The Different Forms of Flowers on Plants of the Same Species | Page 6

in the ground; but some few other
plants behave in the same manner; and, as they do not bury all their
flowers, they might have formed a small separate subdivision.
Another interesting subdivision consists of certain plants, discovered
by H. Muller, some individuals of which bear conspicuous flowers
adapted for cross- fertilisation by the aid of insects, and others much
smaller and less conspicuous flowers, which have often been slightly
modified so as to ensure self-fertilisation. Lysimachia vulgaris,
Euphrasia officinalis, Rhinanthus crista-galli, and Viola tricolor come
under this head. (Introduction/4. H. Muller 'Nature' September 25, 1873
volume 8 page 433 and November 20, 1873 volume 9 page 44. Also
'Die Befruchtung der Blumen' etc. 1873 page 294.) The smaller and
less conspicuous flowers are not closed, but as far as the purpose which
they serve is concerned, namely, the assured propagation of the species,

they approach in nature cleistogamic flowers; but they differ from them
by the two kinds being produced on distinct plants.
With many plants, the flowers towards the outside of the inflorescence
are much larger and more conspicuous than the central ones. As I shall
not have occasion to refer to plants of this kind in the following
chapters, I will here give a few details respecting them. It is familiar to
every one that the ray-florets of the Compositae often differ remarkably
from the others; and so it is with the outer flowers of many
Umbelliferae, some Cruciferae and a few other families. Several
species of Hydrangea and Viburnum offer striking instances of the
same fact. The Rubiaceous genus Mussaenda presents a very curious
appearance from some of the flowers having the tip of one of the sepals
developed into a large petal-like expansion, coloured either white or
purple. The outer flowers in several Acanthaceous genera are large and
conspicuous but sterile; the next in order are smaller, open, moderately
fertile and capable of cross-fertilisation; whilst the central ones are
cleistogamic, being still smaller, closed and highly fertile; so that here
the inflorescence consists of three kinds of flowers. (Introduction/5. J.
Scott 'Journal of Botany' London new series volume 1 1872 pages
161-164.) From what we know in other cases of the use of the corolla,
coloured bracteae, etc., and from what H. Muller has observed on the
frequency of the visits of insects to the flower-heads of the
Umbelliferae and Compositae being largely determined by their
conspicuousness, there can be no doubt that the increased size of the
corolla of the outer flowers, the inner ones being in all the above cases
small, serves to attract insects. (Introduction/6. 'Die Befruchtung der
Blumen' pages 108, 412.) The result is that cross-fertilisation is thus
favoured. Most flowers wither soon after being fertilised, but
Hildebrand states that the ray-florets of the Compositae last for a long
time, until all those on the disc are impregnated; and this clearly shows
the use of the former. (Introduction/7. See his interesting memoir
'Ueber die Geschlechtsverhaltniss bei den Compositen' 1869 page 92.)
The ray-florets, however, are of service in another and very different
manner, namely, by folding inwards at night and during cold rainy
weather, so as to protect the florets of the disc. (Introduction/8. Kerner
clearly shows that this is the case: 'Die Schutzmittel des Pollens' 1873

page 28.) Moreover they often contain matter which is excessively
poisonous to insects, as may be seen in the use of flea- powder, and in
the case of Pyrethrum, M. Belhomme has shown that the ray-florets are
more poisonous than the disc-florets in the ratio of about three to two.
We may therefore believe that the ray-florets are useful in protecting
the flowers from being gnawed by insects. (Introduction/9. 'Gardener's
Chronicle' 1861 page 1067. Lindley 'Vegetable Kingdom' on
Chrysanthemum 1853 page 706. Kerner in his interesting essay 'Die
Schutzmittel der Bluthen gegen unberufene Gaste' 1875 page 19, insists
that the petals of most plants contain matter which is offensive to
insects, so that they are seldom gnawed, and thus the organs of
fructification are protected. My grandfather in 1790 'Loves of the
Plants' canto 3 note to lines 184, 188, remarks that "The flowers or
petals of plants are perhaps in general more acrid than their leaves;
hence they are much seldomer eaten by insects.")
It is a well-known yet remarkable fact that the circumferential flowers
of many of the foregoing plants have both their male and female
reproductive organs aborted, as with the Hydrangea, Viburnum and
certain Compositae; or the male organs alone are aborted, as in many
Compositae. Between the sexless, female and hermaphrodite states of
these latter flowers, the finest gradations may be traced, as Hildebrand
has shown. (Introduction/10. 'Ueber die Geschlechtsverhaltnisse bei
den Compositen' 1869 pages 78-91.) He also shows that there is a close
relation between the size of the corolla