I have tried to show previously that species, in the ordinary sense of
the word, consist of distinct groups of units. In systematic works these
groups are all designated by the name of varieties, but it is usually
granted that the units of the system are not always of the same value.
Hence we have distinguished between elementary species and varieties
proper. The first are combined into species whose common original type
is now lost or unknown, and from their characters is derived an
hypothetical image of what the common ancestor is supposed to have been.
The varieties proper are derived in most cases from still existing
types, and therefore are subjoined to them. A closer investigation has
shown that this derivation is ordinarily produced by the loss of some
definite attribute, or by the re-acquisition of an apparently [460] lost
character. The elementary species, on the other hand, must have arisen
by the production of new qualities, each new acquisition constituting
the origin of a new elementary form.
Moreover we have seen, that such improvements and such losses constitute
sharp limits between the single unit-forms. Every type, of course,
varies around an average, and the extremes of one form may sometimes
reach or even overlap those of the nearest allies, but the offspring of
the extremes always return to the type. The transgression is only
temporary and a real transition of one form to another does not come
within ordinary features of fluctuating variability. Even in the cases
of eversporting varieties, where two opposite types are united within
one race, and where the succeeding individuals are continually swinging
from one extreme to the other, passing through a wide range of
intermediate steps, the limits of the variety are as sharply defined and
as free from real transgression as in any other form.
In a complete systematic enumeration of the real units of nature, the
elementary species and varieties are thus observed to be discontinuous
and separated by definite gaps. Every unit may have its youth, may lead
a long life in the adult state and may finally die. But through [461]
the whole period of its existence it remains the same, at the end as
sharply defined from its nearest allies as in the beginning. Should some
of the units die out, the gaps between the neighboring ones will become
wider, as must often have been the case. Such segregations, however
important and useful for systematic distinctions, are evidently only of
secondary value, when considering the real nature of the units
themselves.
We may now take up the other side of the problem. The question arises as
to how species and varieties have originated. According to the Darwinian
theory they have been produced from one another, the more highly
differentiated ones from the simpler, in a graduated series from the
most simple forms to the most complicated and most highly organized
existing types. This evolution of course must have been regular and
continuous, diverging from time to time into new directions, and linking
all organisms together into one common pedigree. All lacunae in our
present system are explained by Darwin as due to the extinction of the
forms, which previously filled them.
Since Lamarck first propounded the conception of a common origin for all
living beings, much has been done to clear up our ideas as to the real
nature of this process. The broader [462] aspect of the subject,
including the general pedigree of the animal and vegetable kingdom, may
be said to have been outlined by Darwin and his followers, but this
phase of the subject lies beyond the limits of our present discussion.
The other phase of the problem is concerned with the manner in which the
single elementary species and varieties have sprung from one another.
There is no reason to suppose that the world is reaching the end of its
development, and so we are to infer that the production of new species
and varieties is still going on. In reality, new forms are observed to
originate from time to time, both wild and in cultivation, and such
facts do not leave any doubt as to their origin from other allied types,
and according to natural and general laws.
In the wild state however, and even with cultivated plants of the field
and garden, the conditions, though allowing of the immediate observation
of the origination of new forms, are by no means favorable for a closer
inquiry into the real nature of the process. Therefore I shall postpone
the discussion of the facts till another lecture, as their bearing will
be more easily understood after having dealt with more complete cases.
These can only be obtained by direct experimentation. Comparative
studies, of course, [463] are valuable for the elucidation of general
problems and broad features of the whole pedigree, but the narrower and
more practical question as to the genetic relation of the single forms
to one another must be studied in another way, by direct experiment. The
exact methods of the laboratory must be used, and in this case the
garden is the laboratory. The cultures must be guarded with the
strictest care and every precaution taken to exclude opportunities for
error. The parents and grandparents and their offspring must be kept
pure and under control, and all facts bearing upon the birth or origin
of the new types should be carefully recorded.
Two great difficulties have of late stood in the way of such
experimental investigation. One of them is of a theoretical, the, other
of a practical nature. One is the general belief in the supposed
slowness of the process, the other is the choice of adequate material
for experimental purposes. Darwin's hypothesis of natural selection as
the means by which new types arise, is now being generally interpreted
as stating the slow transformation of ordinary fluctuating divergencies
from the average type into specific differences. But in doing so it is
overlooked that Quetelet's law of fluctuating variability was not yet
discovered at the time, when Darwin propounded his theory. So there
[464] is no real and intimate connection between these two great
conceptions. Darwin frequently pointed out that a long period of time
might be needed for slow improvements, and was also a condition for the
occurrence of rare sports. In any case those writers have been in error,
according to my opinion, who have refrained from experimental work on
the origin of species, on account of this narrow interpretation of
Darwin's views. The choice of the material is quite another question,
and obviously all depends upon this choice. Promising instances must be
sought for, but as a rule the best way is to test as many plants as
possible. Many of them may show nothing of interest, but some might lead
to the desired end.
For to-day's lecture I have chosen an instance, in which the grounds
upon which the choice was based are very evident. It is the origin of
the peloric toad-flax (_Linaria vulgaris peloria_).
The ground for this choice lies simply in the fact that the peloric
toad-flax is known to have originated from the ordinary type at
different times and in different countries, under more or less divergent
conditions. It had arisen from time to time, and hence I presumed that
there was a chance to see it arise again. If this should happen under
experimental circumstances [465] the desired evidence might easily be
gathered. Or, to put it in other words, we must try to arrange things so
as to be present at the time when nature produces another of these rare
changes.
There was still another reason for choosing this plant for observational
work. The step from the ordinary toad-flax to the peloric form is short,
and it appears as if it might be produced by slow conversion. The
ordinary species produces from time to time stray peloric flowers. These
occur at the base of the raceme, or rarely in the midst of it. In other
species they are often seen at the summit. Terminal pelories are usually
regular, having five equal spurs. Lateral pelories are generally of
zygomorphic structure, though of course in a less degree than the normal
bilabiate flowers, but they have unequal spurs, the middle one being of
the ordinary length, the two neighboring being shorter, and those
standing next to the opposite side of the flower being the shortest of
all. This curious remainder of the original, symmetrical structure of
the flower seems to have been overlooked hitherto by the investigators
of peloric toad-flaxes.
The peloric variety of this plant is characterized by its producing only
peloric flowers. No single bilabiate or one-spurred flower remains.
[466] I once had a lot of nearly a hundred specimens of this fine
variety, and it was a most curious and beautiful sight to observe the
many thousands of nearly regular flowers blooming at the same time. Some
degree of variability was of course present, even in a large measure.
The number of the spurs varied between four and six, transgressing these
limits in some instances, but never so far as to produce really
one-spurred flowers. Comparing this variety with the ordinary type, two
ways of passing over from the one to the other might be imagined. One
would entail a slow increase of the number of the peloric flowers on
each plant, combined with a decrease of the number of the normal ones,
the other a sudden leap from one extreme to the other without any
intermediate steps. The latter might easily be overlooked in field
observations and their failure may not have the value of direct proof.
They could never be overlooked, on the other hand, in experimental
culture.
The first record of the peloric toad-flax is that of Zioberg, a student
of Linnaeus, who found it in the neighborhood of Upsala. This curious
discovery was described by Rudberg in his dissertation in the year 1744.
Soon afterwards other localities were discovered by Link near Gottingen
in Germany about 1791 and afterwards [467] in the vicinity of Berlin, as
stated by Ratzeburg, 1825. Many other localities have since been
indicated for it in Europe, and in my own country some have been noted
of late, as for instance near Zandvoort in 1874 and near Oldenzaal in
1896. In both these last named cases the peloric form arose
spontaneously in places which had often been visited by botanists before
the recorded appearance, and therefore, without any doubt, they must
have been produced directly and independently by the ordinary species
which grows in the locality. The same holds good for other occurrences
of it. In many instances the variety has been recorded to disappear
after a certain lapse of time, the original specimens dying out and no
new ones being produced. _Linaria_ is a perennial herb, multiplying
itself easily by buds growing on the roots, but even with this means of
propagation its duration seems to have definite limits.
There is one other important point arguing strongly for the independent
appearance of the peloric form in its several localities. It is the
difficulty of fertilization and the high degree of sterility, even if
artificially pollinated. Bees and bumble-bees are unable to crawl into
the narrow tubular flowers, and to bring the fertilizing pollen to the
stigma. Ripe capsules with seeds [468] have never been seen in the wild
state. The only writer who succeeded in sowing seeds of the peloric
variety was Wildenow and he got only very few seedlings. But even in
artificial pollination the result is the same, the anthers seeming to be
seriously affected by the change. I tried both self-fertilization and
cross-pollination, and only with utmost care did I succeed in saving
barely a hundred seeds. In order to obtain them I was compelled to
operate on more than a thousand flowers on about a dozen peloric plants.
The variety being wholly barren in nature, the assumption that the
plants in the different recorded localities might have a common origin
is at once excluded. There must have been at least nearly as many
mutations as localities. This strengthens the hope of seeing such a
mutation happen in one's own garden. It should also be remembered that
peloric flowers are known to have originated in quite a number of
different species of _Linaria_, and also with many of the allied species
within the range of the Labiatiflorae.
I will now give the description of my own experiment. Of course this did
not give the expected result in the first year. On the contrary, it was
only after eight years' work that I had the good fortune of observing
the mutation. [469] But as the whole life-history of the preceding
generations had been carefully observed and recorded, the exact
interpretation of the fact was readily made.
My culture commenced in the year 1886. I chose some plants of the normal
type with one or two peloric flowers besides the bilabiate majority
which I found on a locality in the neighborhood of Hilversum in Holland.
I planted the roots in my garden and from them had the first flowering
generation in the following summer. From their seeds I grew the second
generation in three following years. They flowered profusely and
produced in 1889 only one, and in 1890 only two peloric structures. I
saved the seeds in 1889 and had in 1890-1891 the third generation. These
plants likewise flowered only in the second year, and gave among some
thousands of symmetrical blossoms, only one five-spurred flower. I
pollinated this flower myself, and it produced abundant fruit with
enough seeds for the entire culture in 1892, and they only were sown.
Until this year my generations required two years each, owing to the
perennial habit of the plants. In this way the prospects of the culture
began to decrease, and I proposed to try to heighten my chances by
having a new generation yearly. With this intention I sowed the [470]
selected seeds in a pan in the glasshouse of my laboratory and planted
them out as soon as the young stems had reached a length of some few
centimeters. Each seedling was put in a separate pot, in heavily manured
soil. The pots were kept under glass until the beginning of June, and
the young plants produced during this period a number of secondary stems
from the curious hypocotylous buds which are so characteristic of the
species. These stems grew rapidly and as soon as they were strong
enough, the plants were put into the beds. They all, at least nearly
all, some twenty specimens, flowered in the following month.
I observed only one peloric flower among the large number present. I
took the plant bearing this flower and one more for the culture of the
following year, and destroyed all others. These two plants grew on the
same spot, and were allowed to fertilize each other by the agency of the
bees, but were kept isolated from any other congener. They flowered
abundantly, but produced only one-spurred bilabiate flowers during the
whole summer. They matured more than 10 cu. cm. of seeds.
It is from this pair of plants that my peloric race has sprung. And as
they are the ancestors of the first closely observed case of peloric
mutation, [471] it seems worth while to give some details regarding
their fertilization.
Isolated plants of _Linaria vulgaris_ do not produce seed, even if
freely pollinated by bees. Pollen from other plants is required. This
requirement is not at all restricted to the genus _Linaria_, as many
instances are known to occur in different families. It is generally
assumed that the pollen of any other individual of the same species is
capable of producing fertilization, although it is to be said that a
critical examination has been made in but few instances.
This, however, is not the case, at least not in the present instance. I
have pollinated a number of plants, grown from seed of the same strain
and combined them in pairs, and excluded the visits of insects, and
pollen other than that of the plant itself and that of the specimen with
which it was paired. The result was that some pairs were fertile and
others barren. Counting these two groups of pairs, I found them nearly
equal in number, indicating thereby that for any given individual the
pollen of half of the others is potent, but that of the other half
impotent. From these facts we may conclude the presence of a curious
case of dimorphy, analogous to that proposed for the primroses, but
without visible differentiating marks in the flowers. At least such
opposite characters [472] have as yet not been ascertained in the case
of our toad-flax.
In order to save seed from isolated plants it is necessary, for this
reason, to have at least two individuals, and these must belong to the
two physiologically different types. Now in the year 1892, as in other
years, my plants, though separated at the outset by distances of about
20 cm. from each other, threw out roots of far greater length, growing
in such a way as to abolish the strict isolation of the individuals. Any
plot may produce several stems from such roots, and it is manifestly
impossible to decide whether they all belong to one original plant or to
the mixed roots of several individuals. No other strains were grown on
the same bed with my plants however, and so I considered all the stems
of the little group as belonging to one plant. But their perfect
fertility showed, according to the experience described, that there must
have been at least two specimens mingled together.
Returning now to the seeds of this pair of plants, I had, of course, not
the least occasion to ascribe to it any higher value than the harvest of
former years. The consequence was that I had no reason to make large
sowings, and grew only enough young plants to have about 50 in bloom in
the summer of 1894. Among [473] these, stray peloric flowers were
observed in somewhat larger number than in the previous generations, 11
plants bearing one or two, or even three such abnormalities. This
however, could not be considered as a real advance, since such plants
may occur in varying, though ordinarily small numbers in every
generation.
Besides them a single plant was seen to bear only peloric flowers; it
produced racemes on several stems and their branches. All were peloric
without exception. I kept it through the winter, taking care to preserve
a complete isolation of its roots. The other plants were wholly
destroyed. Such annihilation must include both the stems and roots and
the latter of course requires considerable labor. The following year,
however, gave proof of the success of the operation, since my plant
bloomed luxuriously for the second time and remained true to the type of
the first year, producing peloric flowers exclusively.
Here we have the first experimental mutation of a normal into a peloric
race. Two facts were clear and simple. The ancestry was known for over a
period of four generations, living under the ordinary care and
conditions of an experimental garden, isolated from other toad-flaxes,
but freely fertilized by bees or at times by myself. This ancestry was
quite constant as to [474] the peloric peculiarity, remaining true to
the wild type as it occurs everywhere in my country, and showing in no
respect any tendency to the production of a new variety.
The mutation took place at once. It was a sudden leap from the normal
plants with very rare peloric flowers to a type exclusively peloric. No
intermediate steps were observed. The parents themselves had borne
thousands of flowers during two summers, and these were inspected nearly
every day, in the hope of finding some pelories and of saving their seed
separately. Only one such flower was seen. If there had been more, say a
few in every hundred flowers, it might be allowable to consider them as
previous stages, showing a preparation of the impending change. But
nothing of this kind was observed. There was simply no visible
preparation for the sudden leap.
This leap, on the other hand, was full and complete. No reminiscence of
the former condition remained. Not a single flower on the mutated plant
reverted to the previous type. All were thoroughly affected by the new
attribute, and showed the abnormally augmented number of spurs, the
tubular structure of the corolla and the round and narrow entrance of
its throat. The whole plant departed absolutely from the old type of its
progenitors.
[475] Three ways were open to continue my experiment. The first was
indicated by the abundant harvest from the parent-plants of the
mutation. It seemed possible to compare the numerical proportion of the
mutated seeds with those of normal plants. In order to ascertain this
proportion I sowed the greatest part of my 10 cu. cm. of seed and
planted some 2,000 young plants in little pots with well-manured soil. I
got some 1,750 flowering plants and observed among them 16 wholly
peloric individuals. The numerical proportion of the mutation was
therefore in this instance to be calculated equal to about 1% of the
whole crop.
This figure is of some importance. For it shows that the chance of
finding mutations requires the cultivation of large groups of
individuals. One plant in each hundred may mutate, and cultures of less
than a hundred specimens must therefore be entirely dependent on chance
for the appearance of new forms, even if such should accidentally have
been produced and lay dormant in the seed. In other cases mutations may
be more numerous, or on the contrary, more rare. But the chance of
mutative changes in larger numbers is manifestly much reduced by this
experiment, and they may be expected to form a very small proportion of
the culture.
[476] The second question which arose from the above result was this.
Could the mutation be repeated? Was it to be ascribed to some latent
cause which might be operative more than once? Was there some hidden
tendency to mutation, which, ordinarily weak, was strengthened in my
cultures by some unknown influence? Was the observed mutation to be
explained by a common cause with the other cases recorded by
field-observations? To answer this question I had only to continue my
experiment, excluding the mutated individuals from any intercrossing
with their brethren. To this end I saved the seeds from duly isolated
groups in different years and sowed them at different times. For various
causes I was not prepared to have large cultures from these seeds, but
notwithstanding this, the mutation repeated itself. In one instance I
obtained two, in another, one peloric plant with exclusively
many-spurred flowers. As is easily understood, these were related as
"nieces" to the first observed mutants. They originated in quite the
same way, by a sudden leap, without any preparation and without any
intermediate steps.
Mutation is proved by this experience to be of an iterative nature. It
is the expression of some concealed condition, or as it is generally
[477] called, of some hidden tendency. The real nature of this state of
the hereditary qualities is as yet wholly unknown. It would not be safe
to formulate further conclusions before the evidence offered by the
evening-primroses is considered.
Thirdly, the question arises, whether the mutation is complete, not only
as to the morphologic character, but also as to the hereditary
constitution of the mutated individuals. But here unfortunately the high
degree of sterility of the peloric plants, as previously noted, makes
the experimental evidence a thing of great difficulty. During the course
of several years I isolated and planted together the peloric individuals
already mentioned, all in all some twenty plants. Each individual was
nearly absolutely sterile when treated with its own pollen, and the aid
of insects was of no avail. I intercrossed my plants artificially, and
pollinated more than a thousand flowers. Not a single one gave a normal
fruit, but some small and nearly rudimentary capsules were produced,
bearing a few seeds. From these I had 119 flowering plants, out of which
106 were peloric and 13 one-spurred. The great majority, some 90%, were
thus shown to be true to their new type. Whether the 10% reverting ones
were truly atavists, or whether they were [478] only vicinists, caused
by stray pollen grains from another culture, cannot of course be decided
with sufficient certitude.
Here I might refer to the observations concerning the invisible
dimorphous state of the flowers of the normal toad-flax. Individuals of
the same type, when fertilized with each other, are nearly, but not
absolutely, sterile. The yield of seeds of my peloric plants agrees
fairly well with the harvest which I have obtained from some of the
nearly sterile pairs of individuals in my former trial. Hence the
suggestion is forced upon us that perhaps, owing to some unknown cause,
all the peloric individuals of my experiment belonged to one and the
same type, and were sterile for this reason only. If this is true, then
it is to be presumed that all previous investigators have met the same
condition, each having at hand only one of the two required types. And
this discussion has the further advantage of showing the way, in which
perhaps a full and constant race of peloric toad-flaxes may be obtained.
Two individuals of different type are required to start from. They seem
as yet never to have arisen from one group of mutations. But if it were
possible to combine the products of two mutations obtained in different
countries and under different conditions, there would be a chance [479]
that they might belong to the supposed opposite types, and thus be
fertile with one another. My peloric plants are still available, and the
occurrence of this form elsewhere would give material for a successful
experiment. The probability thereof is enhanced by the experience that
my peloric plants bear large capsules and a rich harvest of seeds when
fertilized from plants of the normal one-spurred race, while they remain
nearly wholly barren by artificial fertilization with others. I suppose
that they are infertile with the normal toad-flaxes of their own sexual
disposition, but fertile with those of the opposite constitution. At all
events the fact that they may bear abundant seed when properly
pollinated is an indication of successful experiments on the possibility
of gaining a hereditary race with exclusively peloric flowers. And such
a race would be a distinct gain for sundry physiologic inquiries, and
perhaps not wholly destitute of value from an horticultural point of
view.
Returning now to the often recorded occurrence of peloric toad-flaxes in
the wild state and recalling our discussion about the improbability of a
dispersion from one locality to another by seed, and the probability of
independent origin for most of these cases, we are confronted with the
conception that a latent [480] tendency to mutation must be universally
present in the whole species. Another observation, although it is of a
negative character, gains in importance from this point of view. I refer
to the total lack of intermediate steps between normal and peloric
individuals. If such links had ordinarily been produced previous to the
purely peloric state they would no doubt have been observed from time to
time. This is so much the more probable as _Linaria_ is a perennial
herb, and the ancestors of a mutation might still be in a flowering
condition together with their divergent offspring. But no such
intermediates are on record. The peloric toad-flaxes are, as a rule,
found surrounded by the normal type, but without intergrading forms.
This discontinuity has already been insisted upon by Hofmeister and
others, even at the time when the theory of descent was most under
discussion, and any link would surely have been produced as a proof of a
slow and continuous change. But no such proof has been found, and the
conclusion seems admissible that the mutation of toad-flaxes ordinarily,
if not universally, takes place by a sudden step. Our experiment may
simply be considered as a thoroughly controlled instance of an often
recurring phenomenon. It teaches us how, in the [481] main, the peloric
mutations must be assumed to proceed.
This conception may still be broadened. We may include in it all similar
occurrences, in allied and other species. There is hardly a limit to the
possibilities which are opened up by this experience. But it will be
well to refrain from hazardous theorizing, and consider only those cases
which may be regarded as exact repetitions of the same phenomenon and of
which our culture is one of the most recent instances on record. We will
limit ourselves to the probable origin of peloric variations at large,
of which little is known, but some evidence may be derived from the
recorded facts. Only one case can be said to be directly analogous to
our observations.
This refers to the peloric race of the common snapdragon, or
_Antirrhinum majus_ of our gardens. It is known to produce peloric races
from time to time in the same way as does the toadflax. But the
snapdragon is self-fertile and so is its peloric variety. Some cases are
relatively old, and some of them have been recorded and in part observed
by Darwin. Whence they have sprung and in what manner they were
produced, seems never to have been noted. Others are of later origin,
and among these one or two varieties have been accidentally produced
[482] in the nursery of Mr. Chr. Lorenz in Erfurt, and are now for sale,
the seeds being guaranteed to yield a large proportion of peloric
individuals. The peloric form in this case appeared at once, but was not
isolated, and was left free to visiting insects, which of course crossed
it with the surrounding varieties. Without doubt the existence of two
color-varieties of the peloric type, one of a very dark red, indicating
the "Black prince" variety as the pollen-parent, and the other with a
white tube of the corolla, recalling the form known as "Delila," is due
to these crossings. I had last year (1903) a large lot of plants, partly
normal and partly peloric, but evidently of hybrid origin, from seeds
from this nursery, showing moreover all intermediate steps between
nearly wholly peloric individuals and apparently normal ones. I have
saved the seeds of the isolated types and before seeing the flowers of
their offspring, nothing can be said about the purity and constancy of
the type, when freed from hybrid admixtures. The peloric snapdragon has
five small unequal spurs at the base of its long tube, and in this
respect agrees with the peloric toad-flax.
Other pelories are terminal and quite regular, and occur in some species
of _Linaria_, where I observed them in _Linaria dalmatica_. The [483]
terminal flowers of many branches were large and beautifully peloric,
bearing five long and equal spurs. About their origin and inheritance
nothing is known.
A most curious terminal pelory is that of the common foxglove or
_Digitalis purpurea_. As we have seen in a previous lecture, it is an
old variety. It was described and figured for the first time by Vrolik
of Amsterdam, and the original specimens of his plates are still to be
seen in the collections of the botanic garden of that university. Since
his time it has been propagated by seed as a commercial variety, and may
be easily obtained. The terminal flower of the central stem and those of
the branches only are affected, all other flowers being wholly normal.
Almost always it is accompanied by other deviations, among which a
marked increase of the number of the parts of the corolla and other
whorls is the most striking. Likewise supernumerary petals on the outer
side of the corolla, and a production of a bud in the center of the
capsule may be often met with. This bud as a rule grows out after the
fading away of the flower, bursting through the green carpels of the
unripe fruit, and producing ordinarily a secondary raceme of flowers.
This raceme is a weak but exact repetition of the first, bearing
symmetrical foxgloves all [484] along and terminating in a peloric
structure. On the branches these anomalies are more or less reduced,
according to the strength of the branch, and conforming to the rule of
periodicity, given in our lecture on the "five-leaved" clover. Through
all this diminution the peloric type remains unchanged and therefore
becomes so much the purer, the weaker the branches on which it stands.
I am not sure whether such peloric flowers have ever been purely
pollinated and their seed saved separately, but I have often observed
that the race comes pure from the seed of the zygomorphic flowers. It is
as yet doubtful whether it is a half race or a double race, and whether
it might be purified and strengthened by artificial selection. Perhaps
the determination of the hereditary percentage described when dealing
with the tricotyls might give the clue to the acquisition of a higher
specialized race. The variety is old and widely disseminated, but must
be subjected to quite a number of additional experiments before it can
be said to be sufficiently understood.
The most widespread peloric variety is that of _Gloxinia_. It has erect
instead of drooping flowers; and with the changed position the structure
is also changed. Like other pelories it has five equal stamens instead
of four unequal [485] ones, and a corolla with five equal segments
instead of an upper and a lower lip. It shows the peloric condition in
all of its flowers and is often combined with a small increase of the
number of the parts of the whorls. It is for sale under the name of
_erecta_, and may be had in a wide range of color-types. It seems to be
quite constant from seed.
Many other instances of peloric flowers are on record. Indian cress or
_Tropaeolum majus_ loses the spur in some double varieties and with it
most of its symmetrical structure; it seems to be considered justly as a
peloric malformation. Other species produce such anomalies only from
time to time and nothing is known about their hereditary tendency. One
of the most curious instances is the terminal flower of the raceme of
the common laburnum, which loses its whole papilionaceous character and
becomes as regularly quinate as a common buttercup.
Some families are more liable to pelorism than others. Obviously all the
groups, the flowers of which are not symmetrical, are to be excluded.
But then we find that labiates and their allies among the dicotyledonous
plants, and orchids among the monocotyledonous ones are especially
subjected to this alteration. In both groups many genera and a long list
of species [486] could be quoted as proof. The family of the labiates
seems to be essentially rich in terminal pelories, as for instance in
the wild sage or _Salvia_ and the dead-nettle or _Lamium_. Here the
pelories have long and straight corolla-tubes, which are terminated by a
whorl of four or five segments. Such forms often occur in the wild state
and seem to have a geographic distribution as narrowly circumscribed as
in the case of many small species. Those of the labiates chiefly belong
to southern Europe and are unknown at least in some parts of the other
countries. On the contrary terminal pelories of _Scrophularia nodosa_
are met with from time to time in Holland. Such facts clearly point to a
common origin, and as only the terminal flowers are affected by the
malformation, the fertility of the whole plant is evidently not
seriously infringed upon.
Before leaving the labiates, we may cite a curious instance of pelorism
in the toad-flax, which is quite different from the ordinary peloric
variety. This latter may be considered from a morphologic standpoint to
be owing to a five-fold repetition of the middle part of the underlip.
This conception would at once explain the occurrence of five spurs and
of the orange border all around the corolla-tube. We might readily
imagine that any other of the five [487] parts of the corolla could be
repeated five-fold, in which case there would be no spur, and no orange
hue on the upper corolla-ring. Such forms really occur, though they seem
to be more rare than the five-spurred pelories. Very little is known
about their frequency and hereditary qualities.
Orchids include a large number of peloric monstrosities and moreover a
wild pelory which is systematically described not only as a separate
species but even as a new genus. It bears the name of _Uropedium
lindenii_, and is so closely related to _Cypripedium caudatum_ that many
authors take it for the peloric variety of this plant. It occurs in the
wild state in some parts of Mexico, where the _Cypripedium_ also grows.
Its claims to be a separate genus are lessened by the somewhat monstrous
condition of the sexual organs, which are described as quite abnormal.
But here also, intermediates are lacking, and this fact points to a
sudden origin.
Many cases of pelorism afford promising material for further studies of
experimental mutations. The peloric toad-flax is only the prototype of
what may be expected in other cases. No opportunity should be lost to
increase the as yet too scanty, evidence on this point.
[488]