cial branch of science. This
occurred in the course of the eighteenth century as the result of the
pioneer work of Hales, Duhamel, Ingenhousz, Senebier and others. In
the nineteenth century, particularly in the second half, physiology
experienced an unprecedented development in that it began to concern
itself with the experimental study of nutrition and growth, and with
the phenomena associated with stimulus and movement; on the other hand,
physiology neglected phenomena connected with the production of form, a
department of knowledge which was the province of morphology, a purely
descriptive science. It was in the middle of the last century that the
growth of comparative morphology and the study of phases of development
reached their highest point.

The forms of plants appeared to be the expression of their inscrutable
inner nature; the stages passed through in the development of the
individual were regarded as the outcome of purely internal and hidden
laws. The feasibility of experimental inquiry seemed therefore remote.
Meanwhile, the recognition of the great importance of such a causal
morphology emerged from the researches of the physiologists of that
time, more especially from those of Hofmeister (Hofmeister, "Allgemeine
Morphologie", Leipzig, 1868, page 579.), and afterwards from the work of
Sachs. (Sachs, "Stoff und Form der Pflanzenorgane", Vol. I. 1880; Vol.
II. 1882. "Gesammelte Abhandlungen uber Pflanzen-Physiologie", II.
Leipzig, 1893.) Hofmeister, in speaking of this line of inquiry,
described it as "the most pressing and immediate aim of the investigator
to discover to what extent external forces acting on the organism are of
importance in determining its form." This advance was the outcome of the
influence of that potent force in biology which was created by Darwin's
"Origin of Species" (1859).

The significance of the splendid conception of the transformation of
species was first recognised and discussed by Lamarck (1809); as an
explanation of transformation he at once seized upon the idea--an
intelligible view--that the external world is the determining factor.
Lamarck (Lamarck, "Philosophie zoologique", pages 223-227. Paris, 1809.)
endeavoured, more especially, to demonstrate from the behaviour
of plants that changes in environment induce change in form which
eventually leads to the production of new species. In the case of
animals, Lamarck adopted the teleological view that alterations in the
envir