The Different Forms of Flowers on Plants of the Same Species | Page 5

Condition in the Species of Primula, and on their
remarkable Sexual Relations" 'Journal of the Proceedings of the
Linnean Society' volume 6 1862 page 77. "On the Existence of Two
Forms, and on their Reciprocal Sexual Relation, in several Species of
the Genus Linum" Ibid volume 7 1863 page 69. "On the Sexual
Relations of the Three Forms of Lythrum salicaria" Ibid volume 8 1864
page 169. "On the Character and Hybrid-like Nature of the Offspring
from the Illegitimate Unions of Dimorphic and Trimorphic Plants" Ibid
volume 10 1868 page 393. "On the Specific Differences between
Primula veris, Brit. Fl. (var. officinalis, Linn.), P. vulgaris, Brit. Fl. (var.
acaulis, Linn.), and P. elatior, Jacq.; and on the Hybrid Nature of the
Common oxlip. With Supplementary Remarks on Naturally Produced
Hybrids in the Genus Verbascum" Ibid volume 10 1868 page 437.)

They were called by me dimorphic and trimorphic, but have since been
better named by Hildebrand, heterostyled. (Introduction/2. The term
"heterostyled" does not express all the differences between the forms;
but this is a failure common in many cases. As the term has been
adopted by writers in various countries, I am unwilling to change it for
that of heterogone or heterogonous, though this has been proposed by
so high an authority as Professor Asa Gray: see the 'American
Naturalist' January 1877 page 42.) As I have many still unpublished
observations with respect to these plants, it has seemed to me advisable
to republish my former papers in a connected and corrected form,
together with the new matter. It will be shown that these heterostyled
plants are adapted for reciprocal fertilisation; so that the two or three
forms, though all are hermaphrodites, are related to one another almost
like the males and females of ordinary unisexual animals. I will also
give a full abstract of such observations as have been published since
the appearance of my papers; but only those cases will be noticed, with
respect to which the evidence seems fairly satisfactory. Some plants
have been supposed to be heterostyled merely from their pistils and
stamens varying greatly in length, and I have been myself more than
once thus deceived. With some species the pistil continues growing for
a long time, so that if old and young flowers are compared they might
be thought to be heterostyled. Again, a species tending to become
dioecious, with the stamens reduced in some individuals and with the
pistils in others, often presents a deceptive appearance. Unless it be
proved that one form is fully fertile only when it is fertilised with
pollen from another form, we have not complete evidence that the
species is heterostyled. But when the pistils and stamens differ in
length in two or three sets of individuals, and this is accompanied by a
difference in the size of the pollen-grains or in the state of the stigma,
we may infer with much safety that the species is heterostyled. I have,
however, occasionally trusted to a difference between the two forms in
the length of the pistil alone, or in the length of the stigma together
with its more or less papillose condition; and in one instance
differences of this kind have been proved by trials made on the fertility
of the two forms, to be sufficient evidence.
The second sub-group above referred to consists of hermaphrodite

plants, which bear two kinds of flowers--the one perfect and fully
expanded--the other minute, completely closed, with the petals
rudimentary, often with some of the anthers aborted, and the remaining
ones together with the stigmas much reduced in size; yet these flowers
are perfectly fertile. They have been called by Dr. Kuhn cleistogamic,
and they will be described in the last chapter of this volume.
(Introduction/3. 'Botanische Zeitung' 1867 page 65. Several plants are
known occasionally to produce flowers destitute of a corolla; but they
belong to a different class of cases from cleistogamic flowers. This
deficiency seems to result from the conditions to which the plants have
been subjected, and partakes of the nature of a monstrosity. All the
flowers on the same plant are commonly affected in the same manner.
Such cases, though they have sometimes been ranked as cleistogamic,
do not come within our present scope: see Dr. Maxwell Masters
'Vegetable Teratology' 1869 page 403.) They are manifestly adapted for
self- fertilisation, which is effected at the cost of a wonderfully small
expenditure of pollen; whilst the perfect flowers produced by the same
plant are capable of cross-fertilisation. Certain aquatic species, when
they flower beneath the water, keep their corollas closed, apparently to
protect their pollen; they might therefore be called cleistogamic, but for
reasons assigned in the proper place are not included in the present
sub-group. Several cleistogamic species, as we shall hereafter see, bury
their ovaries or young capsules