mily, the Gesneraceae has left single
representatives from the Pyrenees to the Balkans; and in the former
a diminutive yam still lingers. These are only illustrations of the
evidence which constantly accumulates and which finds no rational
explanation except that which Darwin has given to it.

The theory of southward migration is the key to the interpretation of
the geographical distribution of plants. It derived enormous support
from the researches of Heer and has now become an accepted commonplace.
Saporta in 1888 described the vegetable kingdom as "emigrant pour suivre
une direction determinee et marcher du nord au sud, a la recherche
de regions et de stations plus favorables, mieux appropriees aux
adaptations acquises, a meme que la temperature terrestre perd ses
conditions premieres." ("Origine Paleontologique des arbres", Paris,
1888, page 28.) If, as is so often the case, the theory now seems to be
a priori inevitable, the historian of science will not omit to record
that the first germ sprang from the brain of Darwin.

In attempting this sketch of Darwin's influence on Geographical
Distribution, I have found it impossible to treat it from an external
point of view. His interest in it was unflagging; all I could say became
necessarily a record of that interest and could not be detached from it.
He was in more or less intimate touch with everyone who was working
at it. In reading the letters we move amongst great names. With an
extraordinary charm of persuasive correspondence he was constantly
suggesting, criticising and stimulating. It is hardly an exaggeration
to say that from the quiet of his study at Down he was founding and
directing a wide-world school.

POSTSCRIPTUM.

Since this essay was put in type Dr Ernst's striking account of the "New
Flora of the Volcanic Island of Krakatau" (Cambridge, 1909.) has reached
me. All botanists must feel a debt of gratitude to Prof. Seward for
his admirable translation of a memoir which in its original form
is practically unprocurable and to the liberality of the Cambridge
University Press for its publication. In the preceding pages I have
traced the laborious research by which the methods of Plant Dispersal
were established by Darwin. In the island of Krakatau nature has
supplied a crucial experiment which, if it had occurred earlier, would
have at once secured conviction of their efficiency. A quarter of a
century ago every trace of organic life in the island was "de