there is no good reason for rejecting our present hypothesis on account of
the assumed existence of cell-gemmules a few thousand times more numerous.

The gemmules in each organism must be thoroughly diffused; nor does this
seem improbable considering their minuteness, and the steady circulation of
fluids throughout the body. So it must be with the gemmules of plants, for
with certain kinds even a minute fragment of a leaf will reproduce the
whole. But a difficulty here occurs; it would appear that with plants, and
probably with compound animals, such as corals, the gemmules do not spread
from bud to bud, but only through the tissues developed from each separate
bud. We are led to this conclusion from the stock being rarely affected by
the insertion of a bud or graft from a distinct variety. This non-diffusion
of the gemmules is still more plainly shown in the case of ferns; for Mr.
Bridgman[908] has proved that, when spores (which it should be remembered
are of the nature of buds) are taken from a monstrous part of a frond, and
others from an ordinary part, {380} each reproduces the form of the part
whence derived. But this non-diffusion of the gemmules from bud to bud may
be only apparent, depending, as we shall hereafter see, on the nature of
the first-formed cells in the buds.

The assumed elective affinity of each gemmule for that particular cell
which precedes it in the order of development is supported by many
analogies. In all ordinary cases of sexual reproduction the male and female
elements have a mutual affinity for each other: thus, it is believed that
about ten thousand species of Compositae exist, and there can be no doubt
that if the pollen of all these species could be, simultaneously or
successively, placed on the stigma of any one species, this one would elect
with unerring certainty its own pollen. This elective capacity is all the
more wonderful, as it must have been acquired since the many species of
this great group of plants branched off from a common progenitor. On any
view of the nature of sexual reproduction, the protoplasm contained within
the ovules and within the sperm-cells (or the "spermatic force" of the
latter, if so vague a term be preferred) must act on each other by some law
of special affinity, either during or subsequently to impregnation, so that
corresponding parts alone affect each other; thus, a calf produced from a
short-horned cow by a long-horned bull has its horns and not its