in the full development of
the seed, but in the vigour of the plant produced from such seed. We see
something of the same kind in certain cases of parthenogenesis, that is,
when the male element is wholly excluded; for M. Jourdan[885] found that,
out of about 58,000 eggs laid by unimpregnated silk-moths, many passed
through their early embryonic stages, showing that they were capable of
self-development, but only twenty-nine out of the whole number produced
caterpillars. Therefore it is not an improbable view that deficient bulk or
quantity in the formative matter, contained within the sexual elements, is
the main cause of their not having the capacity of prolonged separate
existence and development. The belief that it is the function of the
spermatozoa to communicate life to the ovule seems a strange one, seeing
that the unimpregnated ovule is already alive and continues for a
considerable time alive. We shall hereafter see that it is probable that
the sexual elements, or possibly only the female element, include certain
primordial cells, that is, such as have undergone no differentiation, and
which are not present in an active state in buds.

_Graft-hybrids._--When discussing in the eleventh chapter the curious case
of the _Cytisus adami_, facts were given which render it to a certain
degree probable, in accordance with the belief of some distinguished
botanists, that, when the tissues of two plants {365} belonging to distinct
species or varieties are intimately united, buds are afterwards
occasionally produced which, like hybrids, combine the characters of the
two united forms. It is certain that when trees with variegated leaves are
grafted or budded on a common stock, the latter sometimes produces buds
bearing variegated leaves; but this may perhaps be looked at as a case of
inoculated disease. Should it ever be proved that hybridised buds can be
formed by the union of two distinct vegetative tissues, the essential
identity of sexual and asexual reproduction would be shown in the most
interesting manner; for the power of combining in the offspring the
characters of both parents, is the most striking of all the functions of
sexual generation.

_Direct Action of the Male Element on the Female._--In the chapter just
referred to, I have given abundant proofs that foreign pollen occasionally
affects the mother-plant in a direct manner. Thus, when Gallesio fertilised
an orange-flower with pollen from the lemon, the frui