50 Scientific. Memoirs by
flowers is conferred on a set of females which, by reason of certain peculiarities
in their structure, are incapable of receiving advantage from the companionship,
and these pseudo-females produce insects: while the structurally perfect females
are shut up in receptacles from which males are excluded, and to which their
pollen cannot to all appearance get access; and yet these perfectly formed
females produce fertile seeds.
The problem to which I have to invite attention is therefore this—How are
the females in the second set of receptacles fertilized? And, as a contribution
towards the solution of this problem, I have only a few facts to offer, and these
are as follows. From a very early stage, the gall flowers are seen to differ from
the fertile female flowers in having shorter, stouter, more terminal styles, which
are never hairy, and which are crowned by dilated false stigmas. When fully
developed, many of the galls are recognisable at a glance by the presence
inside them of the pupa of an insect which can be seen through the coats
of the false achene into which the ovary develops. But whether the pupa
be visible or not, or whether it be present or not, the false achene of the gall
flower is distinguishable from the true achene of the fertilized ovary of the
perfect female flower by being more globular in shape, and by its outer coat
being quite smooth and tense. These peculiarities in the style and stigma are
not the consequences of the deposit of the egg of an insect in the ovary. On
the other hand, it has been suggested that these are original peculiarities which
may account for the selection of these flowers by the insect as a breeding
ground. In another respect also the galls differ from the fertile female
flowers. The pedicels of the latter are from the first thin and form delicate
stalks to the comparatively large ovoid ovaries. The pedicel of the gall flower
is, on the other hand, at first thick, and the ovary occupies a small excavation
near its apex; but, as the ovarian cavity swells with the development of the
pupa inside it, the pedicel gradually becomes thinner, until, by the time the pupa
is ready to escape, the pedicel of the gall has become as thin as that of the
fertile female flower.
If one of the gall-bearing receptacles be cut open at rather an early stage
of its history, a number of small pellucid maggots* (Plate X, Fig. 8) may be
observed crawling about over the apices of the closely-packed gall flowers. At
this time these gall flowers have their pedicels thick, their ovarial cavities are
small and contain no pupæ. The male flowers are yet small and their perianths
are firmly closed, and, as they lie just under the lower scales that close the
ostiole of the fig, these flowers almost escape observation until searched for.
If a gall-bearing receptacle of slightly maturer age be cut open, the ovarian
cavities of the galls will be found to be tense and swollen, and either to be
empty, or to contain the pupa of an insect; the pedicels have become compara-
tively thin; and the male flowers have increased in size, but are still closed.
If a still more mature receptacle be cut open, the male flowers will be
found to be fully expanded, and the anthers to be shedding their pollen;
* These maggots are not, however, to be found in every receptacle bearing male and gall flowers.