Medical Officers of the Army of India.
41
for determination is whether any special evolution of gas takes place during
periods of flowering in excess of that evolved at other times. Experiments of
various kinds (vide note B) agree in indicating that no special evolution occurs.
In the first place it can be shown that in plants from which all the leaves have
been. carefully removed hardly any evolution of gas manifests itself through the
flower. In the second place it appears that the amount of gaseous evolution from
the flower varies in direct proportion to the number and size of healthy leaves on
the plant. Finally, it is demonstrable that, allowing for this, the total gaseous
evolution from both the flowers and general surfaces of flowering plants closely
corresponds in amount with that from the general surfaces alone of non-flowering
ones.
Such a peculiar phenomenon might on a priori grounds lead to a belief that
it was connected with some important end in the life history of the plant, and
on examining the subject more closely from this point of view, it becomes evident
that this is actually the case.
The great end which is attained by the large liberation of gas from the
floral organs is that fertilisation is securely carried out in the submerged flowers
which come to maturity while far beneath the surface of the water. The majo-
rity of the strongest plants of Ottelia grow in such deep water that none of their
flowers have a chance of ever reaching the surface, and, even in plants growing
in shallower water, very many flowers remain permanently submerged. Were no
special provision at hand a very large proportion of flowers, and all those of the
most vigorous plants, would fail to produce any seed, as the pollen grains are
affected by contact with water in the ordinary fashion, swelling up, bursting, and
discharging their contents without germinating.
Owing, however, to the constant evolution of gases taking place in the dif-
ferent parts of the flower at the period of maturation of the essential organs, these
are kept continuously free from contact with the surrounding water, and germin-
ation of the pollen grains and penetration of the stigmatic tissues are accordingly
permitted to proceed without any obstacle.
The flowers of Ottelia, whether aerial or subaqueous, are essentially de-
veloped so as to secure self-fertilisation. The anthers and stigmas mature
simultaneously and at a period when the flower is still in bud. The filaments and
styles are in close apposition and are arranged alternately, and the anthers are
closely applied to the stigmas in such a fashion that, as a rule, each of the anther
lobes is on opening in direct relation to one of the stigmatic lobes of a separate
stigma connected with a separate style.
The precise arrangement and relations of the anthers and stigmas varies
naturally to some extent in different instances (vide Note B), but in any case the
relation is one of direct apposition, and the pollen, on dehiscence of the anther
lobes, is directly applied to the stigmatic surfaces in large quantities. The pollen
grains, moreover, germinate at a very early period, many of them beginning to do
so whilst still within the anther lobes and apart from contact with the stigmas.