In our experiments on the origin of peloric varieties and double flowers
we were guided in the choice of our material by a survey of the evidence
already at hand. We chose the types known to be most commonly produced
anew, either in the wild state or under the conditions of cultivation.
In both instances our novelty was a variety in the ordinary sense of the
word. Our pedigree-culture was mainly an experimental demonstration of
the validity of conclusions, which had previously been deduced from such
observations as can be made after the accidental birth of new forms.
From these facts, and even from these pedigree-experiments, it is
scarcely allowable to draw conclusions as to the origin of real species.
If we want to know how species originate, it is obviously necessary to
have recourse to direct observation. The question is of the highest
importance, both for the theory of descent, and for our conception of
the real nature of [517] systematic affinities at large. Many authors
have tried to solve it on the ground of comparative studies and of
speculations upon the biologic relations of plants and animals. But in
vain. Contradiction and doubt still reign supreme. All our hopes now
rest on the result of experiments.
Unfortunately such experiments seemed simply impossible a few years ago.
What is to guide us in the choice of the material? The answer may only
be expected from a consideration of elementary species. For it is
obvious that they only can be observed to originate, and that the
systematic species, because they are only artificial groups of lower
unities, can never become the subject of successful experimental
inquiry.
In previous lectures we tried to clear up the differences existing
between nearly related elementary species. We have seen that they affect
all of the attributes of the plants, each of them changing in some
measure all of the organs. Nevertheless they were due to distinct
unities and of the lowest possible degree. Such unit-steps may therefore
be expected to become visible some time or other by artificial means. On
the other hand, mutations as a rule make their appearance in groups, and
there are many systematic species which on close inspection [518] have
been shown to be in reality composite assemblages. Roses and brambles,
hawkweeds and willows are the best known examples. Violets and _Draba
verna_, dandelions and helianthemums and many other instances were dealt
with in previous lectures. Even wheat and barley and corn afford
instances of large groups of elementary species. Formerly mixed in the
fields, they became separated during the last century, and now
constitute constant races, which, for brevity's sake, are dealt with
under the name of varieties.
In such groups of nearly allied forms the single members must evidently
be of common origin. It is not necessary for them to have originated all
in the same place or at the same time. In some cases, as with _Draba
verna_, the present geographic distribution points to a common
birthplace, from whence the various forms may about the same period have
radiated in all directions. The violets on the other hand seem to
include widely diffused original forms, from which branches have started
at different times and in different localities.
The origin of such groups of allied forms must therefore be the object
of our research. Perhaps we might find a whole group, perhaps only part
of it. In my opinion we have the right to assume that if _Draba_ and
violets and [519] others have formerly mutated in this way, other
species must at present be in the same changeable condition. And if
mutations in groups, or such periodic mutations should be the rule, it
is to be premised that these periods recur from time to time, and that
many species must even now be in mutating condition, while others are
not.
It is readily granted that the constant condition of species is the
normal one, and that mutating periods must be the exception. This fact
does not tend to increase our prospect of discovering a species in a
state of mutability. Many species will have to be tested before finding
an instance. On the other hand, a direct trial seems to be the only way
to reach the goal. No such special guides as those that led us to the
choice of pelories and double flowers are available. The only indication
of value is the presumption that a condition of mutability might be
combined with a general state of variability at large, and that groups
of plants of very uniform features might be supposed to be constant in
this respect too. On the contrary, anomalies and deviations if existent
in the members of one strain, or found together in one native locality
of a species, might be considered as an indication in the desired
direction.
Few plants vary in the wild state in such a [520] measure as to give
distinct indications. All have to be given a trial in the garden under
conditions as similar as possible to their natural environments.
Cultivated plants are of course to be excluded. Practically they have
already undergone the experience in question and can not be expected to
change their habits soon enough. Moreover they are often of hybrid
origin. The best way is to experiment with the native plants of one's
own country.
I have made such experiments with some hundred species that grow wild in
Holland. Some were very variable, as for instance, the jointed charlock
(_Raphanus Raphanistrum_) and the narrow-leaved plantain (_Plantago
lanceolata_). Others seemed more uniform, but many species, collected
without showing any malformation, subsequently produced them in my
garden, either on the introduced plants themselves or among their
offspring. From this initial material I have procured a long series of
hereditary races, each with some peculiar anomaly for its special
character. But this result was only a secondary gain, a meager
consolation for the negative fact that no real mutability could be
discovered.
My plants were mostly annuals or biennials, or such perennials as under
adequate treatment might produce flowers and seeds during their [521]
first summer. It would be of no special use to enumerate them. The
negative result does not apply to the species as such, but only to the
individual strain, which I collected and cultivated. Many species, which
are quite constant with us, may be expected to be mutable in other parts
of their range.
Only one of all my tests met my expectations. This species proved to be
in a state of mutation, producing new elementary forms continually, and
it soon became the chief member of my experimental garden. It was one of
the evening primroses.
Several evening-primroses have at different times been introduced into
European gardens from America. From thence they have spread into the
vicinity, becoming common and exhibiting the behavior of indigenous
types. _Oenothera biennis_ was introduced about 1614 from Virginia, or
nearly three centuries ago. _O. muricata_, with small corollas and
narrow leaves, was introduced in the year 1789 by John Hunneman, and _O.
suaveolens_, or sweet-scented primrose, a form very similar to the
_biennis_, about the same time, in 1778, by John Fothergill. This form
is met with in different parts of France, while the _biennis_ and
_muricata_ are very common in the sandy regions of Holland, where I have
observed them for [522] more than 40 years. They are very constant and
have proven so in my experiments. Besides these three species, the
large-flowered evening-primrose, or _Oenothera lamarckiana_, is found in
some localities in Holland and elsewhere. We know little concerning its
origin. It is supposed to have come from America in the same way as its
congeners, but as yet I have not been able to ascertain on what grounds
this supposition rests. As far as I know, it has not been seen growing
wild in this country, though it may have been overlooked. The fact that
the species of this group are subject to many systematic controversies
and are combined by different writers into systematic species in
different ways, being often considered as varieties of one or two types,
easily accounts for it having been overlooked. However, it would be of
great interest to ascertain whether _O. lamarckiana_ yet grows in
America, and whether it is in the same state of mutability here as it is
in Holland.
The large-flowered evening-primrose was also cultivated about the
beginning of the last century in the gardens of the Museum d'Histoire
Naturelle, at Paris, where it was noticed by Lamarck, who at once
distinguished it as an undescribed species. He wrote a complete
description [523] of it and his type specimens are still preserved in
the herbarium of the Museum, where I have compared them with the plants
of my own culture. Shortly afterwards it was renamed by Seringe, in
honor of its eminent discoverer, whose name it now bears. So Lamarck
unconsciously discovered and described himself the plant, which after a
century, was to become the means of an empirical demonstration of his
far-reaching views on the common origin of all living beings.
_Oenothera lamarckiana_ is considered in Europe as a garden-plant, much
prized for parks and ornamental planting. It is cultivated by
seed-merchants and offered for sale. It has escaped from gardens, and
having abundant means for rapid multiplication, has become wild in many
places. As far as I know its known localities are small, and it is to be
presumed that in each of them the plant has escaped separately from
culture. It was in this state that I first met with this beautiful
species.
Lamarck's evening-primrose is a stately plant, with a stout stem,
attaining often a height of 1.6 meters and more. When not crowded the
main stem is surrounded by a large circle of smaller branches, growing
upwards from its base so as often to form a dense bush. These branches
in their turn have numerous lateral [524] branches. Most of them are
crowned with flowers in summer, which regularly succeed each other,
leaving behind them long spikes of young fruits. The flowers are large
and of a bright yellow color, attracting immediate attention, even from
a distance. They open towards evening, as the name indicates, and are
pollinated by humble-bees and moths. On bright days their duration is
confined to one evening, but during cloudy weather they may still be
found open on the following morning. Contrary to their congeners they
are dependent on visiting insects for pollination. _O. biennis_ and _O.
muricata_ have their stigmas in immediate contact with the anthers
within the flower-buds, and as the anthers open in the morning preceding
the evening of the display of the petals, fecundation is usually
accomplished before the insects are let in. But in _O. lamarckiana_ no
such self-fertilization takes place. The stigmas are above the anthers
in the bud, and as the style increases in length at the time of the
opening of the corolla, they are elevated above the anthers and do not
receive the pollen. Ordinarily the flowers remained sterile if not
visited by insects or pollinated by myself, although rare instances of
self-fertilization were seen.
In falling off, the flowers leave behind them a stout ovary with four
cells and a large number [525] of young seeds. The capsule when ripe,
opens at its summit with four valves, and contains often from two to
three hundred seeds. A hundred capsules on the main stem is an average
estimate, and the lateral branches may ripen even still more fruits, by
which a very rapid dissemination is ensured.
This striking species was found in a locality near Hilvers, in the
vicinity of Amsterdam, where it grew in some thousands of individuals.
Ordinarily biennial, it produces rosettes in the first, and stems in the
second year. Both the stems and the rosettes were at once seen to be
highly variable, and soon distinct varieties could be distinguished
among them.
The first discovery of this locality was made in 1886. Afterwards I
visited it many times, often weekly or even daily during the first few
years, and always at least once a year up to the present time. This
stately plant showed the long-sought peculiarity of producing a number
of new species every year. Some of them were observed directly on the
field, either as stems or as rosettes. The latter could be transplanted
into my garden for further observation, and the stems yielded seeds to
be sown under like control. Others were too weak to live a sufficiently
long time in the field. They were discovered by sowing seed from
indifferent plants [526] of the wild locality in the garden. A third and
last method of getting still more new species from the original strain,
was the repetition of the sowing process, by saving and sowing the seed
which ripened on the introduced plants. These various methods have led
to the discovery of over a dozen new types, never previously observed or
described.
Leaving the physiologic side of the relations of these new forms for the
next lecture, it would be profitable to give a short description of the
several novelties. To this end they may be combined under five different
heads, according to their systematic value. The first head includes
those which are evidently to be considered as varieties, in the narrower
sense of the word, as previously given. The second and third heads
indicate the real progressive elementary species, first those which are
as strong as the parent-species, and secondly a group of weaker types,
apparently not destined to be successful. Under the fourth head I shall
include some inconstant forms, and under the last head those that are
organically incomplete.
Of varieties with a negative attribute, or real retrograde varieties, I
have found three, all of them in a flowering condition in the field. I
have given them the names of _laevifolia_, _brevistylis_ and _nanella_.
[527] The _laevifolia_, or smooth-leaved variety, was one of the very
first deviating types found in the original field. This was in the
summer of 1887, seventeen years ago. It formed a little group of plants
growing at some distance from the main body, in the same field. I found
some rosettes and some flowering stems and sowed some seed in the fall.
The variety has been quite constant in the field, neither increasing in
number of individual plants nor changing its place, though now closely
surrounded by other _Lamarckiana_s. In my garden it has proved to be
constant from seed, never reverting to the original _lamarckiana_,
provided intercrossing was excluded.
It is chiefly distinguished from Lamarck's evening-primrose by its
smooth leaves, as the name indicates. The leaves of the original form
show numerous sinuosities in their blades, not at the edge, but anywhere
between the veins. The blade shows numbers of convexities on either
surface, the whole surface being undulated in this manner; it lacks also
the brightness of the ordinary evening-primrose or _Oenothera biennis_.
These undulations are lacking or at least very rare on the leaves of the
new _laevifolia_. Ordinarily they are wholly wanting, but at times
single leaves with slight manifestations of this [528] character may
make their appearance. They warn us that the capacity for such
sinuosities is not wholly lost, but only lies dormant in the new
variety. It is reduced to a latent state, exactly as are the apparently
lost characters of so many ordinary horticultural varieties.
Lacking the undulations, the _laevifolia_ leaves are smooth and bright.
They are a little narrower and more slender than those of the
_lamarckiana_. The convexities and concavities of leaves are said to be
useful in dry seasons, but during wet summers, such as those of the last
few years, they must be considered as very harmful, as they retain some
of the water which falls on the plants, prolonging the action of the
water on the leaves. This is considered by some writers to be of some
utility after slight showers, but was observed to be a source of
weakness during wet weather in my garden, preventing the leaves from
drying. Whether the _laevifolia_ would do better under such
circumstances, remains to be tested.
The flowers of the _laevifolia_ are also in a slight degree different
from those of _lamarckiana_. The yellow color is paler and the petals
are smoother. Later, in the fall, on the weaker side branches these
differences increase. The _laevifolia_ petals become smaller and are
often not emarginated at the apex, becoming ovate [529] instead of
obcordate. This shape is often the most easily recognized and most
striking mark of the variety. In respect to the reproductive organs, the
fertility and abundance of good seed, the _laevifolia_ is by no means
inferior or superior to the original species.
_O. brevistylis_, or the short-styled evening primrose, is the most
curious of all my new forms. It has very short styles, which bring the
stigmas only up to the throat of the calyx tube, instead of upwards of
the anthers. The stigmas themselves are of a different shape, more
flattened and not cylindrical. The pollen falls from the anthers
abundantly on them, and germinates in the ordinary manner.
The ovary which in _lamarckiana_ and in all other new forms is wholly
underneath the calyx-tube, is here only partially so. This tube is
inserted at some distance under its summit. The insertion divides the
ovary into two parts: an upper and a lower one. The upper part is much
reduced in breadth and somewhat attenuated, simulating a prolongation of
the base of the style. The lower part is also reduced, but in another
manner. At the time of flowering it is like the ovary of _lamarckiana_,
neither smaller nor larger. But it is reached by only a very few
pollen-tubes, and is therefore always incompletely fertilized. It does
[530] not fall off after the fading away of the flower, as unfertilized
ovaries usually do; neither does it grow out, nor assume the upright
position of normal capsules. It is checked in its development, and at
the time of ripening it is nearly of the same length as in the
beginning. Many of them contain no good seeds at all; from others I have
succeeded in saving only a hundred seeds from thousands of capsules.
These seeds, if purely pollinated, and with the exclusion of the visits
of insects, reproduce the variety, entirely and without any reversion to
the _lamarckiana_ type.
Correlated with the detailed structures is the form of the flower-buds.
They lack the high stigma placed above the anthers, which in the
_lamarckiana_, by the vigorous growth of the style, extends the calyx
and renders the flower bud thinner and more slender. Those of the
_brevistylis_ are therefore broader and more swollen. It is quite easy
to distinguish the individuals by this striking character alone,
although it differs from the parent in other particulars.
The leaves of the _O. brevistylis_ are more rounded at the tip, but the
difference is only pronounced at times, slightly in the adult rosettes,
but more clearly on the growing summits of the stems and branches. By
this character, the plants [531] may be discerned among the others, some
weeks before the flowers begin to show themselves. But the character by
which the plants may be most easily recognized from a distance in the
field is the failure of the fruits. They were found there nearly every
year in varying, but always small numbers.
Leaving the short-styled primrose, we come now to the last of our group
of retrograde varieties. This is the _O. nanella_, or the dwarf, and is
a most attractive little plant. It is very short of stature, reaching
often a height of only 20-30 cm., or less than one-fourth of that of the
parent. It commences flowering at a height of 10-15 cm., while the
parent-form often measures nearly a meter at this stage of its
development. Being so very dwarfed the large flowers are all the more
striking. They are hardly inferior to those of the _lamarckiana_, and
agree with them in structure. When they fade away the spike is rapidly
lengthened, and often becomes much longer than the lower or vegetative
part of the stem.
The dwarfs are one of the most common mutations in my garden, and were
observed in the native locality and also grown from seeds saved there.
Once produced they are absolutely constant. I have tried many thousands
of seeds from various dwarf mutants, and never observed [532] any trace
of reversion to the _lamarckiana_ type. I have also cultivated them in
successive generations with the same result. In a former lecture we have
seen that contrary to the general run of horticultural belief, varieties
are as constant as the best species, if kept free from hybrid
admixtures. This is a general rule, and the exceptions, or cases of
atavism are extremely rare. In this respect it is of great interest to
observe that this constancy is not an acquired quality, but is to be
considered as innate, because it is already fully developed at the very
moment when the original mutation takes place.
From its first leaves to the rosette period, and through this to the
lengthening of the stem, the dwarfs are easily distinguished from any
other of their congeners. The most remarkable feature is the shape of
the leaves. They are broader and shorter, and especially at the base
they are broadened in such a way as to become apparently sessile. The
stalk is very brittle, and any rough treatment may cause the leaves to
break off. The young seedlings are recognizable by the shape of the
first two or three leaves, and when more of them are produced, the
rosettes become dense and strikingly different from others. Later leaves
are more nearly like the parent-type, but the petioles remain short. The
bases of the blades are frequently [533] almost cordate, the laminae
themselves varying from oblong-ovate to ovate in outline. The stems are
often quite unbranched, or branched only at the base of the spike.
Strong secondary stems are a striking attribute of the _lamarckiana_
parent, but they are lacking, or almost so in the dwarfs. The stem is
straight and short, and this, combined with the large crown of bright
flowers, makes the dwarfs eminently suitable for bed or border plants.
Unfortunately they are very sensitive, especially to wet weather.
_Oenothera gigas_ and _O. rubrinervis_, or the giant, and the red-veined
evening-primroses, are the names given to two robust and stout species,
which seem to be equal in vigor to the parent-plant, while diverging
from it in striking characters. Both are true elementary species,
differentiated from _lamarckiana_ in nearly all their organs and
qualities, but not showing any preponderating character of a retrograde
nature. Their differences may be compared with those of the elementary
species of other genera, as for instance, of _Draba_, or of violets, as
will be seen by their description.
The giant evening-primrose, though not taller in stature than _O.
lamarckiana_, deserves its name because it is so much stouter in all
respects. [534] The stems are robust, often with twice the diameter of
_lamarckiana_ throughout. The internodes are shorter, and the leaves
more numerous, covering the stems with a denser foliage. This shortness
of the internodes extends itself to the spike, and for this reason the
flowers and fruits grow closer together than on the parent-plant. Hence
the crown of bright flowers, opening each evening, is more dense and
more strikingly brilliant, so much the more so as the individual flowers
are markedly larger than those of the parents. In connection with these
characters, the flower-buds are seen to be much stouter than those of
_lamarckiana_. The fruits attain only half the normal size, but are
broader and contain fewer, but larger seeds.
The _rubrinervis_ is in many respects a counterpart to the _gigasv, but
its stature is more slender. The spikes and flowers are those of the
_lamarckianav, but the bracts are narrower. Red veins and red streaks on
the fruits afford a striking differentiating mark, though they are not
absolutely lacking in the parent-species. A red hue may be seen on the
calyx, and even the yellow color of the petals is somewhat deepened in
the same way. Young plants are often marked by the pale red tinge of the
mid-veins, but in adult rosettes, or from lack of sunshine, this hue is
often very faint.
[535] The leaves are narrow, and a curious feature of this species is
the great brittleness of the leaves and stems, especially in annual
individuals, especially in those that make their stem and flowers in the
first year. High turgidity and weak development of the mechanical and
supporting tissues are the anatomical cause of this deficiency, the
bast-fibers showing thinner walls than those of the parent-type under
the microscope. Young stems of _rubrinervis_ may be broken off by a
sharp stroke, and show a smooth rupture across all the tissues, while
those of _lamarckiana_ are very tough and strong.
Both the giant and the red-veined species are easily recognized in the
rosette-stage. Even the very young seedlings of the latter are clearly
differentiated from the _lamarckiana_, but often a dozen leaves are
required, before the difference may be seen. Under such circumstances
the young plants must reach an age of about two months before it is
possible to discern their characters, or at least before these
characters have become reliable enough to enable us to judge of each
individual without doubt. But the divergencies rapidly become greater.
The leaves of _O. gigas_ are broader, of a deeper green, the blade more
sharply set off against the stalk, all the rosettes [536] becoming stout
and crowded with leaves. Those of _O. rubrinervis_ on the contrary are
thin, of a paler green and with a silvery white surface; the blades are
elliptic, often being only 2 cm. or less in width. They are acute at the
apex and gradually narrowed into the petiole.
It is quite evident that such pale narrow leaves must produce smaller
quantities of organic food than the darker green and broad organs of the
_gigas_. Perhaps this fact is accountable partly, at least, for the more
robust growth of the giant in the second year. Perhaps also some
relation exists between this difference in chemical activity and the
tendency to become annual or biennial. The _gigas_, as a rule, produces
far more, and the _rubrinervis_ far less biennial plants than the
_lamarckiana_. Annual culture for the one is as unreliable as biennial
culture for the other. _Rubrinervis_ may be annual in apparently all
specimens, in sunny seasons, but _gigas_ will ordinarily remain in the
state of rosettes during the entire first summer. It would be very
interesting to obtain a fuller insight into the relation of the length
of life to other qualities, but as yet the facts can only be detailed as
they stand.
Both of these stout species have been found [537] quite constant from
the very first moment of their appearance. I have cultivated them from
seed in large numbers, and they have never reverted to the
_lamarckiana_. From this they have inherited the mutability or the
capacity of producing at their turn new mutants. But they seem to have
done so incompletely, changing in the direction of more absolute
constancy. This was especially observed in the case of _rubrinervis_,
which is not of such rare occurrence as _O. gigas_, and which it has
been possible to study in large numbers of individuals. So for instance,
the "red-veins" have never produced any dwarfs, notwithstanding they are
produced very often by the parent-type. And in crossing experiments also
the red-veins gave proof of the absence of a mutative capacity for their
production.
Leaving the robust novelties, we may now take up a couple of forms,
which are equally constants and differentiated from the parent species
in exactly the same manner, though by other characters, but which are so
obviously weak as to have no manifest chance of self maintenance in the
wild state. These are the whitish and the oblong-leaved
evening-primroses or the _Oenothera albida_ and _oblonga_.
_Oenothera albida_ is a very weak species, with whitish, narrow leaves,
which are evidently incapable [538] of producing sufficient quantities
of organic food. The young seedling-plants are soon seen to lag behind,
and if no care is taken of them they are overgrown by their neighbors.
It is necessary to take them out, to transplant them into pots with
richly manured soil, and to give them all the care that should be given
to weak and sickly plants. If this is done fully grown rosettes may be
produced, which are strong enough to keep through the winter. In this
case the individual leaves become stronger and broader, with oblong
blades and long stalks, but retain their characteristic whitish color.
In the second year the stems become relatively stout. Not that they
become equal to those of _lamarckiana_, but they become taller than
might have been expected from the weakness of the plants in the previous
stages. The flowers and racemes are nearly as large as those of the
parent-form, the fruits only a little thinner and containing a smaller
quantity of seed. From these seeds I have grown a second and a third
generation, and observed that the plants remain true to their type.
_O. oblonga_ may be grown either as an annual, or as a biennial. In the
first case it is very slender and weak, bearing only small fruits and
few seeds. In the alternative case however, it [539] becomes densely
branched, bearing flowers on quite a number of racemes and yielding a
full harvest of seeds. But it always remains a small plant, reaching
about half the height of that of _lamarckiana_.
When very young it has broader leaves, but in the adult rosettes the
leaves become very narrow, but fleshy and of a bright green color. They
are so crowded as to leave no space between them unoccupied. The
flowering spikes of the second year bear long leaf-like bracts under the
first few flowers, but those arising later are much shorter. Numerous
little capsules cover the axis of the spike after the fading away of the
petals, constituting a very striking differentiating mark. This species
also was found to be quite constant, if grown from pure seed.
We have now given the descriptions of seven new forms, which diverge in
different ways from the parent-type. All were absolutely constant from
seed. Hundreds or thousands of seedlings may have arisen, but they
always come true and never revert to the original _O. lamarckiana_ type.
From this they have inherited the condition of mutability, either
completely or partly, and according to this they may be able to produce
new forms themselves. But this occurs only rarely, and combinations of
more than one [540] type in one single plant seem to be limited to the
admixture of the dwarf stature with the characters of the other new
species.
These seven novelties do not comprise the whole range of the new
productions of my _O. lamarckiana_. But they are the most interesting
ones. Others, as the _O. semilata_ and the _O. leptocarpa_ are quite as
constant and quite as distinct, but have no special claims for a closer
description. Others again were sterile, or too weak to reach the adult
stage and to yield seeds, and no reliable description or appreciation
can be given on the ground of the appearance of a single individual.
Contrasted with these groups of constant forms are three inconstant
types which we now take up. They belong to two different groups,
according to the cause of their inconstancy. In one species which I call
_O. lata_, the question of stability or instability must remain wholly
unsolved, as only pistillate flowers are produced, and no seed can be
fertilized save by the use of the pollen of another form, and therefore
by hybridization. The other head comprises two fertile forms, _O.
scintillans_ and _O. elliptica_, which may easily be fertilized with
their own pollen, but which gave a progeny only partly similar to the
parents.
The _Oenothera lata_ is a very distinct form [541] which was found more
than once in the field, and recently (1902) in a luxuriant flowering
specimen. It has likewise been raised from seeds collected in different
years at the original station. It is also wholly pistillate. Apparently
the anthers are robust, but they are dry, wrinkled and nearly devoid of
contents. The inner wall of cells around the groups of pollen grow out
instead of being resorbed, partly filling the cavity which is left free
by the miscarriage of the pollen-grains. This miscarriage does not
affect all the grains in the same degree, and under the microscope a few
of them with an apparently normal structure may be seen. But the
contents are not normally developed, and I have tried in vain to obtain
fertilization with a large number of flowers. Only by
cross-fertilization does _O. lata_ produce seeds, and then as freely as
the other species when self-fertilized. Of course its chance of ever
founding a wild type is precluded by this defect.
_O. lata_ is a low plant, with a limp stem, bent tips and branches, all
very brittle, but with dense foliage and luxuriant growth. It has bright
yellow flowers and thick flower-buds. But for an unknown reason the
petals are apt to unfold only partially and to remain wrinkled
throughout the flowering time. The stigmas are slightly divergent from
the normal type, [542] also being partly united with one another, and
laterally with the summit of the style, but without detriment to their
function.
Young seedlings of _lata_ may be recognized by the very first leaves.
They have a nearly orbicular shape and are very sharply set off against
their stalk. The surface is very uneven, with convexities and
concavities on both sides. This difference is lessened in the later
leaves, but remains visible throughout the whole life of the plant, even
during the flowering season. Broad, sinuate leaves with rounded tips are
a sure mark of _O. lata_. On the summits of the stems and branches they
are crowded so as to form rosettes.
Concerning inheritance of these characteristics nothing can be directly
asserted because of the lack of pollen. The new type can only be
perpetuated by crosses, either with the parent form or some other
mutant. I have fertilized it, as a rule, with _lamarckiana_ pollen, but
have often also used that from _nanella_ and others. In doing so, the
_lata_ repeats its character in part of its offspring. This part seems
to be independent of the nature of the pollen used, but is very variable
according to external circumstances. On the average one-fourth of the
offspring become _lata_, the others assuming the type of the
pollen-parent, if this was a _lamarckiana_ or [543] partly this type and
partly that of any other of the new species derived from _lamarckiana_,
that might have been used as the pollen-parent. This average seems to be
a general rule, recurring in all experiments, and remaining unchanged
through a long series of successive generations. The fluctuations around
this mean go up to nearly 50% and down nearly to 1%, but, as in other
cases, such extreme deviations from the average are met with only
exceptionally.
The second category includes the inconstant but perfectly fertile
species. I have already given the names of the only two forms, which
deserve to be mentioned here.
One of them is called _scintillans_ or the shiny evening-primrose,
because its leaves are of a deep green color with smooth surfaces,
glistening in the sunshine. On the young rosettes these leaves are
somewhat broader, and afterwards somewhat narrower than those of _O.
lamarckiana_ at the corresponding ages. The plants themselves always
remain small, never reaching the stature of the ancestral type. They are
likewise much less branched. They can easily be cultivated in annual
generations, but then do not become as fully developed and as fertile,
as when flowering in the second year. The flowers have the same
structure as those of the _lamarckiana_, but are of a smaller size.
[544] Fertilizing the flowers artificially with their own pollen,
excluding the visiting insects by means of paper bags, and saving and
sowing the seed of each individual separately, furnishes all the
requisites for the estimation of the degree of stability of this
species. In the first few weeks the seed-pans do not show any
unequality, and often the young plants must be replanted at wider
intervals, before anything can be made out with certainty. But as soon
as the rosettes begin to fill it becomes manifest that some of them are
more backward than others in size. Soon the smaller ones show their
deeper green and broader leaves, and thereby display the attributes of
the _scintillans_. The other grow faster and stronger and exhibit all
the characteristics of ordinary _lamarckiana_s.
The numerical proportion of these two groups has been found different on
different occasions. Some plants give about one-third _scintillans_ and
two-thirds _lamarckiana_, while the progeny of individuals of another
strain show exactly the reverse proportion.
Two points deserve to be noticed. First the progeny of the _scintillans_
appears to be mutable in a large degree, exceeding even the
_lamarckiana_. The same forms that are produced most often by the
parent-family are also most ordinarily [545] met with among the
offspring of the shiny evening-primrose. They are _oblonga_, _lata_ and
_nanella_. _Oblonga_ was observed at times to constitute as much as 1%
or more of the sowings of _scintillans_, while _lata_ and _nanella_ were
commonly seen only in a few scattering individuals, although seldom
lacking in experiments of a sufficient size.
Secondly the instability seems to be a constant quality, although the
words themselves are at first sight, contradictory. I mean to convey the
conception that the degree of instability remains unchanged during
successive generations. This is a very curious fact, and strongly
reminds us of the hereditary conditions of striped-flower varieties.
But, on the contrary, the atavists, which are here the individuals with
the stature and the characteristics of the _lamarckiana_, have become
_lamarckiana_s in their hereditary qualities, too. If their seed is
saved and sown, their progeny does not contain any _scintillans_, or at
least no more than might arise by ordinary mutations.
One other inconstant new species is to be noted, but as it was very rare
both in the field and in my cultures, and as it was difficult of
cultivation, little can as yet be said about it. It is the _Oenothera
elliptica_, with narrow elliptical leaves and also with elliptical
petals. It repeats [546] its type only in a very small proportion of its
seed.
All in all we thus have a group of a dozen new types, springing from an
original form in one restricted locality, and seen to grow there, or
arising in the garden from seeds collected from the original locality.
Without any doubt the germs of the new types are fully developed within
the seed, ready to be evolved at the time of germination. More favorable
conditions in the field would no doubt allow all of the described new
species to unfold their attributes there, and to come into competition
with each other and with the common parents. But obviously this is only
of secondary importance, and has no influence on the fact that a number
of new types, analogous to the older swarms of _Draba_, _Viola_ and of
many other polymorphous species, have been seen to arise directly in the
wild state.
[547]