were deposited are
sure to develop, giving an abundant supply of
food for the larvae when in due course they are
hatched. The little grubs will grow and thrive,

[199]

LUTHER BURBANK

and presently will eat their way out of the
ovary and fall to the ground, where they will bury
themselves for a season; coming forth as adult
moths in the succeeding summer, just at the time
when the yucca is flowering.

SERVICE FOR SERVICE

At first glance it is not obvious how the yucca
profits by this curious arrangement.

But observation shows that the progeny of the
moth seldom or never consume all the yucca seeds
that are so conveniently stored about them. After
they have eaten their fill and have sought a new
shelter, enough yucca seeds remain to insure per-
petuation of the species. The progeny of the
moth have indeed taken toll of part of the crop
of yucca seeds in recompense for the services
performed by their mother.

But, on the other hand, had not the moth paid
its visit, the flower would by no chance have been
fertilized at all.

Here, then, is a case in which there is absolute
mutual dependence between a particular species
of insect and a particular species of plant. In the
desert regions it inhabits, the moth could find no
other place to deposit her eggs where food would
be assured her offspring; and in the burning desert
air, the stigma of the yucca, if not placed deep
within the tissues, could hardly endure exposure

[200]

LETTING THE BEES DO THEIR WORK

and still perform its function. The arrangement
between stamens and pistil of the yucca is such
that no other insect is likely to pollenize it, even
were there other insects at hand.

All in all, as I said, this is one of the most
curious and thought-provoking instances in all
nature of mutual dependence between an animate
creature and a plant.

One can scarcely leave the yucca and its strange
visitor without inquiring how so extraordinary
a coalition could have been brought about.
Unfortunately no very precise answer can be
supplied. We can only assume that the complex
and intricate relationship now manifested is the
final result of a long series of slight adaptations
through which insect and plant were mutually
specialized in such a way as to conform to each
other's needs.

It is impossible to conceive that any sudden
mutation of form on the part of the plant or of
habit on the part of the insect could have led to
so complicated an alliance.

The change must have been very slow and
gradual. First, we may suppose a condition in
which the ancestors of the yucca were sometimes
visited by the ancestors of the moth, but were not
dependent on them for any very complicated
method of pollenation. Then successive ages in

[201]

LUTHER BURBANK

which the moth gradually developed its special
pair of pollen-gathering jaws, while the plant
correspondingly shortened its pistil and became
more and more dependent upon the peculiar
process of fertilization to which the moth was
becoming adapted.

To any one who has not thought long and
carefully, with the examination of many examples,
along the lines of the evolution of organic forms
through natural selection, as explained by Darwin,
all this will probably seem rather vague and
unsatisfactory. And, indeed, it must be admitted
that among all the extraordinary cases of adapta-
tion through which insects and plants have come
to be mutually helpful, this is at least as difficult
to understand as any other.

The seeming intelligence of the act of gathering
and depositing the ball of pollen is emphasized by
the fact that this pollen is never of direct use to
the progeny of the moth, yet is vitally important to
them indirectly because it fertilizes the seed
embryos of the plant that are to serve them as
food. At first glance, then, one can scarcely escape
the thought that the moth must have had some
such comprehension of the plant's needs as that
which leads the human plant-experimenter to
cross-pollenize his flowers.

One might even be excused a momentary half-

[202]

Wild and Improved Dandelions

Mr. Burbank often experiments with our common

wild flowers, being always on the lookout for varieties that are

susceptible of improvement. His success in developing the familiar

dandelion is shown in this picture. The improvement was

made by selective breeding. Mr. Burbank thinks

that it may be possible to improve the stalk

and leaves of the dandelion until

it becomes an acceptable

garden vegetable.

LUTHER BURBANK

conviction that the insect must be endowed with
intelligence almost of the human order.

PLANT INTELLIGENCE

Such a thought is dispelled, however, when
we reflect on the seeming intelligence of plants
themselves and the apparently well-reasoned
schemes by which certain flowers ensure the
taking of effective toll of the insects attracted
by their nectar.

Even in the case of the yucca, it will be
observed that the plant was not quite a passive
partner in the arrangement through which the
perpetuation of its kind was assured. The pistil
of the flower had gradually been depressed below
the pollen-bearing anthers, in full confidence that
the moth would carry out its share of the
mutual compact. And when we reflect that this
conformation of stamens and pistil was doubtless
modified from an earlier arrangement less advan-
tageous to the plant, we are confronted with
evidence of a seemingly intelligent capacity to
adapt its structure to its needs on the part of the
plant that to some extent matches the apparent
intelligence of the insect.

Similar evidence of seeming design on the part
of flowers in the arrangement for guarding against
self-pollenation meets us on every side.

Consider, for example, the way in which the

[204]

LETTING THE BEES DO THEIR WORK

lilies project the receptive stigmas far beyond the
stamens; or the way in which the amaryllis, the
carnation, the balloon-flower, the geranium, and
numerous others effect the same purpose by
careful provision that the stamens and pistils of
any given flower shall not come to maturity at
the same time.

Then there are plants like the sage, the stamens
of which seem to lie in wait for the visitor; being
observed to bend quickly over, under stimulus of
contact, and rub their pollen on either side of the
insect's back. Again there is the milk-weed
(Asclepias cornuta), which stores its pollen in
tiers of hand-bags connected with a strap that
entangles the feet of the bees — and which, in its
over eagerness to make sure of the transfer of
its precious wares, sometimes defeats its own
purpose by so overloading the insect that it cannot
fly away.

There are water plants, too, that adopt methods
to secure cross-fertilization that are ingenious and
wonderful almost beyond belief.

Thus the little water plant called Villarsia
nymphoides sends out its flowers from its sub-
merged haunts as little detached balloons that
float to the surface of the water and then burst
open to offer their pollen to the insect messengers.

And the eel grass (Vallesneria spiralis), by an

[205]

LUTHER BURBANK

even more wonderful arrangement, projects its
pistillate flower up to the surface of the water on
a long spiral stem grown solely for that purpose;
while its staminate flower strains at the short stalk
on which it is tethered until it breaks away
and rises detached to the surface. The pistillate
flower, once pollen has been brought to it by the
insects from its floating mate, is drawn again
beneath the water by the recoiling stem, never
to reappear.

In the pre-evolutionary days, such instances
as these were cited as giving incontrovertible
evidence of design in nature.

But no one nowadays regards them in that
light, if we use the word in the old teleological
sense. Since Darwin taught us the way, we are
able to explain these marvelous adaptations; but
as evidences of the operation of the great principle
of natural selection they are no less wonderful.

And most remarkable of all, as viewed from
the present standpoint, are the orchids, the
extraordinary pollenizing devices of which were
first made generally known through the studies
of Darwin. A familiar illustration of the methods
adopted by this curious tribe is furnished by the
species known as Orchis mascula, which bears its
pollen in small bundles at the end of a slender
stalk, at the other end of which is a disc covered

[206]

LETTING THE BEES DO THEIR WORK

with a sticky secretion. An insect cannot secure
nectar from the flower without carrying away at
least one of these pollen stalks.

But the most remarkable part of the operation
is that, so soon as the insect withdraws from the
flower, the pollen stalk attached horn-like to its
head, bends over and curls itself into precisely
the position that will inevitably cause it to strike
the pistil of the next orchid that the insect visits.

Another species of orchid, known as Orchis
pyramidalis, grows two pollen bundles held
together by a sort of collar, with which it deco-
rates its insect visitor, clasping it, for example,
about the proboscis of a butterfly. Here as in
the other case the pollen-carriers adjust them-
selves in precisely the right position for the
deposit of their important burden; and in this
case the arrangement is such that a portion of the
fructifying powder is deposited on each of the two
pistils with which this species is equipped.
THE SENSES OF INSECTS

It is needless to multiply instances of the
wonderful adaptations of form through which
the various species of plants have made sure that
the insects for which nectar is provided shall
carry out their part of the bargain.

Some flowers have long tubes which only the
coiled proboscis of a moth or the slender bill of

[207]

LUTHER BURBANK

a humming-bird can fathom. These are sure to
provide pollen-carriers of a bulky character which
only humming-birds or large insects like the moth
could transport. Mechanisms may even be pro-
vided to exclude from the nectar chamber bees
and other small insects that could be of no service
to the flower.

But such cases, while in the aggregate numer-
ous, are on the whole very exceptional. In general
the plants with which the horticulturist deals, and
particularly the plants of the temperate zone, have
contented themselves with a much more simple
arrangement, whereby the pollen-bearers are so
arranged that any small insect that visits the
flower is sure to go away laden with pollen.

In particular, provision has been made by the
vast majority of flowers of the orchard and garden
to attract a single species of insect, the bee.

This familiar insect, the one member of its
vast tribe that is direclly helpful to man as a
producer of food, is the indispensable coadjutor
of the most important varieties of cultivated
plants. Bees of one species or another are the
universal distributors of pollen in orchard and
garden. The beautiful flowers that the apple and
plum and cherry put forth, and the perfumes they
exhale, are primarily designed as advertisements
for the bee and the bee alone.

[208]

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LUTHER BURBANK

Whoever realizes this truth will not be likely
to doubt that the bee, in common with other
insects, has good olfactory organs and an eye for
the discernment of color. Yet there have been
entomologists, even in recent times, who have
questioned whether insects really have the sense
of smell, and, others who have challenged their
color sense.

As to the latter point, whoever has taken
the trouble to observe the maneuverings of an
individual bee in the flower garden, and has seen
it pass from one red flower to another, confining
its visits exclusively to blossoms of one hue, will
have gained sufficient evidence that the bee is by
no means color blind.

As to the sense of smell, if further evidence
than that supplied by every-day observation of
the visits of insects to perfumed flowers were
required, it is furnished by an interesting and
remarkable experiment made by Professor Jacques
Loeb, formerly of California University, now of
the Rockefeller Institute in New York.

Professor Loeb placed a female butterfly in a
cigar box. Closing the box he suspended it in
mid-air between the ceiling and floor of a room,
and opened the window.

"At first," says Professor Loeb, "no butterfly
of this species was visible far or near. In less

[210]

LETTING THE BEES DO THEIR WORK

than an hour a male butterfly of the same species
appeared on the street. When it reached the
high window its flight was retarded and it came
gradually toward the window. It flew into the
room and went up to the cigar box upon which
it perched. During the afternoon two other males
of the same species came to the box."

A commentator observed that the experiment
makes it unequivocally clear that insects possess
an olfactory sense of almost inconceivable deli-
cacy. But the question as to what is the real
character of the stimulus that produces the sense
of smell, is one of the mysteries of science.

"A substance like musk," he says, "may give out
a characteristic odor continuously for an indefinite
period, while the substance itself appears to lose
no weight. If particles of the odoriferous sub-
stance are really thrown off, these particles must
be almost infinitely tenuous. If, on the other hand,
the stimulus is due to the giving out of waves or
vibrations comparable to the waves of light or of
sound, the nature and other characteristics of these
manifestations of energy are absolutely unknown."

Another experimenter has shown that ants will
follow a trail that has been made by other ants
bearing honey or sugar. The inference seems
obvious that the ants are following a very delicate
trail by the sense of smell. But perhaps it is well,

[211]

LUTHER BURBANK

considering the unrevealed nature of the stimulus
associated with odors, to adopt Professor Loeb's
cautious phrasing and speak of the sense through
which insects are guided to odoriferous objects as
"chemical irritability."

The fact that a bee is able to travel in a straight
line backward and forward between its distant
hive and the flower bed or the apple tree from
which it is harvesting, even though the distance be
a matter of miles, suggests the possession of organs
of sense of a far more delicate character than our
olfactory nerves.

It is hardly probable that vision is an important
aid in these long-distance flights; for Professor
Loeb's experiments have led him to infer that the
dioptric apparatus of insects is very inferior to the
human eye. Moreover the flowers would scarcely
find it necessary to put out expansive corollas and
deck themselves in gaudy colors if their signals
were meant for creatures having very acute vision.

In point of fact, the complex multiple eye of
the insect, devoid of any such adaptive apparatus
for focusing as the lens of the mammalian eye,
does not suggest acuteness of vision, but rather a
more or less vague appreciation of large masses
of color.

The recent experiments of Dr. Charles A.
Turner, of the St. Louis Academy of Science, have,

[212]

LETTING THE BEES DO THEIR WORK

indeed, demonstrated that bees can distinguish
between color patterns as well as between different
colors. But, although the tests of the naturalist
Plateau, which seemed to show that insects are
attracted solely by odor, are thus controverted, it
doubtless remains true that the sense of smell — or
some equivalent sense of a kind as yet unana-
lyzed — is the chief guide in bringing insects from
a distance to the vicinity of flower bed or fruit tree.

Professor Loeb declares that the "chemical
irritability" of the insect, as excited by odoriferous
objects, is immeasurably superior to the sense of
smell of human beings, and possibly even finer
than that of the best bloodhound. Observation of
the honey-gatherer making his "bee line" from
hive to orchard and back again prepares us to
accept this statement at its full valuation.

There must even arise a question as to whether
the insect's equipment of "chemical irritability,"
or whatever it may be called, does not amount to
the possession of a sixth sense.

AIDING THE BEE

We have instanced over and over the vital
importance of the process of cross-fertilization
which the bee accomplishes for the flower.

It may be of interest to cite a few familiar
illustrative instances of devices adopted by certain
familiar flowers to make the services of the bee

[213]

LUTHER BURBANK

surer and more effective. Inasmuch as the bee
has no conscious share in the plant's solicitude
to effect cross-fertilization, it has been found
expedient on the part of many flowers to adjust
the arrangement of stamens and pistils in such a
way that the visiting insect shall surely receive a
modicum of pollen, yet cannot rub this pollen
against the stigma of the same flower.

Some illustrations of what might be called
extreme measures to prevent such inadvertent
self-fertilization, were given earlier in the present
chapter. Let us note a few additional instances,
with reference in particular to flowers that are
largely pollenated by the bee.

A simple and effective method of guarding
against self -p oil enation we have seen illustrated
in the common geranium (Pelargonium).

When the geranium flower first opens, a little
cluster of anthers may be seen on the tip of the
erect filament in the center of the bright, showy
flower. At this stage the undeveloped stigma lies
closely folded up and wholly unreceptive among
the stamens. But soon after the pollen has been
shed or gathered, the anthers drop off; then the
stigma spreads out its five receptive lobes from
the tips of the connecting filaments, and is ready
to receive pollen from another flower.

In the snap-dragon flower, and in many other

[214]

Wild Flowering Peach, and Improved Variety

Nearly all wild forms oj plant life are susceptible of

improvement comparable to that shown in the above illustration.

Mr. Burbank is always on the lookout for variation among individuals

of a species. Wherever such variation occurs it may be accentuated by

selective breeding. As a rule further variation is stimulated by

hybridizing experiments. In making such an experiment, Mr.

Burbank usually has in mind many qualities. In such a

case as the above, for example, not only size and color of

blossom, but profusion and certainty of bearing

would be among the characters carefully watched.

LUTHER BURBANK

related plants, the anthers lie along the roof of
the corolla tube, where they are brushed by insects
that pass down the tube in search of nectar. The
stigma holds a similar position, but is farther out
toward the mouth of the tube. The stigma is a
very interesting structure; it is composed of two
flattened lips, which respond to the slightest touch.

When a bee, after visits to other flowers, enters
the tube, the hair-like appendages on its back
brush against the lower lip of the stigma, and the
irritation causes the lips to close tightly together,
coming thus in contact with and scraping the
pollen-dusted back of the bee.

Whether or not the receptive lips have secured
any pollen, they remain closed for four or five
minutes, so there is no danger that they will
encounter the bee as it leaves the flower laden
with a fresh supply of pollen from the companion
anthers. But a few minutes later the stigma lobes
open again, like a trap set for the next visitor.

Human ingenuity could not well devise a
mechanism better adapted than this to secure
cross-pollenation and ensure against the possi-
bility of self-fertilization.

The foxglove (Digitalis) also has stamens and
pistils lying along the roof of the corolla tube. Its
device to prevent self-fertilization is the less
ingenious but equally effective one of ripening

[216]

LETTING THE BEES DO THEIR WORK

the stigma only after the pollen has been dis-
charged— an expedient which, as we have seen, is
very commonly resorted to by other species of
plants, including the lilies.

The Spanish broom (Spartium junceum) is a
typical butterfly-like flower, that, in common with
others of the same family, has developed a peculiar
mechanism to bring about cross-pollenation. The
two lower petals are joined together into a keel-
shaped structure that connects the stamens and
pistils. The other three petals are more enlarged,
and are spread to make a more effective advertise-
ment, challenging the attention of insects. The
visiting bee naturally alights upon the projecting
keel. The weight of its body presses this down-
ward and the stamens and pistils, by a spring-like
action, are thrust out against the body of the
insect, scattering the pollen freely.

Thus the stigma may become covered with
pollen that the bee has received from some other
flower while the anthers supply a new coat of
pollen for future distribution.

Still a different arrangement is that of the
common iris. Here the anthers lie in a fold of
the large petal-like branches of the style. The
stigmatic surface is confined to a little crescent-
shaped patch near the tip of the style-branches,
and is protected by a thin, sack-like shield. The

[217]

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LETTING THE BEES DO THEIR WORK

structure of the flower is such that an insect as
it passes down the petals on its way to the nectary,
brushes against the anthers, and dusts off the
pollen. As the insect passes out, the stigma-shield
protects the stigmatic surface completely.

But as the insect visits another flower, its
pollen-covered back comes in contact with the
edge of the stigmatic shield and the pollen is
scraped off against the receptive surface.

These, then, are familiar illustrations of the
really wonderful adaptations through .which it
comes to pass that the bees carry out their part
of the ancestral compact that ensures the plant
such interchange of pollen as is essential to racial
progress. Perhaps the most alluring feature of
the entire coalition is that the bee performs its
all-important function unwittingly in the course
of the quest of sweets that appeal to its appetite.
There is no compulsion in the matter; the plant
depends upon the more powerful influence of
persuasion.

And to add to the satisfactoriness of the entire
arrangement, from a human standpoint, it must
be recalled that the efforts of the industrious
insect, which thus make possible the work of the
plant experimenter, result at the same time in
storing the nectar gathered from the flowers to
form one of the most delectable of foods.

[219]

Patagonian Squash

The members of the squash tribe are readily fertilized,

as illustrated in earlier pictures of this volume, but the hybrids

tend to show extreme variation, and they are very difficult to fix. Mr.

Burbank has shown, however, that it is not impossible to fix

The

new varieties by carejul selective breeding.

here shown was developed from seed sent Jrom

squash

South America,
and weight

It has almost the solidity
oj a cannon ball.

FIXING GOOD TRAITS

How TO HOLD A RESULT
ONCE ACHIEVED

IT IS traditional that you cannot teach an old
dog new tricks. The maxim applies with full
force to old plants. You may bend the twig
and make a permanent twist in the future tree;
but the hardened stock of the matured branch
will return persistently if bent, and will break
rather than change its form.

Now there is something like the same differ-
ence in flexibility between yoilng and old races of
plants. Here is a variety of plant that has been
developed in the orchard or garden, under man's
influence, in the course of the past few generations.
It tends to vary, and its progeny may be made
to adapt themselves to different conditions; by
selection, they may be developed into divers and
sundry new races.

But yonder palm tree has no such propensity
to vary. Its ancestors have remained substantially

[VOLUME III— CHAPTER VII]

LUTHER BURBANK

unchanged, true to their racial type, generation
after generation, for untold centuries. It repre-
sents an old, fixed, conservative stock. No one
knows how to make it change, except within the
narrowest of limits.

There is a very essential time element, then,
that is instrumental in determining the fixity or
variability of a race of plants. A plant that has
been bred true to a given type for long periods
of time, as is the case with the generality of wild
plants, will breed substantially true from seed,
and as a rule will maintain its racial type even if
transplanted to new surroundings.

But, on the other hand, the generality of
cultivated plants are of mixed ancestry. Man has
attempted within recent generations, to change
them and adapt them to his needs. He has
constantly been hybridizing them, or placing
them under conditions that resulted in their
hybridization through the visits of bees; and he
has selected and cultivated the individual speci-
mens that tended to vary, and thus has fostered
the habit of variability rather than that of fixity
of character.

In the case of most orchard fruits, as we have
had occasion to observe more than once, so many
strains are blended that propagation from seeds
is quite out of the question; unless, indeed, it be

[222]

FIXING GOOD TRAITS

desired to secure seedlings of varying qualities in
the interests of experimentation, or in the attempt
to develop still other varieties.

One might plant a thousand acres with seeds
of the Baldwin apple, without perhaps producing
a single plant that would precisely duplicate the
qualities of the fruit from which the seeds were
taken. And the same thing is true in greater or
less measure of the majority not merely of orchard
fruits but of cultivated plants in general.

The notable exceptions are annual plants that
are habitually grown from seed, such as melons
and peas in the garden, and the great tribe of
cereals represented by wheat, oats, rye, and barley.
The reason why all of these breed true from seed
is that they are necessarily propagated in this way
alone, and it has been essential that fixed races
should be developed.

Mankind depends largely upon the cereals for
food, and his existence would be altogether pre-
carious could he not have reasonable assurance
that when he sows grain of a certain quality, he
will secure a crop of grain of similar quality.

The fixity of character of the cereals and
various other plants, including peas, and beans,
is enhanced and assured by the fact that the
flowers of these plants are habitually self-
fertilized. If you examine a head of wheat at

[223]

LUTHER BURBANK

the right stage, you will find that you must pull
open the little bracts in which the flowers are
encased, in order to make the stamens and pistils
visible. Under ordinary circumstances, insects
cannot find access to them. The wind has no
influence over them. Their normal habit is to
fertilize the pistil of each individual flower with
pollen from the stamens that grow within the
same closed receptacle.

This is inbreeding of the closest and most
intimate character, and there is obviously no
ordinary opportunity to introduce the element of
variability which, as we have seen illustrated over
and over, cross-fertilization brings.

So the essential qualities that make wheat
valuable have been aggregated in a few fixed
combinations, and the resulting varieties of wheat,
differing not very widely from one another, are
never crossed, unless by artificial means to meet
the special needs of the plant developer.

They remain fixed because they are of pure
lineage.

MIXED ANCESTRY AND INBREEDING

The case of the wheat is typical. Its develop-
ment furnishes an illustration of the method
through which many specialized races of animals
and plants under domestication have been devel-
oped. Indeed, it might almost be said that the

[224]

FIXING GOOD TRAITS

one rule that has actuated the developer of special
races has been to apply the principle of inbreeding.
When an individual appeared in a herd or flock
that showed certain peculiarities that the owner
thought desirable, the natural and obvious way
of perpetuating these was to breed from that
individual; and then persistently, for a time, to
inbreed the progeny in order to accentuate the
desired trait.

The result has often been all that could be
expected. Take, for instance, the case of the
trotting-horse.

It is, I believe, a matter of record that
practically the entire stock of trotters, as developed
in America in the past hundred years, descended
from a single ancestor, the celebrated "Messenger."
This individual horse chanced through some
accidental mixture of ancestral strains to combine
in its organization the particular qualities of nerve
and muscle that adapted it for rapid progress by
trotting instead of by the more natural method of
running:

And as regards this quality or combination of
qualities, the horse proved amazingly prepotent.

Its descendants soon constituted a race of
trotters. Pedigrees were kept; the best individuals
of the new race were selected as breeders; closely
related animals were mated; and the character-

[225]

LUTHER BURBANK

istics that make for speed at the trotting gait were
in a few generations so fixed that a new race of
horse was produced.

The principle thus illustrated applies with
equal force to the breeding of plants. Indeed, it
is possible here to hold even more rigidly to the
idea of inbreeding, inasmuch as the individual
flowers may be self-fertilized. We have just seen
this illustrated in the case of the wheat and allied
cereals.

There is no question whatever that any given
characteristic of a plant, once it appears, can be
accentuated and fixed, first in individuals, and
finally indelibly in the heredity of the descendants
of the plant by systematic inbreeding.

But, unfortunately, there are complications in
the case of most experiments that the originator
of new plants is called upon to undertake, that
robs the method of its simplicity. The com-
plications arise from the fact that the would-be
originator of new races of fruit or flowers is
usually seeking to develop not merely a single
quality, but a number of qualities. And this alters
the case fundamentally.

In the case of the trotting-horse, the one all-
essential quality desired is speed.

The capacity to trot a full mile at high speed
does, indeed, imply the possession of stamina and

[226]

FIXING GOOD TRAITS

courage, as well as capacity for rapid action of
the legs. These are qualities that are necessarily
linked with the capacity for the right kind of
muscular action.

But beyond this there are very few qualities
upon which the breeder must insist. It does not
greatly matter whether the speedy animal is small
or large; its color is mostly a matter of entire
indifference; and it is taken as a matter of course
that the record-breaking animal will be nervous
in temperament, tender as a hothouse plant, and
requiring such care and attention as would be
only wasted upon a more plebeian animal.

In a word, the breeder of trotting-horses fixes
attention principally on the single quality of
speed.

But it is rare indeed that the would-be
developer of a new plant can thus fix attention
upon any single quality to the disregard of other
qualities. On the contrary, as a rule, the plant
experimenter, while he may have in mind one
most important quality, must consider at the same
time six or eight or ten or a dozen other qualities
that are only a degree less essential. We have
seen this illustrated again and again, and we
shall have occasion to recall some of the specific
characters involved in the course of the present
discussion.

[227]

LUTHER BURBANK

In reality, the task of the experimenter who
would develop a new and really valuable variety
of plum or cherry or apple or spineless cactus, is
to be compared not with the task of breeding
trotting-horses as they are, but rather to the
task that would confront the breeder were he to
attempt to develop a race of trotting-horses which
should retain the capacity to trot a mile in less
than two minutes, yet at the same time should be
big and powerful enough to serve on occasion as
draught horses; should be always of some pre-
determined color, say bright bay; and should be
as hardy and require as little attention as the
toughest broncho.

It requires no great amount of imagination to
see that the task of breeding race horses would
be quite different from what it is, were the
specifications such as these.

Yet I repeat that the qualities that the plant
experimenter usually seeks to combine in his new
variety of flower or fruit are at least as varied and
as difficult to fix in combination as the qualities
just suggested for the supposititious new breed of
race horses.

THE SHASTA ON THE WITNESS STAND

Let us by way of illustration recall the case of
the Shasta daisy which, the reader will remember,
was developed by the union of three different

Rose Cuttings — Developed by Selective Breeding

A new variety of rose — developed by selective breed-
ing— may be propagated by merely cutting the branches into
sections, and planting them in the way illustrated on page 135. It is
oj course necessary to have at least one bud, and preferably
two or three, on each cutting. Mr. Burbank has devel-
oped some very remarkable new varieties of roses,
including one that received a gold medal
at the St. Louis International
Exposition in 1904.

LUTHER BURBANK

species of flowers, coming respectively from
Europe, America, and Japan.

It will be further recalled, that the ideal daisy
that I had in mind for years before it became an
actuality, showed in superlative degree a consid-
erable variety of qualities that were not found in
combination in any one of its ancestors. Indeed,
the Shasta daisy, as ultimately developed, reveals
a number of very conspicuous and important
qualities that are not shown at all in any one of
its known progenitors.

To make the illustration specific, we may cite,
among the qualities that are assembled in the
finished product, the following: (1) extreme size,
(2) dazzling whiteness, (3) broad rays, (4) double
rays, (5) gracefully drooping rays, (6) keeping
quality of flower, (7) smooth stem, (8) early and
persistent blooming, (9) hardiness, (10) constant
bearing.

The perfected Shasta daisy manifests these
qualities in supreme degree. As regards each and
every one of them, it surpasses any of the parental
forms from which it sprang; indeed, as to some
of them, such as double and drooping rays, it
shows an entire departure from all of its observed
ancestors, harking back to the remoter forms of
past ages.

But to assemble these qualities in a single

[230]

FIXING GOOD TRAITS

flower required about fifteen years of persistent
effort, and the handling of probably not less than
half a million individual seedlings.

Generation after generation the plants were
cross-pollenized and selected over and over, always
with an eye not merely to a single quality, but to
the ensemble of qualities.

And always we were confronted with the
difficulty that in reaching out to bring in some
new quality, we were disturbing the balance of
qualities already attained, and endangering the
entire structure.

When, for example, the final cross was made
with the Japanese daisy, to secure if possible the
element of whiteness shown pre-eminently by that
flower, and add it to our mosaic, we, of necessity,
brought in also from the Japanese parent, along
with the quality of whiteness, such undesired
qualities as crude, ungraceful stems and flowers.

It was necessary to select and interbreed, and
select again, for successive generations from
among a multitude of the progeny of this cross,
before a plant was finally secured that presented
the desirable combination of qualities, retaining
the whiteness of the Japanese parent, but rejecting
its undesired characteristics of leaf and stem, and
departing utterly from that particular parent in
point of size.

[231]

LUTHER BURBANK

But, although an individual was at last found
that did combine all the desired qualities, the very
fact that this individual had been built up by
putting together this quality brought from one
parent and that quality from another, with the
rejection of antagonistic qualities in each case,
makes it inevitable that the perfected Shasta
should contain latent in its system a whole
coterie of tendencies which are fighting for recog-
nition, and which will make themselves felt in
subsequent generations.

Hence it is that when seeds are gathered from
the perfected Shasta they will not give us a crop
of flowers like their parent. On the contrary, they
will show the utmost diversity of form and size
and color, making tangible thus the persistent
force of the hereditary tendencies that had been
transmitted from divers ancestors, but which
were submerged or made latent, simply because
they were momentarily subordinated to opposing
qualities, in the case of the perfect Shasta.

The Shasta daisy, then, while individually
almost a perfect embodiment of the ideal at which
I aimed, is when reproduced, from seed, anything
but a fixed type. Had it not been possible to
propagate the plant by division and then by an
unending series of successive divisions to produce
an indefinite number of individuals, each precisely

[232]

FIXING GOOD TRAITS

like the original because they were in a sense
a part of it, my entire series of experiments
in developing the new daisy would have been
unavailing except for still further selection. But
as the case stands, it was possible rapidly to
develop an entire race of Shasta daisies by
root-division, and thanks to this method the
descendants, or, to speak somewhat more accu-
rately, the sisters of the original Shasta daisy have
become an enormously populous race, scattered to
the remotest parts of the earth.

Several other types of Shastas have been
developed by new breeding experiments from the
original stock, but to this day the race of Shasta
daisies must be propagated from the root, and not
grown from seed, unless one desires a conglom-
erate progeny, departing in many ways from the
form and quality of the immediate ancestor.
FIXING A TYPE

In all this, it must be recalled, the Shasta daisy
does not differ from a large number of long-
established cultivated plants that are everywhere
recognized as being "fixed" races.

One does not produce apples or pears or
cherries or plums or blackberries or potatoes or
sugar cane or horse radish, to say nothing of roses,
ornamental shrubs and a great number of flower-
ing plants, from seed.

[233]

Wild Grapes

There are a good many species of wild grapes, and

Mr. Burbank has utilized several of these in his experiments.

His chiej work with this species has been done, however, with the

common European cultivated grape, which has developed a large

number oj varieties through being selected Jor various purposes

during past centuries. In particular some oj his most

important new varieties are descended Jrom a "bud

sport," — that is, a variation that appeared

"spontaneously" in a branch growing

on an ordinary grape vine.

FIXING GOOD TRAITS

They are propagated by grafting or budding,
or by rooting the stem or dividing the roots or
planting the tuber. And the reason in each case
is the same. The perfected variety originated
from a single individual that combined a large
number of desirable qualities, and the entire
company of individual representatives of that
variety, though they be numbered in millions,
are not really descendants, but offshoots, of the
original individual.

Each cion or bud from a given tree will
produce fruit precisely like that from the tree
from which it is taken, because it is itself a part
of the tree. And however widely new cions and
buds from the first cion may be disseminated,
they carry the same traits, because, rightly con-
sidered, they are a part of the same individual
organism. The Seckel pear tree that grows in
your dooryard is, from the standpoint of heredity,
a tree of the same generation with untold thou-
sands of other Seckel pear trees that have grown
here and there across the hemispheres for more
than a hundred years — or since the first one
appeared in the orchard of the Pennsylvanian
whose name they bear.

Were it not for the contradiction of terms, one
might say that all Seckel pear trees constitute a
single tree.

[235]

LUTHER BURBANK

All these Seckel pear trees are essentially
alike; they bear fruit that may vary in size and
lusciousness with varying conditions, but that is
everywhere essentially identical in flavor and in
the characteristic qualities of texture and color.
But if you plant the seeds of one of these pears
you do not secure Seckel pears, unless by the
merest chance, among the progeny. You secure
instead, representatives of a galaxy of ancestors,
no one of them individually just like the Seckel,
although collectively they represent all the
qualities of that fruit, plus almost numberless
undesirable qualities.

PAIRS OF QUALITIES

The fact that our most familiar and best prized
fruits and flowers show this lack of fixity, suggests
that the inherent difficulties in the way of fixing
the type of these plants so that they will breed
true from seed are very great. Otherwise some
one would long ago have remedied the defect, for
the advantages of being able to grow these useful
plants from seed are obvious.

Nevertheless it should not be assumed that the
task of fixing the type of a newly developed race
of fruit or flowers is of necessity a hopeless one.

The truth is that it would be possible to fix the
type of almost any variety of plant, provided time
enough and patience enough were devoted to the

[236]

FIXING GOOD TRAITS

task, and the experiment were conducted on a
wide enough scale. Indeed, nothing more would
be necessary than to continue for an additional
number of generations the same line of experi-
mentation through which the new varieties were
produced; attending carefully at all stages to the
analysis of the different qualities that prove to be
mutually antagonistic.

To this end, the new terminology which
endeavors to analyze the qualities of a given
plant into complementary pairs of unit characters
may prove very helpful, particularly to the inex-
perienced investigator.

Such an analysis has always been made, tacitly
at any rate, by the successful plant experimenter.
No one can think of the development of an early-
fruiting cherry or prune without having in mind
the quality of /afe-fruiting. To speak of a prune
with high sugar content implies one with low
sugar content.

In a word, the desired quality of fruit or flower
at which one aims is always balanced against
the opposing quality — sweet fruit against sour,
hardiness against tenderness, resistance to disease
against susceptibility to disease, profuse bearing
against scant bearing, thorny brier against smooth
brier, black fruit against white fruit, and so on
down the list.

[237]

LUTHER BURBANK

It is only by constantly bearing these divergent
pairs of qualities in mind that any experimenter
can hope to advance toward the production of an
ideal fruit or flower or vine. And it has always
been so.

OLD WINE IN NEW BOTTLES

But there can be no question that the new
terminology, as used by present day biologists,
serves to give precision to the ideas of the plant
experimenter, and enables him to analyze the
results of his experiments in more precise terms
than have hitherto been available.

It will be convenient, therefore, and probably
helpful to the reader, in making precise reference
to some of the experiments in plant breeding
already detailed, with special reference to the
possibility of fixing the type of new races, if we
discuss the matter in the new terminology.

It will at once appear that when a plant
developer attempts to fix a certain type, he is
fundamentally changing his point of view. Hith-
erto he has been concerned to make plants vary,
in order that he might seize on new forms, and
use them as material for developing the type at
which he aims. And his success in developing a
new race is largely dependent upon the extent to
which he has been able to induce the plants with
which he experiments to vary.

[238]

Seedless Grapes

This shows one oj Mr. Burbank's choicest varieties

oj new seedless grapes. They have been developed by selection,

and are oj delicious quality, with an added attractiveness due to the

entire absence oj seeds. Of course a fruit thus developed must

be propagated by cuttings, and is not susceptible

of Jurther improvement, unless there

should be a reversion to the

seed-bearing condition.

LUTHER BURBANK

So now, when he attempts to restore fixity to
something that he has purposely made unstable,
he is at once confronted with the danger of
undoing much that he has accomplished. The
measure of success that he can hope to attain
will depend very largely upon the particular kind
of unit characters that he has combined in the
product that he now wishes to make stable.

We have seen that, as between the opposing
members of any pair of unit characters, it is
usually discovered that one has prepotency or
dominancy over the other. When blackberries
of normal color, for example, are crossed with
the white blackberry, the progeny are all black,
because this color is the dominant member, and
white the recessive or negative member of the pair
of unit characters. But we saw also that the
recessive trait will reappear in the succeeding
generation, and that when it does reappear, it will,
within certain limits, thereafter breed true.

So, when in the second generation we again
produce a white blackberry, we have a type which
is fixed as regards the particular character of
whiteness. In other words, our white blackberry,
even though both its parents, and one grandparent,
were black, may be considered a berry of pure
white strain. From the moment of its appearance
it is a fixed type as to color.

[240]

FIXING GOOD TRAITS

But, unfortunately, it is not sufficient that the
white blackberry should breed true as regards the
quality of whiteness alone. There are other quali-
ties of size and flavor that are equally essential.
And these, it would appear, include sundry other
pairs of unit characters — sweetness versus sour-
ness, large size versus small size, profuse bearing
versus scant bearing, and the like — that are repre-
sented in our berry by mixed factors.

In the Mendelian view, it will be recalled, there
are always two factors representing any pair of
unit characters.

In the case of our white blackberry, in the
Mendelian view, both factors for the unit char-
acter blackness-versus-whiteness are of the white
order; or in the technical phrase, the berry is
"homozygous" for that pair of factors.

But as regards, let us say, the factor for the
unit character bigness-versus-smallness the case is
different; for this character may chance to be
represented by one factor of each type. In other
words, resorting again to the technical language,
the berry may be "heterozygous" as regards that
character.

In this particular generation, the quality of
bigness prevails, because bigness is dominant to
smallness. But the factor for smallness must have
a hearing in the next generation.

[241]

LUTHER BURBANK

Until we can produce a white blackberry that
is "homozygous" for size-factors as well as for
color-factors, we shall not obtain a fruit that will
breed true to size as well as color.

A similar analysis might be applied to the
various other pairs of unit characters that are
represented in any given fruit or flower. And the
essential principle, stated in Mendelian terms, to
be aimed at by the experimenter who would fix
a newly developed type of plant so that it will
breed true from seed, must be to render the plant
"homozygous" for the factors of each pair of unit
characters involved. If that can be done, the
plant will breed true; if that cannot be done, the
plant will not breed true.

In the olden phrasing, this would be spoken of
as "line" breeding — a method long familiar to
every breeder of plants or animals.

FIXING A TYPE IN THE SECOND GENERATION

In actual practice, where only two or three
unit characters are involved, it may be possible
to produce a new type that breeds true, or is fixed,
in the second generation. In such a case the time
element may be ignored. ,

Take, by way of illustration, Professor Castle's
guinea pigs, to which reference has more than
once been made. Suppose we have as parent
stock a black guinea pig with a smooth coat, and

[242]

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LUTHER BURBANK

a white guinea pig with a rough coat. Now we
have already seen that blackness is dominant to
whiteness as regards the coat of the guinea pig,
and we must further understand that roughness
of coat is known to be dominant to smoothness.

We must expect, then (according to Professor
Castle), that when a cross is made, the guinea pigs
of the first filial generation will, unlike either
parent, be black in color and rough as to coat.

But, in the succeeding generation, the black,
rough-coated guinea pigs being interbred, there
will be a certain number of offspring that combine
the dominant characters of blackness and rough-
ness of coat, and will breed true to these; a certain
number will be black and rough-coated, but will
bear the latent characters of smoothness and
whiteness of coat which will reappear in their
progeny; and, finally, there will appear individ-
uals combining the two recessive traits of white-
ness and smoothness of coat.

These white, smooth-coated individuals are
obviously different from their parents, and
different also from either of their grandparents.
They constitute a new race, sprung into being in
a single generation, and a race that will necessarily
breed true as to the character of smooth coat and
white coat, because they are "homozygous" as to
the factors for both these recessive characters.

[244]

FIXING GOOD TRAITS

Their progeny cannot be black because their
germ-plasm contains no hereditary factor for
blackness; nor can their progeny be rough-coated,
because their germ-plasm contains no hereditary
factors for rough-coatedness.

Yet side by side with this new fixed race of
smooth-coated white guinea pigs, there are, as
we have seen, twins of the same fraternity that
instead of being white and smooth in color, are
black and rough. And these also constitute a
new race that will breed true because they
contain, as regards the unit character for color
and for condition of hair, only the dominant
factors of blackness and roughness. They also
are "homozygotes," but they are of the opposite
type — dominants instead of recessives.

Meantime, we must not overlook the other
members of the fraternity, twin brethren of these
new races, which are individually black and
rough, but which are "heterozygotes" as regards
the unit characters under consideration, and hence
will show progeny of variously mixed character-
istics as to roughness or smoothness of coat, and
as to black or white color.

This illustration, perhaps, gives as tangible an
impression as can well be gained, of the com-
plexities that confront the experimenter when he
attempts to fix a new type of animal or plant.

[245]

LUTHER BURBANK

Even where only two unit characters are
involved, the progeny of the second generation,
as we have just seen, may break up into numerous
races, some fixed and others variable. And, as
we have previously pointed out, the complications
thus introduced increase at a startling ratio when
more characters are under consideration.

Moreover, the matter is rendered increasingly
difficult for the plant experimenter by the fact that
he must often wait, particularly in the case of
orchard fruits, for a term of years before he can
know the result of any single breeding experiment.
To sort out the pure types from the mixed ones of
any given generation under these circumstances
becomes a matter of enormous complexity.

It could be done, by inbreeding representatives
of the new type and carefully selecting the progeny
for a series of generations.

But in the end, all that would have been accom-
plished, in the case say of a Shasta daisy or of a
stoneless plum or a sugar prune, would be the
production of seed that could be used to dissemi-
nate the new variety. And in most cases we are
justified in feeling that this would represent an
undue expenditure of time and energy for a com-
paratively insignificant result.

For, as the case stands, even though the new
form will not breed true from seed, it may be

[246]

FIXING GOOD TRAITS

propagated indefinitely from roots or from the
grafting of cions; so that in practice the failure
to breed true from seed has little significance.

Probably it is the fact of the relative unimpor-
tance that our cultivated plants should breed true
from seed that chiefly explains the failure of plant
breeders in the past to fix the type of the best
known fruits and vegetables and flowers.

The same reasoning obviously applies to the
newly developed varieties. While so much work
remains to be done in the way of developing
new types of fruit and flower, the most practiced
experimenters will probably feel that they have
not time and energy to spare for the fixing of the
new races already developed.

We shall have occasion to call attention to
various exceptions to this rule in the course of
our subsequent studies; particularly with refer-
ence to certain annual plants. Here by "line"
breeding for a few generations we may fix the
new traits almost as firmly as the old traits are
fixed in wild species. Again we shall learn in due
course of new hybrid fruits like the sunberry, the
primus berry, and the phenomenal berry that are
fixed as to their chief properties from the very
first hybrid generation. But as regards most of
the new forms of fruit and flower that we have
hitherto described, the rule holds with full force.

[247]

Label on Tree Graft

This illustrates Mr. Burbank's method oj labeling a

graft, in order to keep track of his experiments. The label is

of wood, and the inscription is made with paint or pencil. The wire

attaching the label should of course be loosely applied

to avoid restricting the plant.

RECORDING THE EXPERIMENTS

EASY WAYS TO KEEP TRACK
OF PROGRESS

EVERY ONE has heard the story of the
distinguished professor who devoted his
entire life to the study of a particular
species of mite, and who, on his deathbed,
regretted that he had not confined his attention
to the study of the respiratory organs of this
insect, instead of trying to comprehend its entire
structure.

This specialist, like many another, felt that he
had wasted his energy by attempting to cover too
wide a field. He felt that his ten volumes or so
on the anatomy of the mite could give but super-
ficial treatment of a great subject.

Whoever sympathizes with the attitude of mind
revealed by this doubtless apocryphal yet truly
symbolic tale, will have scant patience with my
method of plant experimentation. For, far from
confining attention to a single species, or even to

[VOLUME III— CHAPTER VIII]

LUTHER BURBANK

a single genus or order, I have extended my
observations to almost every form of plant, testing
species by thousands, and individual specimens
by hundreds of thousands or millions, in my
experimental gardens; and only by exception has
complete record been kept of all details of any
given series of experiments, beyond the more or
less fallacious records of memory.

Yet I have had the good fortune to produce, I
suppose, more forms of plant life that could justi-
fiably be called new, than have been produced by
any other single experimenter in our time. Had
I stopped to make meticulous record of each
experiment, I doubt if I should now know more
than I do about even my less important products,
and I surely should have been able to produce
only a fraction of those that I have produced.
METHODS AND RESULTS

Yet it must not be supposed that I have alto-
gether refrained from graphic recording of the
progress of my tests. The fact is quite otherwise.
I have kept in the aggregate a vast body of records,
and have had them always at hand, under my eye
from day to day, telling of the essentials of my
hybridizing and other experiments.

My "plan books" have been a constant aid to
memory, and guide to further effort.

My record books have set down in black and

[250]

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LUTHER BURBANK

white the unequivocal evidence of progress — or
of failure to progress. Few salient facts as to
the precise parentage of important hybrids and
the exact methods by which variation has been
brought about have failed to find explicit record,
notwithstanding the omission of multitudes of
details that to some observers might have seemed
worthy of transcription.

And if I have adopted in the field shortcut
methods of recording selection, these have not
lacked precision and accuracy, notwithstanding
their time-saving character.

In point of fact, all along the line I have
endeavored to strike a happy medium between
the waste of time that would result from the
keeping of unduly elaborate records, and the
waste of effort that would necessarily result if
no records at all were kept.

The reader who would clearly comprehend the
nature of the compromise must bear in mind that
I have, as a rule, had a practical object in view
in conducting my experiments. It is true, as
Professor Bailey has courteously said, that I
constantly make experiments with plants for the
mere love of the work. It is true also that my
tests include hundreds of species from which I
expect no very definite return. Yet it is further
true that the main body of my experiments have

[252]

RECORDING THE EXPERIMENTS

been concerned with flowers or fruits that seem
to offer opportunities for practical improvement.

I have usually been seeking, in the experiments
to which most time has been given, to modify the
plant in such a way as to make it a more beautiful
and desirable garden ornament, or to modify a
vegetable or fruit in such a way as to make it a
more valuable food product.

Such being the case, it will be understood that,
with regard to large series of experiments, I have
been concerned with results rather than with
methods. As to the latter, it often happens
that numberless experiments might be described
in substantially the same terms. Once the prin-
ciples of hybridization and selection have been
clearly mastered, they may be applied to almost
every variety of plant life. There are differences
in the detail, but the broad outline is the same for
each.

ESSENTIALS VERSUS NON-ESSENTIALS

It would then be but a waste of time to record
over and over details as to these broader outlines
of plant experimentation. Where anything of
interest has appeared, any point as to which a
plant shows differences from its fellows, this has
become a matter for recording.

Moreover, it has been my universal custom to
make record of the first hybridizing or crossing

[253]

N^^^_".^. • V

^fe— " ^

Diagram o/ Tree Grq/is

TAis is a leajjrom Mr. Burbank's plan book. It is
a sort o/ shorthand or diagramatical record that condenses a
large amount o/ information into small space, leaving room /or
fiona/ records should they be called /or. Suc/r a page
seems cryptic to the casual observert but to
Mr. Burbank himself it is
full oj meaning.

RECORDING THE EXPERIMENTS

through which any particular series of experi-
ments is inaugurated. The parentage of the
Shasta daisy, the white blackberry, the stoneless
plum, the sugar prune, the plumcot, the thornless
blackberry, the spineless cactus — these are matters
of clearest and most unequivocal record. The
results of the first crossing, through which matters
of prepotency and of latency are determined, and
through which the plant is given the impulse to
variation, are also explicitly shown.

But when, particularly in case of a fruit
having complex characters, the experiment passes
to stages of the third and fourth generations,
involving tens of thousands or hundreds of thou-
sands of seedlings, it is no longer possible to make
detailed and explicit record, with exact count of
the different combinations and variations devel-
oped, for two very explicit and sufficient reasons.

One reason is that the numbers of seedlings
involved are so great that it would be physically
impossible for any one carrying on hundreds of
different series of tests at the same time to make
numerical count in accordance with the statistical
method adopted by workers who are experi-
menting on a limited scale.

The second reason is that even if such a count,
showing the exact number or percentage of seed-
lings with different combinations of traits, were

[255]

LUTHER BURBANK

attempted, it would be unavailing unless vast
companies of seedlings were preserved for the
term of years necessary to bring them to fruitage.

When one is concerned solely with numbers,
or with such tangible qualities as color of hair in
the case of Professor Castle's guinea pigs, or color
of feather with Professor Davenport's fowls, it
is an easy matter to check results, because the
creatures under investigation manifest the quali-
ties that are being tested from the moment of
birth, or develop them at a very early age.

But with plants the case is obviously different.
Whereas we may judge something as to the
character of fruit that a seedling will ultimately
bear from observation of the seedling itself, yet
for purposes of scientific record such predictions
would be considered as worse than worthless.
To know what percentage of seedlings of a given
generation have really progressed toward the ideal
of a sugar prune that will ripen August 1st instead
of September 1st, let us say, it would be necessary
to let all the seedlings grow for several years, or
at the very least to wait two or three years for
the grafted cions from each seedling to come to
fruitage.

The practical experimenter, seeking results,
cannot possibly work in this way when he works
on a large scale.

[256]

Record o/ Blooming

Facsimile of another page from Mr. Burbank's
record books. This one has to do with the time o/ blooming of
various Jruit bearers, — a matter of great importance, because blossom-
time is correlative with the time oj Jruiting, which often has
important bearing on the value of a new fruit. It is
a little surprising to learn that varieties
that bloom early ripen their fruit
relatively late, and vice versa.

LUTHER BURBANK

He must be content to select from among
thousands of seedlings the one or five or ten or
fifty that appear to him most promising. To these
he must pin his faith, and all the rest must be
destroyed to make room for other plants.

Otherwise he would require not twenty odd
acres, which make up the total area of my experi-
mental farm, but hundreds or even thousands of
acres.

And to keep track of the multitudinous
seedlings would require the aid not of the half
dozen or so assistants whose cooperation makes
my experiments possible, but of a small army of
equally industrious workers.

SYSTEMATIC WORK IMPERATIVE

But, having thus outlined the limitations that
necessarily attend work conducted on a large and
comprehensive scale, let me now proceed to elab-
orate somewhat the other side of the story.

Let me outline the various practical methods
of recording experiments that have been devel-
oped in the course of my years of experience.
Let me in particular point out some of the short-
cuts that have made it possible for me to record
the essentials, and even in important cases the
details, of progress, with a minimum expenditure
of time and labor.

Among the essentials that cannot be overlooked

[258]

RECORDING THE EXPERIMENTS

by any systematic and successful experimenter are
the following:

A general plan of the ground occupied by all
the experiments must be made, and there must be
clear record of each plant, shrub, or tree planted.
It is important also to record the time when each
one was grafted or budded; the date of all experi-
ments in crossing any particular tree or plant;
observations as to any anomalies of development;
and finally, as a matter of course, the results
obtained.

As to these things, the memory, no matter how
tenacious, must prove more or less untrustworthy.
It is only the black and white record that can be
depended upon. But plans may be outlined so
simply that all these essentials may be recorded
at the expense of very little time or labor.

It is not much trouble, for example, to keep a
plan book at hand, each page of which is devoted
to a certain planting, its location on the grounds,
and all other matters that are worthy of record.
It will facilitate matters in such a book to have
the records of planting arranged somewhat in
the order in which the plantings have occurred
during the season.

If these records are made on large sheets of
paper so plotted as to show the location of the
various beds of plants, this will be an added

[259]

Grafting Record

Yet another page of Mr. Burbank's record books, this
one dealing with grafting. It will be seen that the records oj
different years are associated, and it will be obvious that the records
were intended for Mr. Burbank's own eye, to supplement
the records oj memory. When thousands of experiments
are being performed simultaneously, it is im-
perative that the recording should be done
with the least possible loss of time.

RECORDING THE EXPERIMENTS

convenience, as it will enable any particular lot
of plants to be located, even if through some inad-
vertence the label stakes, which are an absolute
necessity, have been removed or lost by careless
workmen.

Often when planting in the field, letters or
numbers are used on the stakes, corresponding
with similar letters or numbers in the record book.
LABEL STAKES AND LABELS

As to the label stakes themselves, the ones that
I habitually use for general field culture are about
20 inches long, 2 inches wide, and % of an inch in
thickness. They are smoothly planed and painted
about half way down on both sides with common
white lead paint.

One coat of paint is far better than two, for
if a pencil is used the lightly painted surface
takes the lead to advantage, and by bearing down
heavily with the pencil, indentations are made in
the wood that will resist the weather more effec-
tually and thus give greater permanence to the
record.

It is desirable to make the label stakes of soft,
smooth redwood or other durable wood. In the
East the locust is an excellent substitute. It is
advantageous to dip the end of the stake in car-
bolic acid or in a solution of sulphate of copper
to prevent decay. These stakes may be used over

[261]

LUTHER BURBANK

and over again for many years, being planed off
as the occasion requires and repainted.

Many thousands of these label stakes are used
each season on my experimental grounds. For
smaller beds I use a stake usually 1 inch wide,
from % to % of an inch thick, and from 10 to 14
inches in length. These smaller plant stakes may
be purchased of dealers, and are prepared for use
in the same way as the larger ones.

For use on trees a special label is employed,
to make records of budding, grafting, and varia-
tion. This label is usually 5 or 6 inches long, and
from 3-16 to % of an inch thick. It is notched
at one end and attached to the branch of a tree
with a piece of pliable galvanized iron wire. The
wire should be loose enough to avoid any danger
of strangling the branch.

The labels are painted with white lead. They
sometimes remain upon the trees for five, ten or
even fifteen years. To inscribe these permanent
labels, I use a thick black paint, composed of a
mixture of lamp black, linseed oil, and a little
turpentine, applying the mixture with a small
camel's hair brush. The names of varieties, the
parentage, and other important matters are thus
recorded. Then, while the paint is still wet, some
fine dry sand is sifted over the label so as to
protect the paint from the weather.

[262]

Ripening Record

This may 6e regarded as a companion record to the

one shown on page 257. 7f records the highly important

matter of the time of ripening oj various fruits. This particular page

shows among other things that a seedling Japan raspberry ripened April

2$th, and a new hybrid blackberry May ist. Some of Mr. Burbank's

finest new fruits, including the Burbank cherry and the Sugar prune

are made doubly valuable by the fact that they ripen several weeks

earlier than similar fruits of other varieties. Mr. Burbank

is constantly encouraging fruits, by selective breeding,

to modify or lengthen their season of fruiting.

LUTHER BURBANK

In addition to the labels and stakes I have just
described, a small cardboard label of light weight
is needed for making record of the hybridizing
experiments. The common cardboard shipping
tag about 1% inches by 3 inches in size with a
reinforced eyelet hole, is generally used on plants
with tender stems; and where the wind is likely
to disturb larger labels, half or two-thirds of the
cardboard may be cut off, leaving barely space to
inscribe the record.

Where these tags are used in extensive pollena-
tions of many varieties on a single tree, it is not
always necessary to write the record, for the same
object may be accomplished by cutting off one
corner of the card to indicate a certain variety of
pollen, and a second corner to indicate another
variety; additional varieties being represented
by series of notches. Or the same end may be
attained by punching holes in the card with a
pocket steel punch. This plan saves much time,
and the record is more permanent than if it were
made with pencil. A large number of tags may
be prepared at once with punch or scissors.

Tags of this character are less likely to have
their records erased by wasps and hornets, which
often partially destroy labels when securing mate-
rial for their paper homes.

Conspicuous tags such as these are $lso of aid

[264]

RECORDING THE EXPERIMENTS

later in the season when the seed is to be gathered;
because they make known at a glance the facts as
to parentage, and make it possible to keep sepa-
rate the seeds of different varieties. The labels
are tied to the plants with common twine, as wire
or other hard substances would be likely to injure
the tender stems when the wind moves the tags
about.

When numerous varieties of plants are grown
in a single bed, we often nail a common tree label
opposite each row on the board that borders the
bed, instead of using a stake, as there is less danger
of the label being displaced. It will be advan-
tageous to place this label at the side of the bed
away from that from which the prevailing winds
and storms come. In this section of California
the summer winds and winter storms come from
the South, East, and Southwest, and in conjunction
with the hot sunshine, they are very destructive
to paint. So it is advantageous to face the labels
toward the North.

All of these are matters of minor detail, yet not
without their importance.

RECORDING RESULTS

In making selection of individual plants that
are to be preserved, or from which seed is to be
gathered, the most convenient, and at the same
time the most accurate method is the simple one

[265]

Budding Records

It has sometimes been supposed that Mr. Burbank
depends entirely on his memory ; and makes very Jew written
records oj his experiments. This facsimile page, taken in connection
with the others that have just been shown, will serve to dispel that
erroneous notion. It will be seen that records are kept of the essentials
of each different type of experiment, including not only methods,
but results. In point oj Jact, although Mr. Burbank adopts
many shortcuts, his records oj essentials are surpris-
ingly comprehensive and complete, considering
the enormous range oj his experiments.

RECORDING THE EXPERIMENTS

of tying a small strip of cloth about the stem of
the plant.

Visitors to my gardens are sure to notice that
each bed of flowers has a half dozen or so plants
that are thus decorated. In some cases two or
three strings may be attached to a single plant,
indicating degrees of excellence. Selection having
been made in this way, the plants may be allowed
to ripen their seeds, and in due course the work-
men may gather them without further direction,
placing them in labeled boxes to be stored for the
winter.

As regards new fruits, there is particular need
of great accuracy, and here it is impossible to
avoid a good deal of detail. It will not do at all,
in dealing with a valuable addition to the list of
fruits, to leave anything to memory as to its season
of ripening, size and form, color, flavor, aroma,
size of core or stone, length of stem, or any other
essential quality.

An exact record must be kept of these items,
and for this purpose a book with removable
unruled leaves is the most satisfactory.

The fruit should be cut in half with a sharp
knife. The incised surface may then be placed
directly on the paper, and the outline of the fruit
traced with pencil. The specimen may similarly
be outlined in cross-section. This preserves a

[267]

"S»«~i

RECORDING THE EXPERIMENTS

graphic record of the exact size and form of the
fruit. The main character of the inside of each
fruit may be indicated, and by adding the date
of ripening, the time of its earliest and medium
ripening, the number of days it will remain in
good condition upon the tree, its keeping quality
when packed for shipment, and its susceptibility
to the ravages of insect pests and fungoid disease,
we have on a single sheet a fairly complete and
very valuable record, together with a graphic rep-
resentative of the size and form of the fruit itself.

Record will be made in the same way in suc-
cessive seasons of fruit from the same tree, with
additional record of the appearance of any new
characters or qualities. Comparison of the rec-
ords will show whether the fruit on the young
trees has increased in size, improved in quality,
or varied in time of ripening from year to year.
Not unfrequently the record of the third year
shows a very considerable increase of good
qualities over the first.

After a record has been kept for four or five
seasons, a fair estimate may be made of the gen-
eral value of this particular fruit. If in addition
we know the characteristics of the parent forms —
whether the ancestors were hardy or tender, and
the like — we are now in position to form a clear
judgment as to the probable value of the fruit.

[269]

Punched Labels

These labels are important time-savers. Each set of
holes represents a specific plant or a different type oj experi-
ment, the key to the labels being found in the record books. The upper
left hand label here shown might indicate, for example, that the branch
on which it is tied bears blossoms of the Sugar prune (one hole at base
of label), fertilized by pollen of the Conquest stoneless prune
(three holes at center of label). Such labels as this are
loosely attached to the stem of the plant that has
been pollenized or grafted. They are per-
manent, and they minimize mistakes.

RECORDING THE EXPERIMENTS

Such a record as this is essential to actual
progress. It is important, if for no other reason,
to prevent the experimenter from deceiving him-
self. It is very easy to imagine that a certain
product that has caused one much trouble is better
than some other; or that a fruit of a given tree is
larger than some rival variety. But the record
book enables one to put the matter to a precise
and definite test; it makes self-deception impos-
sible; and it affords an invaluable guide to further
experimentation.

There are thousands of graphic records such
as these on the shelves of my library.

I would not think of attempting to conduct
an intricate series of experiments looking to the
development of a new fruit without the aid of
these plan books.

When the experiment is finally completed, a
series of these loose leaves, properly collated,
furnishes a complete record of the various hybrid-
izings and selections — resulting sometimes in
better and sometimes in worse fruits — through
which success has finally been achieved. These
records are in themselves sufficient answer to any
one who imagines that the plant experimenter
works haphazard, merely because he does not
always adopt a biometric method.

After all, from the standpoint of the consumer

[271]

Notched Labels

This is another type oj short-hand label similar in
its use and interpretation to the ones shown on page 270.
Each series oj notches tells a different story, and the key to their inter-
pretation is found in the record books. Two notchest /or example,
might represent the Alaska daisy and three notches the variety named
Westralia. The top label above would then record the hybridizing
oj these two varieties. (The small notches for the
string are not counted.) Mr. Burbank finds this
method oj keeping track oj experi-
ments highly satisfactory.

RECORDING THE EXPERIMENTS

who makes up the main bulk of the population,
and whose tastes and needs are the criterion by
which the plant experimenter's results will be
judged, it is the final product rather than the
precise method by which it is attained that is
important. But the ideal at which the plant
experimenter aims would probably never have
been realized had he not given himself the aid of
some such system of quick and accurate records
as my plan books present.

—Once the principles of hybridiza-
tion and selection have been clearly
mastered, they may be applied to
almost every variety of plant life.
There are differences in detail, but the
broad outline is the same for each.

Variation in Corn SeeJ

Af r. Burfcanfe Jinds material for most of his experi-
ments in variations as to one quality or another that appear
among plants oj the same species. It may or may not be necessary to
accentuate variation by hybridizing experiments. The range oj
^ariation that may be shown in the seed oj a single species
is illustrated in this lot of kernels oj corn, which show
surprising diversity in shape, size, and color.
Numberless new varieties could be devel-
oped through selective breeding from
such a lot oj seed as this.

FINAL SELECTION

THE MOST IMPORTANT TASK OF ALL

IN FARMING districts of the Mississippi Valley
they have a curious custom in selling cattle at
auction. They drive a herd of cows together
and the auctioneer asks his audience to bid for
first choice, no individual animal being specified.

The highest bidder makes his choice, and the
cow he selects is taken from the herd.

Then the auctioneer starts over, receiving bids
for "first choice" among the remaining animals.
This process is repeated again and again until all
the exceptional animals have been selected.

A curious result of the method is that it very
commonly happens that different bidders have
their eyes on different animals. Farmer A, who
bid highest at the outset, did not have in mind the
animal for which farmer B was bidding. And so
it often happens that after six or eight selections
have been made a cow still remains that was

[VOLUME III — CHAPTER IX]

LUTHER BURBANK

regarded by some of the bidders as the very best
one of the entire herd.

A man who bid unsuccessfully again and again
may thus, in some cases, finally have his choice
precisely as if he had made the highest bid at the
outset.

The obvious explanation both of the method
and of its somewhat anomalous results is found in
the fact that individuals differ in their judgment
as to what constitute the superior qualities of a
cow. Each bidder has noted an animal that
particularly appeals to him, and each is backing
his own judgment in making selection. The result
is a process of elimination that may or may not
select from the herd the best animals at the very
outset.

"But what have cows and their selection to do
with the development of new varieties of plants?"
you ask.

Nothing direct and obvious to be sure. But it
has often occurred to me that the process of selec-
tion at the Iowa auctions is closely comparable to
that which is employed by the plant experimenter
in the course of his every-day work. In lieu of a
herd of cattle, he deals with a group of seedlings.
But his task is precisely like that of the auction
bidder in that he must select from among scores
of plants of the same kind, and often of closely

[276]

Chilian Beans

This lot oj beans affords another striking instance of
the wide range of variation among the seeds of individual
plants of the same species. It may be assumed 'that these widely diver-
gent seeds represent various heredities. Each plant is, in point
of fact, a mosaic of characteristics inherited from many lines
of ancestry. In Mr. Burbank's phrase, heredity is
the sum of past environments. A curious and
important feature of the matter is that the
different racial strains may be segregated,
as illustrated in this lot of beans.

LUTHER BURBANK

similar appearance, the one that seems to him the
choice of the entire lot; and then in succession the
second and third and fourth best, until he has
chosen possibly six or eight individuals out of a
group of hundreds or thousands.

These six or eight individuals will be preserved
for use in further experiments. They are the ones
with which the attempt to improve the variety to
which they belong will be carried out.

And the ultimate success of the entire experi-
ment in plant breeding will very largely be deter-
mined by the perspicacity with which the selection
of these few individuals was made. Nor can we
doubt that it must often happen, in the case of the
seedlings as in that of the cattle, that after the final
selection has been made there remain, unknown
to the experimenter and in contravention of his
judgment, better plants among those rejected than
any one that he has chosen.

It could not be otherwise when we consider
the large numbers involved, the variety of plant
characteristics, and the great diversity of traits
represented in a single generation of hybridized
seedlings. Yet, on the other hand, experience
should enable the experimenter to choose with a
relative degree of certainty, and it is possible to
acquire a degree of skill, based on careful obser-
vation of the minute details of plant structure,

[278]

FINAL SELECTION

that will give full assurance of a capacity to select
with at least a large measure of success.
A HALF HOUR IN THE ORCHARD

It is usually a surprise to any visitor who comes
to my orchard at a time when I am making selec-
tions among seedlings of many kinds to observe
my method.

Many people have expressed astonishment
when they have seen me wralk rapidly along a row
of plum trees saying: "Kill this one, and that one,
and that; save this one, and that one yonder";
indicating the choice between plants to be saved
and those to be destroyed so rapidly that the men
following me can scarcely tie strings to the selected
ones as fast as they are chosen.

In this way I may test from five to ten thousand
young trees as I walk along the row, scarcely
pausing for more than what seems the most casual
glance. But my eye takes in the important thing.
I know just what I am looking for. And if my
judgment in the matter had not proved in the main
good, the output from my orchard would have
been quite different from what it has been.

I may recall by way of illustration an experi-
ence in which my selective judgment was put to a
practical test — no different a test, to be sure, from
thousands that I myself have made, but having
added interest because it was made by another.

[279]

LUTHER BURBANK

It chanced that a well known judge, who is
also a horticultural enthusiast, who had been very
much interested in my work, was visiting me at
a time when I was sorting out plum trees from
among a lot of several thousand seedlings about
a foot high. I had a man carrying them away as
fast as selected. They were thrown in three piles,
the first containing those I had declared to be the
best ones for continuing the test; the second pile
containing those I thought possibly worth trying;
and the third pile those that seemed to me no good
at all.

The judge watched me for a few minutes and
then said: "You are picking them altogether too
fast. You cannot possibly tell like that which are
good and which are not."

I replied : "Wait and see, or test the matter for
yourself if you wish."

"Very well," said my visitor, "I will do so."

And therewith he selected a few seedlings from
each of the piles and took them home with him to
graft on trees of his own.

Of course it was necessary to wait two or three
years for results. But when the time came, the
judge very cheerfully admitted that I had been
quite right all along the line. The cions from
my discarded pile bore fruit that was almost
worthless; those from the intermediate pile gave

[280]

1-gif*!

LUTHER BURBANK

fairly good fruit; and from the pile of my first
choice seedlings he secured a fruit of such quality
that he named it the Klondike, declaring that it
gave him more good plums than he had ever had
before from a similar tree.

I cite the incident as showing the possibility
of gauging fruiting qualities of a seedling at a time
when the plant itself is a mere sapling a few inches
in height. The capacity to make such selection
has sometimes been spoken of as intuition; but
it is really a matter of observation and practice.
One learns through long experience to judge what
characteristics of the seedlings are suggestive of
possibilities of fruit-bearing.

And after all this is no more than judging the
man of the future by observation of the child of
to-day.

THE CORRELATION OF PARTS

If we were to state the matter a little more
technically we might say that such selective judg-
ment as I have just illustrated is based on a
knowledge of the correlation between the different
parts or members of a plant's organization.

It was first prominently brought out, I believe,
by the French naturalist Cuvier something over
a hundred years ago that there is always a
correlation between the different structures of a
given animal, to accord with its habits of life.

[282]

FINAL SELECTION

For instance the teeth and claws of a cat are
associated with its carnivorous habits and are
linked with a certain structure of legs and muscles
adapting the creature to spring forward with great
celerity upon its prey.

A somewhat different structure of body and
limb is associated with the talonless feet of the
dog tribe which are adapted to rapid running for
prolonged periods rather than to sudden leaping
and clutching.

It was by careful study of the correlation of
parts, of which these are only crude and familiar
examples, that Cuvier was enabled to gain an
insight into the characteristics of fossil animals
of which only small fragments of skeletons
were preserved in the rocks. The science of
comparative anatomy was the outgrowth of his
observations.

Now it is at once obvious to anyone who studies
plants attentively that their structure also shows
a corresponding and no less invariable correlation
of parts. The more conspicuous illustrations of
this are obvious to the most casual observer —
various adaptations of form of tree and shrub and
vine to their natural surroundings are so patent
that they cannot escape attention.

But of course the plant experimenter must deal
with correlations of a very delicate order. He

[283]

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FINAL SELECTION

is called upon to make nice distinctions between
individual seedlings of the same variety. All will
have the same general formation of stem and leaf.
He must look, then, for details of variation
that would altogether escape the notice of the
untrained observer. But that such differences
exist, and that they are signs that to the practiced
eye are of the utmost importance, any successful
plant experimenter can testify.

It would obviously be futile to attempt a
detailed description of the nice shades of
distinction between various seedlings of the same
race upon which the plant experimenter depends
in forming his selective judgments. That, clearly,
must be matter for practical observation. It can
be learned nowhere but in the field. But perhaps
two or three illustrations may be given that will
at least serve in a general way to suggest what
manner of traits are taken into consideration
when the plant experimenter is choosing the
individuals with which he is to continue his
experiment.

A FEW PRACTICAL HINTS

In selecting raspberry or blackberry plants for
color of fruit, for example, there is almost always
a correlation of the plant and fruit that will
foretell the future crop.

I have observed in thousands of instances that

[285]

LUTHER BURBANK

vines that have purple spines and canes will in
future produce berries that are dark purple or
dark red in color. Pinkish leaves, on the other
hand, foretell fruit of light pink or red color;
plants with yellowish vines and foliage may be
expected to produce berries of a yellowish color.
Very pale foliage and canes usually indicate that
the crop will be of a whitish or amber color.

A knowledge of this correlation between vine
and fruit was of great service to me in my later
experiments for the development of the race of
white blackberries. It enabled me to select for
transplantation and particular care vines that
would produce the type of berry I was seeking.
It was not necessary to await the time of fruiting
in order to gauge progress.

The correlation of characters between the vine
and the fruit of the grape is not always quite
so clearly established, yet it is often observable.
Grape tentacles may give clear indication of the
size and flavor of the future bunches of fruit.
Long before a grape vine has come to the age
of fruiting, the taste of the tendrils may give
a fair idea of the flavor of the grapes it will
ultimately bear.

Moreover the seedling vines that produce bushy
stems that are small and much branched, and
have small leaves, will almost invariably produce

[286]

FINAL SELECTION

meager clusters of small fruit of poor quality. So
the wise experimenter will root out such vines
without letting them come to maturity.

Among plums and peaches the correlation of
characters is exceedingly valuable.

The case of the plum seedlings already cited
suggests the possibility of p re-judgment of fruit
from observation of small seedlings. There are
a good many characters of leaf and twig that are
almost too intangible for description, like the
changing expressions of the human face, or like
delicately graded colors, yet which to the practiced
eye are full of meaning.

COLOR OF FOLIAGE A GUIDE

A broad general distinction that is fairly
obvious to any observer is found in the color of
the foliage. It may be expected that a plum or
peach seedling having foliage of a reddish purple
color will produce fruit dark-colored not only in
skin but in flesh. And of course the selection
made from any given lot of seedlings will depend
largely upon the particular qualities that one
desires to develop.

But, as repeatedly pointed out, in practical
work one is usually looking for a combination of
qualities; and, by the same token, one usually
inspects his seedlings for the combination of
characteristics of stem and leaf and color. He

[287]

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FINAL SELECTION

seldom has his choice determined by a single
characteristic, obvious or otherwise.

SELECTING FOR A SINGLE CHARACTER

Yet there are cases where an experimenter is
working with a single plant-characteristic in view,
as, for example, when I successfully attempted to
develop scented callas and dahlias and verbenas.

Here, obviously, the task of selection is com-
paratively simple. We are dealing in each case
with a flower that has certain desired qualities of
color that are firmly fixed in its heredity. The one
conspicuous point of variation among thousands
of specimens is the presence or absence of a
pleasing aroma.

It is necessary, then, merely to select the
individual plants that have the most pleasing
perfume and to use these only for carrying on the
experiment. By making such selection generation
after generation, choosing always the sweet-
scented and rejecting the others, it proves possible
to accentuate and fix the quality of perfume-pro-
duction without altering the other characteristics
of the respective flowers in question.

Again the quality sought may be a particular
color of blossom, and it may be desirable to pay
attention to this only, practically disregarding
all other qualities. Such, for example, was the
case with my experiments with the crimson

[289]

LUTHER BURBANK

Eschscholtzia, commonly known as the California
poppy.

The blossoms of the plant from which my
new type of poppy was developed, had a narrow
strip of crimson on the inner side of one petal.

This was an anomaly that appeared "spon-
taneously." Doubtless it was due to some crossing
of ancestral strains that brought out a latent
character that had long been suppressed. But as
to this we can only surmise. The simple fact
of the matter was that a blossom did appear that
had this narrow strip of crimson on one petal.
I seized on this individual blossom as offering
material for an experiment in color variation.

Seeds from this plant produced the next year
several plants that had a trifle more crimson on
their blossoms.

The following year there was still further
improvement, as plants appeared that showed
a much larger invasion of the flower petals
by the crimson coloring. And by selecting year
after year blossoms that showed this increasing
tendency to adopt the new color, I produced
presently a plant that bore blossoms of a beautiful
uniform clear crimson. No trace of the original
color remained.

This furnishes a very good illustration of
selection for color where the material consisted

[290]

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LUTHER BURBANK

of a small strip of an unusual color appearing on
blossoms otherwise of a fixed hue.

But the same method of selection may some-
times be applied to the improvement of the shade
of color, or even to the development of a new color,
from a flower that shows only a faint departure
in shade from the normal. And the same principle
of selection, followed out in precisely the same
manner, applies to the development of flowers or
fruits of varying size, of larger or smaller stem,
abundance of blossom, profusion of leaf or flower
or fruit, and the like.

It is equally possible to alter the proportions
of the chemical constituents of a plant in certain
instances.

The case of my sugar prunes, which were
developed to have a sugar content of more than
23 per cent, as against the 15 per cent, of their
ancestral type, will be recalled. In a similar
way the sugar beet has by mere selection been
developed until the races now cultivated contain
several times the proportion of sugar of the
ancestral beets even of twenty years ago.

An interesting experiment in causing the
progeny of a certain plant to vary in opposite
directions through selection, has been made at
the Illinois Agricultural Station. Here the quality
under consideration was the protein content — that

[292]

FINAL SELECTION

is to say the amount of nitrogeneous matter— in
the kernels of a given variety of corn.

The specimen with which the experiment
started showed on analysis 10.92 per cent, of
protein. Selection was made, among the ears of
corn grown from this seed, of the individual
specimens having the highest protein content on
one hand, and those having the lowest protein
content on the other.

By continuing this double selection for ten
generations, two races of corn were developed,
one of which produced seed having an average
protein content of 14.26 per cent., while the other,
grown in the same field, showed a decrease to
8.64 per cent.

This experiment illustrates the possibility of
selecting out and fixing new races varying widely
as to a single important quality of grain among
the descendants of a parent plant of relatively
fixed strain. In point of fact no plant is so fixed
that its individual members do not show variation ;
none so fixed that it does not supply material with
which the experimenter may work in producing
new varieties.

Another illustration of the same thing was
given by an allied series of experiments at the
Illinois Station at which selection was made with
reference, to the height of the ear on the corn

[293]

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FINAL SELECTION

stalk. Seed from the same cob was planted in two
fields and grown always under closely similar
conditions.

But in one field selection was made for
breeding purposes from stalks having the ears
higher from the ground than the average; and in
the other field from ears that were lower than the
average. At the end of five years the two fields
were so widely diversified that the average height
of the ear from the ground in one of them was
less than three feet (33.2 inches), whereas in the
other field the average height of the ears was fully
six feet (72.4 inches).

One could not well ask a more striking
illustration than this of the possibility of devel-
oping new races, differing as to some conspicuous
character, by simple selection from a given stock.

The case of my winter rhubarb, which came
to have a relatively gigantic stalk, will be recalled
as of similar import; although in that case the
experiment was complicated by having to bear
in mind various other qualities in addition to mere
size of stalk. My giant corn and the corn with
the rainbow-striped leaves are other examples.
SOME ALARMING FIGURES

But, as repeatedly pointed out, the experiment
usually is complicated by the necessity for
considering more qualities than one whenever

[295]

LUTHER BURBANK

selection is made with an eye to the production of
a commercially valuable variety of flower or fruit
or vegetable, and not merely for the purpose of
scientific record.

We have seen this illustrated again and
again; and we have seen also how great are the
complications which result when we are called
upon to make a selection that will give us not
merely one quality — merely size or a given color
or sugar content — but a combination of six or
eight or ten qualities, all presented in superlative
measure.

We have seen that the chance of securing any
given combination of qualities decreases at a
startling geometrical ratio in proportion as the
number of qualities increase.

The precise formula, as calculated by the
biometricians, runs something like this. In case
a single pair of qualities is in question — say high
protein content versus low protein content in
corn — the chances are, if the two strains are
crossed, that there will appear in the second
generation of their progeny one offspring in four
that closely resembles each parent.

But when we are considering two qualities-
say protein content and height of ear on the
stalk— in combination, the chance that there will
be an individual of the offspring like each parent

[296]

FINAL SELECTION

in the progeny of the second generation, is only
one in 16.

And when three qualities are in question the
ratio jumps to one in 64; with four qualities it
advances to one in 256; with five qualities, to one
in 1026. When eight qualities are in question,
the chance of producing one offspring showing
precisely the combination of qualities of each
parent is only one in 98,496.

And when we deal with ten qualities we
encounter the altogether disconcerting ratio of
one to 1,575,936!

All of which makes it very clear that the wise
plant experimenter does not depend upon mere
chance to give him the combination of desired
qualities in the production of a new form of flower
or fruit. He must make his selection, in any
given generation, with reference to one or two
pre-eminently desirable qualities, and must be
content to accept for the moment such other
qualities, however undesirable, as are associated
with the desired ones.

MULTIPLE SELECTION

For example, in developing a stoneless plum,
my earliest selections were made with an eye to
stonelessness alone.

Then as I gradually developed a race of plums
in which I was certain of finding a fairly large

[297]

Inferior Plum Seedling

This seedling should be compared with the ones shown

on pages 300 and 302. It will be seen that the one here shown

is only about ten inches high, and that it branches irregularly, and has

a curved stalk, forecasting a tree oj small size and poor

formation. The leaves also are small in

size and oj inferior quality.

FINAL SELECTION

proportion of individuals growing stoneless fruit,
I could select among these the ones that combined
with stonelessness the largest proportion of other
good qualities, such as size and color and flavor
and abundant bearing.

When presently I had, through selection,
developed a somewhat fixed strain that combined
the qualities of stonelessness with fair size and
good flavor, I could then select among the many
individuals showing these qualities the particular
ones that showed them in fullest measure; and
at the same time I could now have in mind one
or two other qualities — say color of fruit and
keeping quality — and be guided in my selection
by a consideration of these traits in addition to
the others that had already been fairly fixed.

Thus the matter of selection, even when many
qualities are to be combined in the ultimate
product, is not quite so hopelessly complex as the
calculations of the biometricians might lead one
to suppose. Yet it is assuredly complex enough
to test the patience and the ingenuity of the
experimenter to the last degree.

So the amateur who enters this fascinating
field will do well to begin with simple cases,
paying heed to a single quality of any flower or
fruit with which he experiments; endeavoring to
advance along one line till he acquires skill

[299]

Fairly Good Plum Seedlings

These seedlings are intermediate in quality between

the one shown on page 298 and that on page 302. They are

about eighteen inches tall, and the better one is of upright growth with

large well-Jormed leaves. But it has a rather scant

equipment of branches.

FINAL SELECTION

enough through practice to attempt more complex
experiments.

Let him, for example, increase the perfume of
some familiar garden plant, or develop a race
having large blossoms, or one having peculiar
brilliancy of color.

Any flower bed will show him, among different
specimens of the same species, enough of variation
to furnish material for his first selection. And
he is almost sure to find encouragement through
discovery, among the plants grown from this seed,
of some that will show the particular quality he
has in mind in a more pronounced degree than
did the parent plant.

So here he will have material for further
selection, and step by step he can progress in
successive seasons, often more rapidly than he
had dared to hope, toward the production of the
new variety at which he aims.

Of course the time will presently come when
the amateur who thus begins with what may be
called the alphabet of plant experimentation, will
wish to advance to more complicated projects. He
will wish to urge his plants along a little more
rapidly on the path of variation by means of
hybridization.

But even here, as will be obvious on a moment's
reflection, the experimenter is still dealing with

[301]

Perfect Plum Seedling

This seedling contrasts markedly with the one on

page 298 and considerably with those on page 300. It is

nearly two feet tall; its stalk is relatively thick, and absolutely perpcn-

dicular; it has a fine spread of symmetrically arranged branches; and

its leaves (shown in smaller scale than the others because of the larger

size of the tree) are oj perfect shape and of fine color and texture. This

seedling may be depended on to make a tree far superior to

those shown in the other illustrations. Mr. Burbank

confidently selects this seedling as the

future bearer of valuable fruit.

FINAL SELECTION

selection. For of course he will not make his
hybridizing tests at random, but will select for
his parent stock individuals that manifest in
pronounced degree the qualities that he wishes
to combine in his projected new race.

So when we pass from the stage of simple
selection of "spontaneous" variations, to the
stage of inducing variations along given lines by
cross-breeding, we are not abandoning selection
but are only dealing with selection in its more
complicated aspects.

Rightly understood, then, it is not too much
to say that the entire task of the plant developer
is a matter of selection. First, he may select
varieties as nature presents them to him. Second,
he may through selective breeding improve these
varieties. Next he selects among these and makes
combinations for further variations; and then he
is ready for a new series of selections. So from
first to last it is only the same story presented in
different aspects.

How important a part does selection play in
the life about us! Whether it be in animal or
human life, whether it be the selection of materials
for a nest, an appropriate club or stone to lay low
an enemy, the selection of materials for a dynamo
or a pyramid, or of words to convey certain
thoughts, aspirations or emotions; but selection

[303]

LUTHER BURBANK

alone from among all the materials supplied by
nature no matter how skillfully carried out can
never produce the artist's ideal in pigments or
marble, the architect's vision of a great struc-
ture for the shelter of thousands — universal
standards of excellence — unless their production
is accomplished by means other than metrical
and statistical!

The beginning is selection and the end is
selection.

[END OF VOLUME III]

LIST OF

DIRECT COLOR PHOTOGRAPH PRINTS
IN VOLUME III

Apple p.,*

Two Burbank Apples 196

Artichoke

Giant Artichoke in Blossom , 89

Balloon Berry

Balloon Berry Blossom 79

Balloon Berry Bush After Pollenation 81

Bean

New Chilian Beans 243

(See also reierence under "Variation.")

Budding

Cutting a Bud 181

Cutting the Bark to Receive a Bud 182

The Bud Graft Completed 183

Bud After a Year's Growth 185

Bud With Stock Cut Away 187

Cactus

Cross-Section of a Cactus Blossom. 65

Mr. Burbank Selecting Cactus Seedlings 284

Chestnut

Pollen-Bearing Chestnut Blossom 92

Stigmatic Chestnut Blossoms 93

Corn

Hybrid Corn 33

Ten Corn Variations 37

Corn Tassels Bearing Kernels 41

Corn Tassel Growing From the Ear 45

Corn Seventeen Feet High 49

Corn Self-PoIIenated and Crossed With Teosinte 95

Corn Insufficiently PoIIenated 97

Selected Ears of Corn Drying 101

Selected Corn Seed 105

Protecting Test Corn from the Breezes 142

(See also reference under "Variation.")

LIST OF ILLUSTRATIONS (Continued)

Dandelion p.ge

Wild and Improved Dandelions 203

Germination

Germinating Seeds in Damp Cloth 106

Seeds Germinated in Damp Cloth 107

Pumpkin Seeds Germinated in Wet Newspaper 109

The Burbank "Flats" 113

" Flat" With Layer of Gravel . . ,. 115

"Flat" Partly Filled with Dirt 117

" Flat" After Seeds Are Sown 119

Gourd

Two Gourd Blossoms to be PoIIenated 68

PoIIenating the Gourd Blossoms 69

Grafting

Cleft Graft Frontispiece

Complete Grafting Outfit 144

Cutting Cion for Whip Graft 149

Cutting Stock for Whip Graft 151

Whip Graft in Place 153

Whip Graft Waxed 155

Whip Graft Bandaged 157

Grafted Wood 161

Cutting Stock for Cleft Graft 163

Cleft Grafts Waxed and Unwaxed 165

Side Graft in Position 167

Side Graft on a Root 169

The Root Graft Completed 171

Crown or Bark Graft 173

Bridge Graft 175

Cutting Stock for Top Graft 177

Top Grafts in Place 179

Quince Cion Ready for Grafting 189

Cions Showing One, Two, and Three Buds 193

(See also "Budding.")

Grape

Pollen-Bearing Grape 86

Wild Grapes 234

Seedless Grapes 239

Hybridization

A Mosaic Leaf 53

LIST OF ILLUSTRATIONS (Continued)

Labels and Records Page

Labels on Tree Graft 248

Label on Greenhouse "Flat" : 251

Diagram of Tree Grafts 254

Record of Blooming 257

Grafting Record 260

Ripening Record 263

Budding Records . . . 266

Stakes to Mark Divisions of a Verbena Bed 268

Punched Labels 270

Notched Labels 272

Marigold

Common, French, and Burbank Marigolds 30

Peach

Wild Flowering Peach, and Improved Variety 21

Two Burbank Peaches. . 2ii

Pear

A Japanese Pear 19

The Chinese Pear 23

Pears with Blended Heredities 27

Pear Seedlings 281

Plum

Inferior Plum Seedling 298

Fairly Good Plum Seedling 300

Perfect Plum Seedling 302

PoIIenizing

Complete Kit of PoIIenizing Tools 83

(See also pictures listed under "Balloon Berry,"
"Cactus," "Chestnut," "Gourd," "Pumpkin," etc.)

Poppy

A Shirley Poppy — Showing Reproductive Organs 56

The Stigma of a Poppy, Greatly Enlarged 59

Pumpkin

Pollen-Bearing Pumpkin Blossom 62

Seed-Bearing Pumpkin Blossom 63

Rose

Rose Cuttings 229

LIST OF ILLUSTRATIONS (Continued)

Seedlings P^

"Flats" with Sprouting Seedlings i 121

Seedlings in the Greenhouse 123

Protecting Seedlings from the Birds 125

Mr. Burbank's Only Cold Frame 127

Mr. Burbank's Cloth Screens 129

(See also references under "Pear" and "Plum.")

Squash

Patagonian Squash 220

Strawberry

A Burbank Strawberry. 6

Strawberries Showing Variation. 1 1

A Giant Strawberry 15

Strawberry Blossom Ready for PoIIenating 73

Strawberry Plant After PoIIenation 75

Strawberry Bed Before Selection 288

A Standard Strawberry 291

Strawberry Bed After Selection 294

Transplanting

Setting Out Plants from the "Flat" 131

Making a Trench for Cuttings 133

Setting Out Cuttings in the Trench. 135

Tamping the Dirt Around the Cuttings 137

Seedling Trees Awaiting Transplantation 139

Variation

Variation in Corn Seed 274

Chilian Beans 277

Verbena

Verbena Bed 209

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