n a transition from one generation to
the next following, mediated by the idioplasm of the germ cell. In
asexual (monogenic) reproduction there is continuity of the same
idioplasm. Therefore the parent continues in the offspring its specific
life, as the stem continues its specific life in the branch. All the
peculiarities conditioned by the idioplasm remain unchanged in the
offspring. The latter, as the immediate continuation of the preceding
ontogeny, starts from the point at which the germ cell left it, so that
immediately after the germ cell is separated at the close of the
ontogeny or before, the offspring passes at one time rapidly through
the whole ontogeny, at another only the remainder or a part of it (the
latter in alternation of generations and in asexual propagation of
phanerogams).

In sexual (digenic) reproduction the formation of the germ cell is
brought about by the union in equal parts of both parental idioplasms.
The offspring is the organism resulting from the union of the force and
matter of the parents, and represents in its nature the united
continuation of their ontogenies. The characteristics of development of
the child depend however on the viability of the determinants of the
mingled idioplasms in which a new equilibrium has been formed. Hence if
the child bears more resemblance to the father or to the mother, it
follows that some of the inherited determinants develop while the others
remain latent. If the child has certain visible characteristics more
marked than either parent, it becomes possible only by the development
of determinants which had previously been latent. The fact that the
mother furnishes the germ cell with nutritive plasm and that she
nourishes it for a considerable time does not increase the number of
maternal determinants nor their capability of development.

If two corresponding characters, one derived from the father, the other
from the mother, come into conflict in sexual reproduction, the one or
the other, or even a third alternative characteristic, which heretofore
was present as a latent determinant, may develop in the child. But also
both parental characters may appear at once and in various combinations.
Whether the development follows in the one way or the other depends on
the strength of the individual determinants, on the kind of their
idioplasmic arrangement, and on their agreement with the nature of the
newly formed idioplasm.

16. HEREDITY AND VARIATION.