Terminology is an awkward thing. It is as disagreeable to be compelled
to make new names, as to be constrained to use the old faulty ones.
Different readers may associate different ideas with the same terms, and
unfortunately this is the case with much of the terminology of the
science of heredity and variability. What are species and what are
varieties? How many different conceptions are conveyed by the terms
constancy and variability? We are compelled to use them, but we are not
at all sure that we are rightly understood when we do so.
Gradually new terms arise and make their way. They have a more limited
applicability than the old ones, and are more narrowly circumscribed.
They are not to supplant the older terms, but permit their use in a more
general way.
[310] One of these doubtful terms is the word _sport_. It often means
bud-variation, while in other cases it conveys the same idea as the old
botanical term of mutation. But then all sorts of seemingly sudden
variations are occasionally designated by the same term by one writer or
another, and even accidental anomalies, such as teratological ascidia,
are often said to arise by sports.
If we compare all these different conceptions, we will find that their
most general feature is the suddenness and the rarity of the phenomenon.
They convey the idea of something unexpected, something not always or
not regularly occurring. But even this demarcation is not universal, and
there are processes that are regularly repeated and nevertheless are
called sports. These at least should be designated by another name.
In order to avoid confusion as far as possible, with the least change in
existing terminology, I shall use the term "ever-sporting varieties" for
such forms as are regularly propagated by seed, and of pure and not
hybrid origin, but which sport in nearly every generation. The term is a
new one, but the facts are for the most part new, and require to be
considered in a new light. Its meaning will become clearer at once when
the illustrations afforded by [311] striped flowers are introduced. In
the following discussion it will be found most convenient to give a
summary of what is known concerning them, and follow this by a
consideration of the detailed evidence obtained experimentally, which
supports the usage cited.
The striped variety of the larkspur of our gardens is known to produce
monochromatic flowers, in addition to striped ones. They may be borne by
the same racemes, or on different branches, or some seedlings from the
same parent-plant may bear monochromatic flowers while others may be
striped. Such deviations are usually called sports. But they occur
yearly and regularly and may be observed invariably when the cultures
are large enough. Such a variety I shall call "ever-sporting."
The striped larkspur is one of the oldest garden varieties. It has kept
its capacity of sporting through centuries, and therefore may in some
sense be said to be quite stable. Its changes are limited to a rather
narrow circle, and this circle is as constant as the peculiarities of
any other constant species or variety. But within this circle it is
always changing from small stripes to broad streaks, and from them to
pure colors. Here the variability is a thing of absolute constancy,
while the constancy consists in eternal changes. Such apparent [312]
contradictions are unavoidable, when we apply the old term to such
unusual though not at all new cases. Combining the stability and the
qualities of sports in one word, we may evidently best express it by the
new term of eversporting variety.
We will now discuss the exact nature of such varieties, and of the laws
of heredity which govern them. But before doing so, I might point out,
that this new type is a very common one. It embraces most of the
so-called variable types in horticulture, and besides these a wide range
of anomalies.
Every ever-sporting variety has at least two different types, around and
between which it varies in numerous grades, but to which it is
absolutely limited. Variegated leaves fluctuate between green and white,
or green and yellow, and display these colors in nearly all possible
patterns. But there variability ends, and even the patterns are
ordinarily narrowly prescribed in the single varieties. Double flowers
afford a similar instance. On one side the single type, on the other the
nearly wholly double model are the extreme limits, between which the
variability is confined. So it is also with monstrosities. The race
consists of anomalous and normal individuals, and displays between them
all possible combinations of normal and monstrous [313] parts. But its
variability is restricted to this group. And large as the group may seem
on first inspection, it is in reality very narrow. Many monstrosities,
such as fasciated branches, pitchers, split leaves, peloric flowers, and
others constitute such ever-sporting varieties, repeating their
anomalies year by year and generation after generation, changing as much
as possible, but remaining absolutely true within their limits as long
as the variety exists.
It must be a very curious combination of the unit-characters which
causes such a state of continuous variability. The pure quality of the
species must be combined with the peculiarity of the variety in such a
way, that the one excludes the other, or modifies it to some extent,
although both never fully display themselves in the same part of the
same plant. A corolla cannot be at once monochromatic and striped, nor
can the same part of a stem be twisted and straight. But neighboring
organs may show the opposite attributes side by side.
In order to look closer into the real mechanism of this form of
variability, and of this constant tendency to occasional reversions, it
will be best to limit ourselves first to a single case, and to try to
gather all the evidence, which can be obtained by an examination of the
hereditary relations of its sundry constituents.
[314] This may best be done by determining the degree of inheritance for
the various constituents of the race during a series of years. It is
only necessary to apply the two precautions of excluding all
cross-fertilization, and of gathering the seeds of each individual
separately. We do not need to ascertain whether the variety as such is
permanent; this is already clear from the simple fact of its antiquity
in so many cases. We wish to learn what part each individual, or each
group of individuals with similar characters, play in the common line of
inheritance. In other words, we must build up a genealogical tree,
embracing several generations and a complete set of the single cases
occurring within the variety, in order to allow of its being considered
as a part of the genealogy of the whole. It should convey to us an idea
of the hereditary relations during the life-time of the variety.
It is manifest that the construction of such a genealogical tree
requires a number of separate experiments. These should be extended over
a series of years. Each should include a number of individuals large
enough to allow the determination of the proportion of the different
types among the offspring of a single plant. A species which is easily
fertilized by its own pollen, and which bears capsules with [315] large
quantities of seeds, obviously affords the best opportunities. As such,
I have chosen the common snapdragon of the gardens, _Antirrhinum majus_.
It has many striped varieties, some tall, others of middle height, or of
dwarfed stature. In some the ground-color of the flowers is yellow, in
others it is white, the yellow disappearing, with the exception of a
large mark in the throat. On these ground-colors the red pigment is seen
lying in streaks of pure carmine, with white intervals where the yellow
fails, but combined with yellow to make a fiery red, and with yellow
intervals when that color is present. This yellow color is quite
constant and does not vary in any marked degree, notwithstanding the
fact that it seems to make narrower and broader stripes, according to
the parts of the corolla left free by the red pigment. But it is easily
seen that this appearance is only a fallacious one.
The variety of snapdragon chosen was of medium height and with the
yellow ground-color, and is known by horticulturists as _A. majus luteum
rubro-striatum_. As the yellow tinge showed itself to be invariable; I
may limit my description to the red stripes.
Some flowers of this race are striped, others are not. On a hasty survey
there seem to be three types, pure yellow, pure red, and stripes [316]
with all their intermediate links of narrower and broader, fewer and
more numerous streaks. But on a close inspection one does not succeed in
finding pure yellow racemes. Little lines of red may be found on nearly
every flower. They are the extreme type on this side of the range of
variability. From them an almost endless range of patterns passes over
to the broadest stripes and even to whole sections of a pure red. But
then, between these and the wholly red flowers we observe a gap, which
may be narrower by the choice of numerous broad striped individuals, but
which is never wholly filled up. Hence we see that the red flowers are a
separate type within the striped variety.
This red type springs yearly from the striped form, and yearly reverts
to it. This is what in the usual descriptions of this snapdragon, is
called its sporting. The breadth of the streaks is considered to be an
ordinary case of variability, but the red flowers appear suddenly,
without the expected links. Therefore they are to be considered as
sports. Similarly the red forms may suddenly produce striped ones, and
this too is to be taken as a sport, according to the usual conception of
the word.
Such sports may occur in different ways. Either by seeds, or by buds, or
even within the single spikes. Both opposite reversions, [317] from
striped to red and from red to stripes, occur by seed, even by the
strictest exclusion of cross-fertilization. As far as my experiments go,
they are the rule, and parent-plants that do not give such reversions,
at least in some of their offspring, are very rare, if not wholly
wanting. Bud-variations and variations within the spike I have as yet
only observed on the striped individuals, and never on the red ones,
though I am confident that they might appear in larger series of
experiments. Both cases are more common on individuals with broad
stripes than on plants bearing only the narrower red lines, as might be
expected, but even on the almost purely yellow individuals they may be
seen from time to time. Bud-variations produce branches with spikes of
uniform red flowers. Every bud of the plant seems to have equal chances
to be transformed in this way. Some striped racemes bear a few red
flowers, which ordinarily are inserted on one side of the spike only. As
they often cover a sharply defined section of the raceme, this
circumstance has given rise to the term of sectional variability to
cover such cases. Sometimes the section is demarcated on the axis of the
flower-spike by a brownish or reddish color, sharply contrasting with
the green hue of the remaining parts. Sectional variation may be looked
at as a [318] special type of bud-variation, and from this point of view
we may simplify our inquiry and limit ourselves to the inheritance of
three types, the striped plants, the red plants and the red asexual
variants of the striped individuals. In each case the heredity should be
observed not only for one, but at least for two successive generations.
Leaving these introductory remarks I now come at once to the
genealogical tree, as it may be deduced from my experiments:
Year
1896 95% Striped 84% Red
| |
1895 Striped Individual Red Indiv.
\ /
1895 98% Striped 71% Red
| |
1894 Striped branches. Red branches.
\ /
1894 98% Striped 76% Red
| |
1893 90% Striped Indiv. 10% Red Indiv.
\ /
1892 Striped Individual
This experiment was begun in the year 1892 with one individual out of a
large lot of striped plants grown from seeds which I had purchased from
a firm in Erfurt. The capsules were gathered separately from this
individual and about 40 flowering plants were obtained from the seeds in
the following year. Most of them had neatly striped flowers, some
displayed broader stripes and spare flowers were seen with one [319]
half wholly red. Four individuals were found with only uniform red
flowers. These were isolated and artificially pollinated, and the same
was done with some of the best striped individuals. The seeds from every
parent were sown separately, so as to allow the determination of the
proportion of uniform red individuals in the progeny.
Neither group was constant in its offspring. But as might be expected,
the type of the parent plant prevailed in both groups, and more strongly
so in the instances with the striped, than with the red ones. Or, in
other words seed-reversions were more numerous among the already
reverted reds than among the striped type itself. I counted 2% reversion
in the latter case, but 24% from the red parents.
Among the striped plants from the striped parents, I found some that
produced bud variations. I succeeded in isolating these red flowering
branches in paper bags and in pollinating them with their own pollen,
and subjected the striped spikes of the same individuals to a similar
treatment. Three individuals gave a sufficient harvest from both types,
and these six lots of seeds were sown separately. The striped flowers
repeated their character in 98% of their offspring, the red twigs in
only 71%, the [320] remaining individuals sporting into the opposite
group.
In the following year I continued the experiment with the seeds of the
offspring of the red bud-variations. The striped individuals gave 95%,
but in the red ones only 84% of the progeny remained true to the parent
type.
From these figures it is manifest that the red and striped types differ
from one another not only in their visible attributes, but also in the
degree of their heredity. The striped individuals repeat their
peculiarity in 90-98% of their progeny, 2-10% sporting into the uniform
red color. On the other hand the red individuals are constant in 71-84%
of their offspring, while 16-29% go over to the striped type. Or,
briefly, both types are inherited to a high degree, but the striped type
is more strictly inherited than the red one.
Moreover the figures show that the degree of inheritance is not
contingent upon the question as to how the sport may have arisen.
Bud-sports show the same degree of inheritance as seed-sports. Sexual
and asexual variability therefore seem to be one and the same process in
this instance. But the deeper meaning of this and other special features
of our genealogical tree are still awaiting further investigation. It
seems that much important evidence might [321] come from an extension of
this line of work. Perhaps it might even throw some light on the
intimate nature of the bud-variations of ever-sporting varieties in
general. Sectional variations remain to be tested as to the degree of
inheritance exhibited, and the different occurrences as to the breadth
of the streaks require similar treatment.
In ordinary horticultural practice it is desirable to give some
guarantee as to what may be expected to come from the seeds of brightly
striped flowers. Neither the pure red type, nor the nearly yellow
racemes are the object of the culture, as both of them may be had pure
from their, own separate varieties. In order to insure proper striping,
both extremes are usually rejected and should be rooted out as soon as
the flowering period begins. Similarly the broad-striped ones should be
rejected, as they give a too large amount of uniform red flowers.
Clearly, but not broadly striped individuals always yield the most
reliable seed.
Summing up once more the results of our pedigree-experiment, we may
assert that the striped variety of the snapdragon is wholly permanent,
including the two opposite types of uniform color and of stripes. It
must have been so since it first originated from the invariable uniform
[322] varieties, about the middle of the last century, in the nursery of
Messrs. Vilmorin, and probably it will remain so as long as popular
taste supports its cultivation. It has never been observed to transgress
its limits or to sport into varieties without reversions or sports. It
fluctuates from one extreme to the other yearly, always recurring in the
following year, or even in the same summer by single buds. Highly
variable within its limits, it is absolutely constant or permanent, when
considered as a definite group.
Similar cases occur not rarely among cultivated plants. In the wild
state they seem to be wholly wanting. Neither are they met with as
occasional anomalies nor as distinct varieties. On the contrary, many
garden-flowers that are colored in the species, and besides this have a
white or yellow variety, have also striped sorts. The oldest instance is
probably the marvel of Peru, _Mirabilis Jalappa_, which already had more
than one striped variety at the time of its introduction from Peru into
the European gardens, about the beginning of the seventeenth century.
Stocks, liver-leaf (_Hepatica_), dame's violet (_Hesperis_), Sweet
William (_Dianthus barbatus_), and periwinkles (_Vinca minor_) seem to
be in the same condition, as their striped varieties were already quoted
[323] by the writers of the same century. Tulips, hyacinths, _Cyclamen_,
_Azalea_, _Camellia_, and even such types of garden-plants as the meadow
crane's-bill (_Geranium pratensev) have striped varieties. It is always
the red or blue color which occurs in stripes, the underlying ground
being white or yellow, according to the presence or absence of the
yellow in the original color mixture.
All these varieties are known to be permanent, coming true during long
series of successive generations. But very little is known concerning
the more minute details of their hereditary qualities. They come from
seed, when this is taken from striped individuals, and thence revert
from time to time to the corresponding monochromatic type. But whether
they would do so when self-fertilized, and whether the reversionary
individuals are always bound to return towards the center of the group
or towards the opposite limit, remains to be investigated. Presumably
there is nowhere a real transgression of the limits, and never or only
very rarely and at long intervals of time a true production of another
race with other hereditary qualities.
In order to satisfy myself on these points, I made some
pedigree-cultures with the striped forms of dame's violet (_Hesperis
matronalis_) [324] and of _Clarkia pulchella_. Both of them are
ever-sporting varieties. The experiments were conducted during five
generations with the violet, and during four with the striped Clarkia,
including the progeny of the striped and of the monochromatic red
offspring of a primitive striped plant. I need not give the figures here
for the numerical relations between the different types of each group,
and shall limit myself to the statement that they behaved in exactly the
same manner as the snapdragon.
It is worth while to dwell a moment on the capacity of the individuals
with red flowers to reproduce the striped type among their offspring.
For it is manifest that this latter quality must have lain dormant in
them during their whole life. Darwin has already pointed out that when a
character of a grandparent, which is wanting in the progeny, reappears
in the second generation, this quality must always be assumed to have
been present though latent in the intermediate generation. To the many
instances given by him of such alternative inheritance, the
monochromatic reversionists of the striped varieties are to be added as
a new type. It is moreover, a very suggestive type, since the latency is
manifestly of quite another character than for instance in the case of
Mendelian hybrids, and probably more allied to those instances, [325]
where secondary sexual marks, which are as a rule only evolved by one
sex, are transferred to the offspring through the other.
Stripes are by no means limited to flowers. They may affect the whole
foliage, or the fruits and the seeds, and even the roots. But all such
cases occur much more rarely than the striped flowers. An interesting
instance of striped roots is afforded by radishes. White and red
varieties of different shapes are cultivated. Besides them sometimes a
curious motley sort may be seen in the markets, which is white with red
spots, which are few and narrow in some samples, and more numerous and
broader in others. But what is very peculiar and striking is the
circumstance, that these stripes do not extend in a longitudinal, but in
a transverse direction. Obviously this must be the effect of the very
notable growth in thickness. Assuming that the colored regions were
small in the beginning, they must have been drawn out during the process
of thickening of the root, and changed into transverse lines. Rarely a
streak may have had its greatest extension in a transverse direction
from the beginning, in which case it would only be broadened and not
definitely changed in its direction.
This variety being a very fine one, and more agreeable to the eye than
the uniform colors, is [326] being more largely cultivated in some
countries. It has one great drawback: it never comes wholly true from
seed. It may be grown in full isolation, and carefully selected, all red
or nearly monochromatic samples being rooted out long before blooming,
but nevertheless the seed will always produce some red roots. The most
careful selection, pursued through a number of years, has not been
sufficient to get rid of this regular occurrence of reversionary
individuals. Seed-growers receive many complaints from their clients on
this account, but they are not able to remove the difficulty. This
experience is in full agreement with the experimental evidence given by
the snapdragon, and it would certainly be very interesting to make a
complete pedigree-culture with the radishes to test definitely their
compliance with the rules observed for striped flowers.
Horticulturists in such cases are in the habit of limiting themselves to
the sale of so-called mixed seeds. From these no client expects purity,
and the normal and hereditary diversity of types is here in some sense
concealed under the impurities included in the mixture from lack of
selection. Such cases invite scrutiny, and would, no doubt, with the
methods of isolation, artificial pollination, and the sowing of the
seeds separately from each parent, yield [327] results of great
scientific value. Any one who has a garden, and sufficient perseverance
to make pure cultures during a series of years might make important
contributions to scientific knowledge in this way.
Choice might be made from among a wide range of different types. A
variety of corn called "Harlequin" shows stripes on its kernels, and one
ear may offer nearly white and nearly red seeds and all the possible
intermediate steps between them. From these seeds the next generation
will repeat the motley ears, but some specimens will produce ears of
uniform kernels of a dark purple, showing thus the ordinary way of
reversion. Some varieties of beans have spotted seeds, and among a lot
of them one may be sure to find some purely red ones. It remains to be
investigated what will be their offspring, and whether they are due to
partial or to individual variation.
The cockscomb (_Celosia cristata_) has varieties of nearly all colors
from white and yellow to red and orange, and besides them some striped
varieties occur in our gardens, with the stripes going from the lower
parts of the stem up to the very crest of the comb. They are on sale as
constant varieties, but nothing has as yet been recorded concerning
their peculiar behavior in the inheritance of the stripes. [328] Striped
grapes, apples and other fruits might be mentioned in this connection.
Before leaving the striped varieties, attention is called to an
interesting deduction, which probably gives an explanation of one of the
most widely known instances of ever-sporting garden plants. Striped
races always include two types. Both of them are fertile, and each of
them reproduces in its offspring both its own and the alternate type. It
is like a game of ball, in which the opposing parties always return the
ball. But now suppose that only one of the types were fertile and the
other for some reason wholly sterile, and assume the reversionary, or
primitive monochromatic individuals to be fertile, and the derivative
striped specimens to bloom without seed. If this were the case,
knowledge concerning the hereditary qualities would be greatly limited.
In fact the whole pedigree would be reduced to a monochromatic strain,
which would in each generation sport in some individuals into the
striped variety. But, being sterile, they would not be able to propagate
themselves.
Such seems to be the case with the double flowered stocks. Their double
flowers produce neither stamens nor pistils, and as each individual is
either double or single in all its flowers, the doubles are wholly
destitute of seed. [329] Nevertheless, they are only reproduced by seed
from single flowers, being an annual or biennial species.
Stocks are a large family, and include a wonderful variety of colors,
ranging from white and yellow to purple and red, and with some
variations toward blue. They exhibit also diversity in the habit of
growth. Some are annuals, including the ten-week and pyramidal forms;
others are intermediates and are suitable for pot-culture; and the
biennial sorts include the well-known "Brompton" and "Queen" varieties.
Some are large and others are small or dwarf. For their brightness,
durability and fragrance, they are deservedly popular. There are even
some striped varieties. Horticulturists and amateurs generally know that
seed can be obtained from single stocks only, and that the double
flowers never produce any. It is not difficult to choose single plants
that will produce a large percentage of double blossoms in the following
generation. But only a percentage, for the experiments of the most
skilled growers have never enabled them to save seed, which would result
entirely in double flowering plants. Each generation in its turn is a
motley assembly of singles and doubles.
Before looking closer into the hereditary peculiarities of this old and
interesting ever-sporting [330] variety, it may be as well to give a
short description of the plants with double flowers. Generally speaking
there are two principal types of doubles. One is by the conversion of
stamens into petals, and the other is an anomaly, known under the name
of _petalomany_.
The change of stamens into petals is a gradual modification. All
intermediate steps are easily to be found. In some flowers all stamens
may be enlarged, in others only part of them. Often the broadened
filaments bear one or two fertile anthers. The fertility is no doubt
diminished, but not wholly destroyed. Individual specimens may occur,
which cannot produce any seed, but then others of the same lot may be as
fertile as can be desired. As a whole, such double varieties are
regularly propagated by seed.
Petalomany is the tendency of the axis of some flowers never to make any
stamens or pistils, not even in altered or rudimentary form. Instead of
these, they simply continue producing petals, going on with this
production without any other limit than the supply of available food.
Numerous petals fill the entire space within the outer rays, and in the
heart of the flower innumerable young ones are developed half-way, not
obtaining food enough to attain [331] full size. Absolute sterility is
the natural consequence of this state of things.
Hence it is impossible to have races of petalomanous types. If the
abnormality happens to show itself in a species, which normally
propagates itself in an asexual way, the type may become a vegetative
variety, and be multiplied by bulbs, buds or cuttings, etc. Some
cultivated anemones and crowfoots (_Ranunculus_) are of this character,
and even the marsh-marigold (_Caltha palustris_) has a petalomanous
variety. I once found in a meadow such a form of the meadow-buttercup
(_Ranunculus_ acris_), and succeeded in keeping it in my garden for
several years, but it did not make seeds and finally died. Camellias are
known to have both types of double flowers. The petalomanous type is
highly regular in structure, so much so as to be too uniform in all its
parts to be pleasing, while the conversion of stamens into petals in the
alternative varieties gives to these flowers a more lively diversity of
structure. Lilies have a variety called _Lilium candidum flore pleno_,
in which the flowers seem to be converted into a long spike of bright,
white narrow bracts, crowded on an axis which never seems to cease their
production.
It is manifestly impossible to decide how all such sterile double
flowers have originated. [332] Perhaps each of them originally had a
congruent single-flowered form, from which it was produced by seed in
the same way as the double stocks now are yearly. If this assumption is
right, the corresponding fertile line is now lost; it has perhaps died
out, or been masked. But it is not absolutely impossible that such
strains might one day be discovered for one or another of these now
sterile varieties.
Returning to the stocks we are led to the conception that some varieties
are absolutely single, while others consist of both single-flowered and
double-flowered individuals. The single varieties are in respect to this
character true to the original wild type. They never give seed which
results in doubles, providing all intercrossing is excluded. The other
varieties are ever-sporting, in the sense of this term previously
assumed, but with the restriction that the sports are exclusively
one-sided, and never return, owing to their absolute sterility.
The oldest double varieties of stocks have attained an age of a century
and more. During all this time they have had a continuous pedigree of
fertile and single-flowered individuals, throwing off in each generation
a definite number of doubles. This ratio is not at all dependent on
chance or accident, nor is it even variable to a remarkable degree.
Quite on the contrary [333] it is always the same, or nearly the same,
and it is to be considered as an inherent quality of the race. If left
to themselves, the single individuals always produce singles and doubles
in the same quantity; if cultivated after some special method, the
proportion may be slightly changed, bringing the proportion of doubles
up to 60% or even more.
Ordinarily the single and double members of such a race are quite equal
in the remainder of their attributes, especially in the color of their
flowers. But this is not always the case. The colors of such a race may
repeat for themselves the peculiarities of the ever-sporting characters.
It often happens that one color is more or less strictly allied to the
doubles, and another to the singles. This sometimes makes it difficult
to keep the various colors true. There are certain sorts, which
invariably exhibit a difference in color between the single and the
double flowers. The sulphur-yellow varieties may be adduced as
illustrative examples, because in them the single flowers always come
white. Hence in saving seed, it is impossible so to select the plant,
that an occasional white does not also appear among the double flowers,
agreeing in this deviation with the general rule of the eversporting
varieties.
I commend all the above instances to those [334] who wish to make
pedigree-cultures. The cooperation of many is needed to bring about any
notable advancement, since the best way to secure isolation is to
restrict one's self to the culture of one strain, so as to avoid the
intermixture of others. So many facts remain doubtful and open to
investigation, that almost any lot of purchased seed may become the
starting point for interesting researches. Among these the
sulphur-yellow varieties should be considered in the first place.
In respect to the great questions of heredity, the stocks offer many
points of interest. Some of these features I will now try to describe,
in order to show what still remains to be done, and in what manner the
stocks may clear the way for the study of the ever-sporting varieties.
The first point, is the question, which seeds become double-flowered and
which single-flowered plants? Beyond all doubt, the determination has
taken place before the ripening of the seed. But though the color of the
seed is often indicative of the color of the flowers, as in some red or
purple varieties, and though in balsams and some other instances the
most "highly doubled" flowers are to be obtained from the biggest and
plumpest seeds, no such rule seems to exist respecting the double
stocks. Now if one half of the seeds gives doubles, and [335] the other
half singles, the question arises, where are the singles and the doubles
to be found on the parent-plant?
The answer is partly given by the following experiment. Starting from
the general rule of the great influence of nutrition on variability, it
may be assumed that those seeds will give most doubles, that are best
fed. Now it is manifest that the stem and larger branches are, in a
better condition than the smaller twigs, and that likewise the first
fruits have better chances than the ones formed later. Even in the same
pod the uppermost seeds will be in a comparatively disadvantageous
position. This conception leads to an experiment which is the basis of a
practical method much used in France in order to get a higher percentage
of seeds of double-flowering plants.
This method consists in cutting off, in the first place the upper parts
of all the larger spikes, in the second place, the upper third part of
each pod, and lastly all the small and weak twigs. In doing so the
percentage is claimed to go up to 67-70%, and in some instances even
higher. This operation is to be performed as soon as the required number
of flowers have ceased blossoming. All the nutrient materials, destined
for the seeds, are now forced to flow into these relatively few embryos,
and it is clear that [336] they will be far better nourished than if no
operation were made.
In order to control this experiment some breeders have made the
operation on the fruits when ripe, instead of on the young pods, and
have saved the seeds from the upper parts separately. This seed,
produced in abundance, was found to be very poor in double flowers,
containing only some 20-30%. On the contrary the percentage of doubles
in the seed of the lower parts was somewhat augmented, and the average
of both would have given the normal proportion of 50%.
Opposed to the French method is the German practice of cultivating
stocks, as I have seen it used on a very large scale at Erfurt and at
other places. The stocks are grown in pots on small scaffolds, and not
put on or into the earth. The obvious aim of this practice is to keep
the earth in the pots dry, and accordingly they are only scantily
watered. In consequence they cannot develop as fully as they would have
done when planted directly in the beds, and they produce only small
racemes and no weak twigs, eliminating thereby without further operation
the weaker seeds as by the French method. The effect is increased by
planting from 6-10 separate plants in each pot.
It would be very interesting to make comparative [337] trials of both
methods, in order to discover the true relation between the practice and
the results reached. Bath should also be compared with cultures on open
plots, which are said to give only 50% of doubles. This last method of
culture is practiced wherever it is desired to produce great quantities
of seeds at a low cost. Such trials would no doubt give an insight into
the relations of hereditary characters to the distribution of the food
within the plant.
A second point is the proportional increase of the double-flowering
seeds with age. If seed is kept for two or three years, the greater part
of the grains will gradually die, and among the remainder there is found
on sowing, a higher percentage of double ones. Hence we may infer that
the single-flowered seeds are shorter lived than the doubles, and this
obviously points to a greater weakness of the first. It is quite evident
that there is some common cause for these facts and for the above cited
experience, that the first and best pods give more doubles. Much,
however, remains to be investigated before a satisfactory answer can be
made to these questions.
A third point is the curious practice, called by the French "esimpler,"
and which consists in pulling out the singles when very young. It seems
to be done at an age when the flower-buds [338] are not yet visible, or
at least are not far enough developed to show the real distinctive
marks. Children may be employed to choose and destroy the singles. There
are some slight differences in the fullness and roundness of the buds
and the pubescence of the young leaves. Moreover the buds of the doubles
are said to be sweeter to the taste than those of the singles. But as
yet I have not been able to ascertain, whether any scientific
investigation of this process has ever been made, though according to
some communications made to me by the late Mr. Cornu, the practice seems
to be very general in the environs of Paris. In summer large fields may
be seen, bearing exclusively double flowers, owing to the weeding out of
the singles long before flowering.
Bud-variation is the last point to be taken up. It seems to be very rare
with stocks, but some instances have been recorded in literature. Darwin
mentions a double stock with a branch bearing single flowers, and other
cases are known to have occurred. But in no instance does the seed of
such a bud-variant seem to have been saved. Occasionally other
reversions also occur. From time to time specimens appear with more
luxurious growth and with divergent instead of erect pods. They are
called, in Erfurt, "generals" on account [339] of their stiff and erect
appearance, and they are marked by more divergent horns crowning the
pods. They are said to produce only a relatively small number of doubles
from their seeds, and even this small number might be due to
fertilization with pollen of their neighbors. I saw some of these
reversionary types; when inspecting the nurseries of Erfurt, but as they
are, as a rule, thrown out before ripening their seed, nothing is
exactly known about their real hereditary qualities.
Much remains to be cleared up, but it seems that one of the best means
to find a way through the bewildering maze of the phenomena of
inheritance, is to make groups of related forms and to draw conclusions
from a comparison of the members of such groups. Such comparisons must
obviously give rise to questions, which in their turn will directly lead
to experimental investigation.
[340]