", page 424.)

It most however be pointed out, that such mutations as Zeiller, and to
some extent Arber and Parkin, appear to have in view, bridging the gulf
between different Orders and Classes, bear no relation to any mutations
which have been actually observed, such as the comparatively small
changes, of sub-specific value, described by De Vries in the type-case
of Oenothera Lamarckiana. The results of palaeobotanical research have
undoubtedly tended to fill up gaps in the Natural System of plants--that
many such gaps still persist is not surprising; their presence may well
serve as an incentive to further research but does not, as it seems
to the writer, justify the assumption of changes in the past, wholly
without analogy among living organisms.

As regards the succession of species, there are no greater authorities
than Grand'Eury and Zeiller, and great weight must be attached to their
opinion that the evidence from continuous deposits favours a somewhat
sudden change from one specific form to another. At the same time
it will be well to bear in mind that the subject of the "absence of
numerous intermediate varieties in any single formation" was fully
discussed by Darwin. ("Origin of Species", pages 275-282, and page
312.); the explanation which he gave may go a long way to account for
the facts which recent writers have regarded as favouring the theory of
saltatory mutation.

The rapid sketch given in the present essay can do no more than call
attention to a few salient points, in which the palaeontological records
of plants has an evident bearing on the Darwinian theory. At the present
day the whole subject of palaeobotany is a study in evolution, and
derives its chief inspiration from the ideas of Darwin and Wallace. In
return it contributes something to the verification of their teaching;
the recent progress of the subject, in spite of the immense difficulties
which still remain, has added fresh force to Darwin's statement that
"the great leading facts in palaeontology agree admirably with the
theory of descent with modification through variation and natural
selection." (Ibid. page 313.)

XIII. THE INFLUENCE OF ENVIRONMENT ON THE FORMS OF PLANTS. By Georg
Klebs, PH.D.

Professor of Botany in the University of Heidelberg.

The dependence of plants on their environment became the object of
scientific research when the phenomena of life were first investigated
and physiology took its place as a spe