yet sufficiently exact to demonstrate
the frequently small quantitative differences in chemical composition.
Questions relating to the enzymes, which are of the greatest importance
in all these life-processes, are especially complicated. In any case
it is the necessary result of such an hypothesis that we must employ
chemical methods of investigation in dealing with problems connected
with the physiology of form.

II. INFLUENCE OF ENVIRONMENT ON THE TRANSFORMATION OF SPECIES.

The study of the physiology of form-development in a pure species has
already yielded results and makes slow but sure progress. The physiology
of the possibility of the transformation of one species into another is
based, as yet, rather on pious hope than on accomplished fact. From
the first it appeared to be hopeless to investigate physiologically
the origin of Linnean species and at the same time that of the natural
system, an aim which Darwin had before him in his enduring work. The
historical sequence of events, of which an organism is the expression,
can only be treated hypothetically with the help of facts supplied
by comparative morphology, the history of development, geographical
distribution, and palaeontology. (See Lotsy, "Vorlesungen" (Jena, I.
1906, II. 1908), for summary of the facts.) A glance at the controversy
which is going on today in regard to different hypotheses shows that
the same material may lead different investigators to form entirely
different opinions. Our ultimate aim is to find a solution of the
problem as to the cause of the origin of species. Indeed such
attempts are now being made: they are justified by the fact that under
cultivation new and permanent strains are produced; the fundamental
importance of this was first grasped by Darwin. New points of view in
regard to these lines of inquiry have been adopted by H. de Vries
who has succeeded in obtaining from Oenothera Lamarckiana a number of
constant "elementary" species. Even if it is demonstrated that he was
simply dealing with the complex splitting up of a hybrid (Bateson,
"Reports to the Evolution Committee of the Royal Society", London, 1902;
cf. also Lotsy, "Vorlesungen", Vol. I. page 234.), the facts adduced in
no sense lose their very great value.

We must look at the problem in its simplest form; we find it in every
case where a new race differs essentially from the original type in a
single character only; for example, in the colour of the flowers or in