Mutations occur as often among cultivated plants as among those in the
wild state. Garden flowers are known to vary markedly. Much of their
variability, however, is due to hybridism, and the combination of
characters previously separate has a value for the breeder nearly equal
the production of really new qualities. Nevertheless there is no doubt
that some new characters appear from time to time.
In a previous lecture we have seen that varietal characters have many
features in common. One of them is their frequent recurrence both in the
same and in other, often very distantly related, species. This
recurrence is an important factor in the choice of the material for an
experimental investigation of the nature of mutations.
Some varieties are reputed to occur more often and more readily than
others. White-colored varieties, though so very common, seem for the
most part to be of ancient date, but only few [489] have a known origin,
however. Without any doubt many of them have been found in a wild state
and were introduced into culture. On the other hand double flowers are
exceedingly rare in the wild state, and even a slight indication of a
tendency towards doubling, the stray petaloid stamens, are only rarely
observed growing wild. In cultivation, however, double flowers are of
frequent occurrence; hence the conclusion that they have been produced
in gardens and nurseries more frequently than perhaps any other type of
variety.
In the beginning of my experimental work I cherished the hope of being
able to produce a white variety. My experiments, however, have not been
successful, and so I have given them up temporarily. Much better chances
for a new double variety seemed to exist, and my endeavors in this
direction have finally been crowned with success.
For this reason I propose to deal now with the production of double
flowers, to inquire what is on record about them in horticultural
literature, and to give a full description of the origin thereof in an
instance which it was my good fortune to observe in my garden.
Of course the historical part is only a hasty survey of the question and
will only give such evidence as may enable us to get an idea of the
[490] chances of success for the experimental worker. In the second half
of the seventeenth century (1671), my countryman, Abraham Munting,
published a large book on garden plants with many beautiful figures. It
is called "Waare Oeffeninge der Planters," or "True Exercises With
Plants." The descriptions pertain to ordinary typical species in greater
part, but garden varieties receive special attention. Among these a long
list of double flowers are to be seen. Double varieties of poppies,
liverleaf (Hepatica), wallflowers (_Cheiranthus_), violets, _Caltha_,
_Althaea_, _Colchicum_, and periwinkles (_Vinca_), and a great many
other common flowers were already in cultivation at that time.
Other double forms have been since added. Many have been introduced from
Japan, especially the Japanese marigold, _Chrysanthemum indicum_. Others
have been derived from Mexico, as for instance the double zinnias. The
single dahlias only seem to have been originally known to the
inhabitants of Mexico. They were introduced into Spain at about 1789,
and the first double ones were produced in Louvain, Belgium, in 1814.
The method of their origin has not been described, and probably escaped
the originators themselves. But in historical records we find the
curious statement that it took place after three years' work. This
indicates [491] a distinct plan, and the possibility of carrying it to a
practical conclusion within a few years' time.
Something more is known about other cases. Garden anemones, _Anemone
coronaria_, are said to have become double in the first half of the last
century in an English nursery. The owner, Williamson, observing in his
beds a flower with a single broadened stamen, saved its seeds
separately, and in the next generations procured beautifully filled
flowers. These he afterwards had crossed by bees with a number of
colored varieties, and in this way succeeded in producing many new
double types of anemone.
The first double petunia is known to have suddenly and accidentally
arisen from ordinary seed in a private garden at Lyons about 1855. From
this one plant all double races and-varieties have been derived by
natural and partly by artificial crosses. Carriere, who reported this
fact, added that likewise other species were known at that time to
produce new double varieties rapidly. The double fuchsias originated
about the same time (1854) and ten years later the range of double
varieties of this plant had become so large that Carriere found it
impossible to enumerate all of them.
Double carnations seem to be relatively old, double corn-flowers and
double blue-bells being [492] of a later period. A long list could
easily be made, to show that during the whole history of horticulture
double varieties have arisen from time to time. As far as we can judge,
such appearances have been isolated and sudden. Sometimes they sprang
into existence in the full display of their beauty, but most commonly
they showed themselves for the first time, exhibiting only spare
supernumerary petals. Whenever such sports were worked up, a few years
sufficed to reach the entire development of the new varietal attribute.
From this superficial survey of historical facts, the inference is
forced upon us that the chance of producing a new double variety is good
enough to justify the attempt. It has frequently succeeded for practical
purposes, why should it not succeed as well for purely scientific
investigation? At all events the type recommends itself to the student
of nature, both on account of its frequency, and of the apparent
insignificance of the first step, combined with the possibility of
rapidly working up from this small beginning of one superfluous petal
towards the highest degree of duplication.
Compared with the tedious experimental production of the peloric
toad-flax, the attempt to produce a double flower has a distinct
attraction. The peloric toad-flax is nothing new; the [493] experiment
was only a repetition of what presumably takes place often within the
same species. To attempt to produce a double variety we may choose any
species, and of course should select one which as yet has not been known
to produce double flowers. By doing so we will, if we succeed, produce
something new. Of course, it does not matter whether the new variety has
an horticultural interest or not, and it seems preferable to choose a
wild or little cultivated species, to be quite sure that the variety in
question is not already in existence. Finally the prospect of success
seems to be enhanced if a species is chosen, the nearest allies of which
are known to have produced double flowers.
For these reasons and others I chose for my experiment the
corn-marigold, or _Chrysanthemum segetum_. It is also called the golden
cornflower. In the wheat and rye fields of central Europe it associates
with the blue-bottle or blue corn-flower. It is sometimes cultivated and
the seeds are offered for sale by many nurserymen. It has a cultivated
variety, called _grandiflorum_, which is esteemed for its brilliancy and
long succession of golden bloom. This variety has larger flower-heads,
surrounded with a fuller border of ray-florets. The species belongs to a
genus many species of which have produced [494] double varieties. One of
them is the Japanese marigold, others are the _carinatum_ and the
_imbricatum_ species. Nearly allied are quite a number of garden-plants
with double flower-heads, among which are the double camomiles.
My attention was first drawn to the structure of the heads and
especially to the number of the ray-florets of the corn-marigold. The
species appertains to that group of composites which have a head of
small tubular florets surrounded by a broad border of rays. These rays,
when counted, are observed to occur in definite numbers, which are
connected with each other by a formula, known as "the series" of Braun
and Schimper. In this formula, which commences with 1 and 2, each number
is equal to the sum of the two foregoing figures. Thus 5, 8 and 13 are
very frequent occurrences, and the following number, 21, is a most
general one for apparently full rays, such as in daisies, camomiles,
_Arnica_ and many other wild and cultivated species.
These numbers are not at all constant. They are only the averages,
around which the real numbers fluctuate. There may even be an
overlapping of the extremes, since the fluctuation around 13 may even go
beyond 8 and 21, and so on. But such extremes are only found in stray
flowers, occurring on the same [495] individuals with the lesser degrees
of deviation.
Now the marigold averages 13, and the _grandiflorum_ 21 rays. The wild
species is pure in this respect, but the garden-variety is not. The
seeds which are offered for sale usually contain a mixture of both forms
and their hybrids. So I had to isolate the pure types from this mixture
and to ascertain their constancy and mutual independency. To this end I
isolated from the mixture first the 13-rayed, and afterwards the
21-rayed types. As the marigolds are not sufficiently self-fertile, and
are not easily pollinated artificially, it seemed impossible to carry on
these two experiments at the same time and in the same garden. I devoted
the first three years to the lower form, isolated some individuals with
12-13 rays out of the mixture of 1892 and counted the ray-florets on the
terminal head of every plant of the ensuing generation next year. I
cultivated and counted in this way above 150 individuals and found an
average of exactly 13 with comparatively few individuals displaying 14
or only 12 rays, and with the remainder of the plants grouped
symmetrically around this average. I continued the experiment for still
another year and found the same group of figures. I was then satisfied
as to the purity of the isolated strain. Next year I sowed a new mixture
in [496] order to isolate the reputed pure _grandiflorum_ type. During
the beginning of the flowering period I ruthlessly threw away all plants
displaying less than 21 rays in the first or terminal head. But this
selection was not to be considered as complete, because the 13-rayed
race may eventually transgress its boundary and come over to the 21 and
more. This made a second selection necessary. On the selected plants all
the secondary heads were inspected and their ray-florets counted. Some
individuals showed an average of about 13 and were destroyed. Others
gave doubtful figures and were likewise eliminated, and only 6 out of a
lot of nearly 300 flowering plants reached an average of 21 for all of
the flowers.
Our summer is a short one, compared with the long and beautiful summer
of California, and it was too late to cut off the faded and the open
flowers, and await new ones, which might be purely fertilized after the
destruction of all minor plants. So I had to gather the seed from
flowers, which might have been partially fertilized by the wrong pollen.
This however, is not so great a drawback in selection experiments as
might be supposed at first sight. The selection of the following year is
sure to eliminate the offspring of such impure parentage.
[497] A far more important principle is that of the hereditary
percentage, already discussed in our lecture on the selection of
monstrosities. In our present case it had to be applied only to the six
selected plants of 1895. To this end the seeds of each of them were sown
separately, the ray-florets of the terminal heads of each of the new
generation were counted, and curves and averages were made up for the
six groups. Five of them gave proof of still being mixtures and were
wholly rejected. The children of the sixth parent, however, formed a
group of uniform constitution, all fluctuating around the desired
average of 21. All in all the terminal heads of over 1,500 plants have
been subjected to the somewhat tedious work of counting their
ray-florets. And this not in the laboratory, but in the garden, without
cutting them off. Otherwise it would obviously have been impossible to
recognize the best plants for preservation. I chose only two plants
which in addition recommended themselves by the average number of rays
on their secondary heads, sowed their seeds next year separately and
compared the numerical constitution of their offspring. Both groups
averaged 21 and were distributed very symmetrically around this mean.
This result [498] showed that no further selection could be of any
avail, and that I had succeeded in purifying the 21-rayed _grandiflorum_
variety.
It is from this _grandiflorum_ that I have finally produced my double
variety. In the year 1896 I selected from among the above quoted 1,500
plants, 500 with terminal heads bearing 21 or more rays. On these I
counted the rays of all the secondary heads about the middle of August
(1896) and found that they had, as a rule, retrograded to lower figures.
On many thousands of heads only two were found having 22 rays. All
others had the average number of 21 or even less. I isolated the
individual which bore these two heads, allowed them to be fertilized by
insects with the pollen of some of the best plants of the same group,
but destroyed the remainder.
This single exceptional plant has been the starting point of my double
variety. It was not remarkable for its terminal head, which exhibited
the average number of rays of the 21-rayed race. Nor was it
distinguished by the average figure for all its heads. It was only
selected because it was the one plant which had some secondary heads
with one ray more than all the others. This indication was very slight,
and could not have been detected save by the counting of the rays of
thousands of heads.
[499] But the rarity of the anomaly was exactly the indication wanted,
and the same deviation would have had no signification whatever, had it
occurred in a group fluctuating symmetrically around the average figure.
On the other hand, the observed anomaly was only an indication, and no
guarantee of future developments.
Here it should be remarked that the indication alluded to was not the
appearance of the expected character of doubling in ever so slight a
measure. It was only a guide to be followed in further work. The real
character of double flower-heads among composites lies in the production
of rays on the disk. No increase of the number of the outer rays can
have the same significance. A hasty inspection of double flower heads
may convey the idea that all rays are arranged around a little central
cluster of disk-florets, the remainder of the original disk-florets but
a closer investigation will always reveal the fallacy of this
conclusion. Hidden between the inner rays, and covered by them, lie the
little tubular and fertile florets everywhere on the disk. They may not
be easily seen, but if the supernumerary rays are pulled out, the disk
may be seen to bear numerous small florets at intervals. But these
intervals are not at all numerous, showing thereby that only a
relatively small number of tubes has been [500] converted into rays.
This conversion is obviously the true mark of the doubling, and before
traces of it are found, no assertion whatever can be given as to the
issue of the pedigree experiment.
Three more years were required before this first, but decisive trace was
discovered. During these years I subjected my strain to the same sharp
selection as has already been described. The chosen ancestor of the race
had flowered in 1896, and the next year I sowed its seeds only. From
this generation I chose the one plant with the largest number of rays in
its terminal head, and repeated this in the following year.
The consequence was that the average number of rays increased rapidly,
and with it the absolute maximum of the whole strain. The average came
up from 21 to 34. Brighter and brighter crowns of the yellow rays
improved my race, until it became difficult and very time consuming to
count all the large rays of the borders. The largest numbers determined
in the succeeding generations increased by leaps from 21 to 34 in the
first year, and thence to 48 and 66 in the two succeeding summers. Every
year I was able to save enough seed from the very best plant and to use
it only for the continuance of the race. Before the selected plants were
allowed to open the flowers from which the seed [501] was to be
gathered, nearly the whole remaining culture was exterminated, excepting
only some of the best examples, in order to have the required material
for cross-pollination by insects. Each new generation was thereby as
sharply selected as possible with regard to both parents.
All flower-heads were of course closely inspected. Not the slightest
indication of real doubling was discovered, even in the summer of 1899
in the fourth generation of my selected race. But among the best the new
character suddenly made its appearance. It was at the commencement of
September (1899), too late to admit of the seeds ripening before winter.
An inspection of the younger heads was made, which revealed three heads
with some few rays in the midst of the disk on one plant, the result of
the efforts of four years. Had the germ of the mutation lain hidden
through all this time? Had it been present, though dormant in the
original sample of seed? Or had an entirely new creation taken place
during my continuous endeavors? Perhaps as their more or less immediate
result? It is obviously impossible to answer these questions, before
further and similar experiments shall have been performed, bringing to
light other details that will enable us to reach a more definite
conclusion.
[502] The fact that the origination of such forms is accessible to
direct investigation is proven quite independently of all further
considerations. The new variety came into existence at once. The leap
may have been made by the ancestor of the year 1895, or by the plant of
1899, which showed the first central rays, or the sport may have been
gradually built up during those four years. In each case there was a
leap, contrasting with the view which claims a very long succession of
years for the development of every new character.
Having discovered this first trace of doubling, it was to be expected
that the new variety would be at once as pure and as rich as other
double composites usually are. Some effect of the crossing with the
other seed-bearing individuals might still disturb this uniformity in
the following year, but another year's work would eliminate even this
source of impurity.
These two years have given the expected result. The average number of
the rays, which had already arisen from 13 to 34 now at once came up to
47 and 55, the last figure being the sum of 21 and 34 and therefore the
probable uttermost limit to be reached before absolute doubling. The
maximum numbers came as high as 100 in 1900, and reached even 200 in
1901. Such heads are as completely double as are the [503] brightest
heads of the most beautiful double commercial varieties of composites.
Even the best white camomiles (_Chrysanthemum inodorum_) and the
gold-flowers or garden-marigolds (_Calendula officinalis_) do not come
nearer to purity since they always have scores of little tubular florets
between the rays on their disks.
Real atavists or real reversionists were seen no more after the first
purification of the race. I have continued my culture and secured last
summer (1903) as many and as completely doubled heads as previously. The
race has at once become permanent and constant. It has of course a wide
range of fluctuating variability, but the lower limit has been worked up
to about 34 rays, a figure never reached by the _grandiflorum_ parent,
from which my new variety is thus sharply separated.
Unfortunately the best flowers and even the best individuals of my race
are wholly barren. Selection has reached its practical limit. Seeds must
be saved from less dense heads, and no way has been found of avoiding
it. The ray-florets are sterile, even in the wild species, and when
growing in somewhat large numbers on the disk, they conceal the fertile
flowers from the visiting insects, and cause them also to be sterile.
The same is the case with the best cultivated forms. Their showiest
individuals are [504] barren, and incapable of the reproduction of the
race.
This last is therefore, of necessity, always continued by means of
individuals whose deviation from the mean average is the least. But in
many cases the varieties are so highly differentiated that selection has
become quite superfluous for practical purposes. I have already
discussed the question as to the actual moment, in which the change of
the _grandiflorum_ variety into the new _plenum_ form must be assumed to
have taken place. In this respect some stress is to be laid on the fact
that the improvement through selection has been gradual and continuous,
though very rapid from the first moment. But with the appearance of the
first stray rays within the disk, this continuity suddenly changed. All
the children of this original mutated plant showed the new character,
the rays within the disk, without exception. Not on all the heads, nor
even on the majority of the heads on some individuals, but on some heads
all gave clear proof of the possession of the new attribute. This was
present in all the representatives of the new race, and had never been
seen in any of their parents and grandparents. Here there was evidently
a sudden leap, at least in the external form of the plants. And it seems
to me to be the most simple conception, [505] that this visible leap
directly corresponded to that inner change, which brought about the
complete inheritability of the new peculiarity. It is very interesting
to observe how completely my experience agrees with the results of the
observations of breeders at large. No doubt a comparison is difficult,
and the circumstances are not adequate to a close study.
Isolation and selection have been applied commonly only so far as was
consistent with the requirements of practical horticulture, and of
course a determination of the hereditary percentage was never made. The
disregard of this feature made necessary a greater length of time and a
larger number of generations to bring about the desired changes.
Notwithstanding this, however, it has been seen that double varieties
are produced suddenly. This may have occurred unexpectedly or after a
few years' effort toward the end desired. Whether this sudden appearance
is the consequence of a single internal differentiating step, or of the
rapid succession of lesser changes, cannot yet be made out. The extreme
variability of double flowers and the chance of their appearance with
only slight indications of the previous petaloid alterations of a few
stamens may often result in their origin being overlooked, while
subsequent generations may come in for full notice. [506] In the greater
number of cases recorded it remains doubtful whether the work said to be
done to obtain a new double variety was done before the appearance of
these preliminary indications or afterward.
In the first case, it would correspond with our selection of large
numbers of florets in the outer rays, in the second however, with the
ordinary purification of new races from hybrid mixtures.
In scientific selection-experiments such crosses are of course avoided,
and the process of purification is unnecessary, even as in the
_Chrysanthemum_ culture. The first generation succeeding the original
plant with disk-rays was in this respect wholly uniform and true to the
new type.
In practice the work does not start from such slight indications, and is
done with no other purpose in view than to produce double flowers in
species in which they did not already exist. Therefore it is of the
highest importance to know the methods used and the chances of success.
Unfortunately the evidence is very scanty on both points.
Lindley and other writers, on horticultural theory and practice assert
that a large amount of nourishment tends to produce double flowers,
while a culture under normal conditions, [507] even if the plants are
very strong and healthy, has no such effect. But even here it remains
doubtful whether it applies to the period before or after the internal
mutation. On the other hand success is not at all to be relied upon, nor
is the work to be regarded as easy. The instances of double flowers said
to be obtainable at will, are too rare in comparison with the number of
cases, where the first indication of them was found accidentally.
Leaving all these doubtful points, which will have to be cleared up by
further scientific investigation, the high degree of variability
requires further discussion. It may be considered from three different
points of view according to the limit of the deviation from the average,
to the dependency on external conditions and to periodicity. It seems
best to take up the last two points first.
On a visit to a nursery at Erfurt I once inspected an experiment with a
new double variety of the common blue-bottle or blue corn-flower. The
plants were dependent on the weather to a high degree. Bad weather
increased the number of poorly filled flower-heads, while warm and sunny
days were productive of beautiful double flowers. The heads that are
borne by strong branches have a greater tendency to become double than
those of the weaker ones, [508] and towards the autumn, when all those
of the first group are faded away, and only a weak though large section
of the heads is still flowering, the whole aspect of the variety
gradually retrogrades. The same law of dependency and periodicity is
prevalent everywhere. In my own cultures of the improved field-marigold
I have observed it frequently. The number of the ray-florets may be
considered as a direct response to nourishment, both when this is
determined by external circumstances, and when it depends on the
particular strength of the branch, which bears the head in question. It
is a case exactly similar to that of the supernumerary carpels of the
pistilloid poppy, and the deductions arrived at with that variety may be
applied directly to double flowers.
This dependency upon nourishment is of high practical importance in
combination with the usual effect of the doubling which makes the
flowers sterile. It is a general rule that the most perfect flowers do
not produce seed. At the height of the flowering period the external
circumstances are the most favorable, and the flowering branches still
constitute the stronger axes of the plants. Hence we may infer that
sterility will prevail precisely in this period. Many varieties are
known to yield only seeds from the very last flowers, as for instance
some [509] double begonias. Others bear only seed on their weaker
lateral branches, as the double camomile, or become fertile only towards
the fall, as is often the case with the above quoted Erfurt variety of
the blue-bottle. As far as I have been able to ascertain, such seeds are
quite adequate for the reproduction and perpetuation of the double
varieties, but the question whether there are differences between the
seeds of the more or less double flowers of the same plants still
remains open. It is very probable, from a theoretical point of view,
that such differences exist, but perhaps they are so slight, as to have
practically no bearing on the question.
On the ground of their wide range of variability, the double varieties
must be regarded as pertaining to the group of ever-sporting forms. On
one side they fluctuate in the direction towards such petalomanous
flowers as are borne by the stocks and others, which we have previously
discussed. Here no trace of the fertile organs is left. But this extreme
is never reached by petaloid double flowers. A gap remains which, often
overlooked, always exists, and which sharply separates the two types. On
the other hand the alteration of the stamens gradually relapses to
perfectly single flowers. Here the analogy with the pistillody of the
poppies and with the "five-leaved" clover is obvious.
[510] This conception of the inner nature of double flowers explains the
fact that the varietal mark is seldom seen to be complete throughout
larger groups of individuals, providing these have not been already
selected by this character. _Tagetes africana_ is liable to produce some
poorly filled specimens, and some double varieties of carnations are
offered for sale with the note that the seed yields only 80% of doubles.
With _Chrysanthemum coronarium_ and blue-bottles this figure is often
announced to be only about 50%. No doubt it is partly due to impurities,
caused by vicinism, but it is obviously improbable that the effect of
these impurities should be so large.
Some cases of partial reversion may be interpreted in the same way.
Among the garden anemones, _Anemone coronaria_, there is a variety
called the "Bride," on account of its pure white dowers. It is for sale
with single and with double flowers, and these two forms are known to
sport into one another, although they are multiplied in the vegetative
way. Such cases are known to be of quite ordinary occurrence. Of course
such sports must be considered as partial, and the same stem may bear
both types of flowers. It even happens that some particular flower is
partly double and partly single. Mr. Krelage, of Haarlem, had the
kindness to [511] send me such a curious flower. One half of it was
completely double, while the other half was entirely single, bearing
normal and fertile stamens in the ordinary number.
The same halfway doubling is recorded to occur among composites
sometimes, and from the same source I possess in my collection a head of
_Pyrethrum roseum_, bearing on half of its disk elongated corolla tubes,
and on the other half the small disk-florets of the typical species.
It is a current belief, that varieties are improved by continued
culture. I have never been able to ascertain the grounds on which this
conviction rests. It may be referred either to the purity of the race or
to the complete development of the varietal character. In the first case
it is a question of hybrid mixtures from which many young varieties must
be freed before being placed on the market. But as we have already seen
in a former lecture, this requires only three or four years, and
afterwards the degree of purity is kept up to the point which proves to
be the most suitable for practical purposes. The complete development of
the varietal character is a question restricted to ever-sporting
varieties, since in white flowers and other constant varieties this
degree is variable in a very small and unimportant measure. [512] Hence
the double flowers seem to afford a very good example for this
discussion.
It can be decided by two facts. First by a consideration of the oldest
double varieties, and secondly by that of the very youngest. Are the
older ones now in a better condition than at the outset? Have they
really been gradually improved during the centuries of their existence?
Obviously this can only be answered by a comparison of the figures given
by older writers, with the varieties as they are now in culture.
Munting's drawings and descriptions are now nearly two centuries and a
half old, but I do not find any real difference between his double
varieties and their present representatives. So it is in other cases in
which improvements by crossing or the introduction of new forms does not
vitiate the evidence. Double varieties, as a rule, are exactly the same
now, as they were at the time of their first introduction.
If this were otherwise one would expect that young double varieties
should in the main display only slight grades of the anomaly, and that
they would require centuries to reach their full development. Nothing of
the kind is on record. On the contrary the newest double sorts are said
to be not only equal to their predecessors, but to excel them. As a rule
such claims may be exaggerated, but not to any great extent. [513] This
is proven in the simplest way by the result of our own experiment.
In the double field-marigold we have the very first generation of a
variety of pure and not hybrid origin. It shows the new attribute in its
full development. It has flower-heads nearly as completely filled as the
best double varieties of allied cultivated composites. In the second
generation it reached heads with 200 rays each, and much larger numbers
will seldom be seen in older species on heads of equal size. I have
compared my novelty with the choicest double camomiles and others, but
failed to discover any real difference. Improvement of the variety
developed in the experiments carried on by myself seems to be excluded
by the fact that it comes into conflict with the same difficulty that
confronts the older cultivated species, viz.: the increasing sterility
of the race.
It is perfectly evident that this double marigold is now quite constant.
Continuously varying about a fixed average it may live through
centuries, but the mean and the limits will always remain the same, as
in the case of the ever-sporting varieties.
Throughout this lecture I have spoken of double flowers and double
flower-heads of composites as of one single group. They are as nearly
related from the hereditary point of [514] view, as they are divergent
in other respects. It would be superfluous to dwell any longer upon the
difference between heads and flowers. But it is as well to point out,
that the term double flowers indicates a motley assemblage of different
phenomena. The hen-and-chicken daisy, and the corresponding variety of
the garden cineraria (_Cineraria cruenta_), are extremes on one side.
The hen-and-chicken type occurs even in other families and is known to
produce most curious anomalies, as with _Scabiosa_, the supernumerary
heads of which may be produced on long stalks and become branched
themselves in the same manner.
Petalody of the stamens is well known to be the ordinary type of
doubling. But it is often accompanied by a multiplication of the organs,
both of the altered stamens and of the petals themselves. This
proliferation may consist in median or in lateral cleavages, and in both
cases the process may be repeated one or more times. It would be quite
superfluous to give more details, which may be gathered from any
morphologic treatise on double flowers. But from the physiologic point
of view all these cases are to be considered as one large group,
complying with previously given definitions of the ever-sporting
varieties. They are very variable and wholly permanent. Obviously this
[515] permanency agrees perfectly with the conception of their sudden
origin.
[516]