of the internal correlations,
which, however, are still but dimly understood. Darwin repeatedly laid
great stress on this view, although a definite proof of its correctness
could not be given in his time. Such proof requires the direct
observation of a mutation, and it should be stated here that even
the first observations made in this direction have clearly confirmed
Darwin's ideas. The new evening primroses which have sprung in my garden
from the old form of Oenothera Lamarckiana, and which have evidently
been derived from it, in each case, by a single mutation, do not differ
from their parent species in one character only, but in almost all their
organs and qualities. Oenothera gigas, for example, has stouter stems
and denser foliage; the leaves are larger and broader; its thick
flower-buds produce gigantic flowers, but only small fruits with large
seeds. Correlative changes of this kind are seen in all my new forms,
and they lend support to the view that in the gradual development of
highly adapted structures, analogous correlations may have played a
large part. They easily explain large deviations from an original type,
without requiring the assumption of too many steps.

Monstrosities, as their name implies, are widely different in character
from natural species; they cannot, therefore, be adduced as evidence in
the investigation of the origin of species. There is no doubt that they
may have much in common as regards their manner of origin, and that the
origin of species, once understood, may lead to a better understanding
of the monstrosities. But the reverse is not true, at least not as
regards the main lines of development. Here, it is clear, monstrosities
cannot have played a part of any significance.

Reversions, or atavistic changes, would seem to give a better support
to the theory of descent through modifications. These have been of
paramount importance on many lines of evolution of the animal as well
as of the vegetable kingdom. It is often assumed that monocotyledons are
descended from some lower group of dicotyledons, probably allied to that
which includes the buttercup family. On this view the monocotyledons
must be assumed to have lost the cambium and all its influence on
secondary growth, the differentiation of the flower into calyx and
corolla, the second cotyledon or seed-leaf and several other characters.
Losses of characters such as these may have been the result of abrupt
changes, but this does