The Different Forms of Flowers on Plants of the Same Species | Page 8

to hermaphrodite species which
bear differently constructed flowers; but there are some plants that
produce differently formed seeds, of which Dr. Kuhn has given a list.
(Introduction/15. 'Botanische Zeitung' 1867 page 67.) With the
Umbelliferae and Compositae, the flowers that produce these seeds
likewise differ, and the differences in the structure of the seeds are of a
very important nature. The causes which have led to differences in the
seeds on the same plant are not known; and it is very doubtful whether
they subserve any special end.
We now come to our second Class, that of monoecious species, or

those which have their sexes separated but borne on the same plant.
The flowers necessarily differ, but when those of one sex include
rudiments of the other sex, the difference between the two kinds is
usually not great. When the difference is great, as we see in
catkin-bearing plants, this depends largely on many of the species in
this, as well as in the next or dioecious class, being fertilised by the aid
of the wind; for the male flowers have in this case to produce a
surprising amount of incoherent pollen. (Introduction/16. Delpino
'Studi sopra uno Lignaggio Anemofilo' Firenze 1871.) Some few
monoecious plants consist of two bodies of individuals, with their
flowers differing in function, though not in structure; for certain
individuals mature their pollen before the female flowers on the same
plant are ready for fertilisation, and are called proterandrous; whilst
conversely other individuals, called proterogynous, have their stigmas
mature before their pollen is ready. The purpose of this curious
functional difference obviously is to favour the cross-fertilisation of
distinct plants. A case of this kind was first observed by Delpino in the
Walnut (Juglans regia), and has since been observed with the common
Nut (Corylus avellana). I may add that according to H. Muller the
individuals of some few hermaphrodite plants differ in a like manner;
some being proterandrous and others proterogynous. (Introduction/17.
Delpino 'Ult. Osservazioni sulla Dicogamia' part 2 fasc 2 page 337. Mr.
Wetterhan and H. Muller on Corylus 'Nature' volume 11 page 507 and
1875 page 26. On proterandrous and proterogynous hermaphrodite
individuals of the same species, see H. Muller 'Die Befruchtung' etc.
pages 285, 339.) On cultivated trees of the Walnut and Mulberry, the
male flowers have been observed to abort on certain individuals, which
have thus been converted into females; but whether there are any
species in a state of nature which co-exist as monoecious and female
individuals, I do not know. (Introduction/18. 'Gardener's Chronicle'
1847 pages 541, 558.)
The third Class consists of dioecious species, and the remarks made
under the last class with respect to the amount of difference between
the male and female flowers are here applicable. It is at present an
inexplicable fact that with some dioecious plants, of which the
Restiaceae of Australia and the Cape of Good Hope offer the most

striking instance, the differentiation of the sexes has affected the whole
plant to such an extent (as I hear from Mr. Thiselton Dyer) that Mr.
Bentham and Professor Oliver have often found it impossible to match
the male and female specimens of the same species. In my seventh
chapter some observations will be given on the gradual conversion of
heterostyled and of ordinary hermaphrodite plants into dioecious or
sub-dioecious species.
The fourth and last Class consists of the plants which were called
polygamous by Linnaeus; but it appears to me that it would be
convenient to confine this term to the species which coexist as
hermaphrodites, males and females; and to give new names to several
other combinations of the sexes--a plan which I shall here follow.
Polygamous plants, in this confined sense of the term, may be divided
into two sub-groups, according as the three sexual forms are found on
the same individual or on distinct individuals. Of this latter or trioicous
sub-group, the common Ash (Fraxinus excelsior) offers a good instance:
thus, I examined during the spring and autumn fifteen trees growing in
the same field; and of these, eight produced male flowers alone, and in
the autumn not a single seed; four produced only female flowers, which
set an abundance of seeds; three were hermaphrodites, which had a
different aspect from the other trees whilst in flower, and two of them
produced nearly as many seeds as the female trees, whilst the third
produced none, so that it was in function a male. The separation of the
sexes, however, is not complete in the Ash; for the female flowers
include stamens, which drop off at an early period, and their anthers,
which never open or dehisce, generally contain pulpy matter instead of
pollen. On some female trees, however, I found a few anthers
containing pollen grains apparently sound. On the male trees most