e great botanist, Naegeli, has propounded a most ingenious and
elaborate theory of evolution, as dependent mainly on inherent
initial tendency. We can notice only one or two of its salient
points. All development is, according to his view, due to a tendency
in the primitive living substance toward more complete division of
labor and greater complexity. This tendency, which he calls
progression, or the tendency toward perfection, is the result of the
chemical and molecular structure of the formative controlling
protoplasm (idioplasm) of the body, and is transmitted with other
parental traits from generation to generation. And structural
complexity thus increases like money at compound interest.
Development is a process of unfolding or of realization of the
possibilities of this tendency under the stimulus of surrounding
influences. Environment plays an essential part in his system. But
only such changes are transmissible to future generations as have
resulted from modifications arising in the idioplasm. Descendants of
plants which have varied under changed conditions revert, as a rule,
to the old type, when returned to the old surroundings. And in the
animal world effects of use and disuse are, according to his view,
not transmissible.

Natural selection plays a very subordinate part. It is purely
destructive. Given an infinity of place and nourishment--do away,
that is, with all struggle and selection--and the living world would
have advanced, purely by the force of the progressive tendency, just
as far as it now has; only there would have survived an indefinite
number of intermediate forms. It would have differed from our
present living world as the milky way does from the starry
firmament.

He compares the plant kingdom to a great, luxurious tree, branching
from its very base, whose twigs would represent the present stage of
our different species. Left to itself it would put out a chaos of
innumerable branches. Natural selection, like a gardener, prunes the
tree into shape. Children might imagine that the gardener caused the
growth; but the tree would have been broader and have branched more
luxuriantly if left to itself.[A]

[Footnote A: See Naegeli, "Theorie der Abstammungslehre," p. 18;
also pp. 12, 118, 285.]

Every species must vary perpetually. Now this proposition is
apparently not in accord with fact; for some have remained unchanged
during immense periods. And natural selection, by removing the less