es appear
together not only in the same region, but even at the same points, while
the geographical distribution of the more marked varieties and of
related species offers no conclusion as to their origin, but only as to
the last great migration of the plant world, because they arose before
this period, as indeed appears from their distribution.

Just as different varieties arise simultaneously from one kinship at the
same place, the same variety may arise in places far separated, when the
analogous external exciting causes occasion an identical transformation
in the idioplasm. The experimental proof lies in the fact that like
beginnings of varieties often appear at great distances from each other.

An apparent social origin of varieties is indicated, when, after having
come together in migration, they first develop the unlike determinants
which they have gained in various locations. An apparently individual
origin of the same or different varieties is indicated, when the
formation of the determinants take place at one and the same place, but
their development follows only after the kindred has been scattered by
migration.

19. GENERAL RELATION OF THE PHYLOGENETIC LINES IN THE ORGANIC KINGDOMS.

Since the nature of an organism is contained in the sum of its
idioplasmic determinants alone, the evolution of a phylogeny consists in
the evolution of the idioplasm. This is perceived from the succession
of the visible ontogenetic characteristics which in general run parallel
with it. The idioplasm varies in two ways: (1) by an _automatic
perfecting process_; (2) by _adaptation to environment_.

By virtue of the _automatic variation_ of the idioplasm the ontogenies
of a phylogenetic line attain to a continually more complex organization
and greater differentiation of function. In this differentiation,
however, only the qualitative differences are of importance;
quantitative and numerical gradations may be disregarded. The more
complex admits of more combinations than the simpler; hence if a
phylogeny reaches a higher stage by automatic evolution it may branch
into several lines, of which each appears as the continuation of the
parent stock.

Since _adaptive variations_ depend only on the transmutations of
environment, an organism may rise to a higher organization and division
of labor by continually adapting itself to the changed environment. But
the organism may also change its adaptation while it remains at the same