ed by nature, this
is the result of injurious influences which make themselves felt later
on. This is because incompatibilities may be present in too closely
related idioplasms and these are sources of weakness in unrestricted
development. The more complicated is the idioplasm, the oftener this
occurs, whereas absolute lack of crossing is not detrimental to the
simplest (asexual) organisms.

11. ACTION OF EXTERNAL INFLUENCES.[E]

The environment provides the organism above all with force and matter
for its life processes. It causes no permanent variation and has only an
ontogenetic significance, if the limits of the idioplasmic elasticity
are not exceeded; it maintains the growth and metabolic assimilation of
the individual, and conditions individual (not hereditary) differences,
which constitute "nutrition varieties." (See page 30.) These appear as
the direct results of operating causes.

[E] In order to explain adaptations Naegeli assumes that external
influences, if acting at the same point in a given manner for a
long time, may induce slight adaptive variations which are
perpetuated and increased. On the important subject of
adaptation in general Naegeli is almost diametrically opposed to
Darwin and Weismann. Naegeli assigns to the principle of utility
a very limited sphere; Weismann regards adaptation as
all-powerful. According to Naegeli, the organic world would have
become much what it is, if natural selection and adaptation had
performed no part in the operations of nature. He aptly says,
that natural selection prunes the phylogenetic tree, but does
not cause new branches to grow. He allows that the principle of
selection is well suited to explain the adaptation of organisms
to their environment and the suitableness and physiological
peculiarities of their structure, but he asserts that in the
definiteness of variation of plants and in their progressive
differentiation there is evidence of a higher and controlling
perfecting principle.--_Trans._

When the stress of environment exceeds the limits of idioplasmic
elasticity, its influence brings about permanent variations, which are
imperceptibly small, it is true, in the single individual, but which,
when the stimulus is active for a long period of time in the same
manner, increase to perceptible magnitude. These variations are
inheritable in the phylogenetic sense and contribute to the