xiv The Botanical Work of Darwin. 
there was, by an unformulated arrangement, a certain com- 
munity of research on many subjects. For instance, on 
orchid-fertilization, self-sterility, heterostylism, and climbing 
plants the facts supplied by Muller were important con- 
tributions to the building up and extending of Darwin’s 
theories. 
It is needless to say more on the Variation of Animals and 
Plants, the book is in the hands of every one, and is familiar 
to botanists. I regret that space forbids me to quote the 
true and forcible description of the effect of the book on 
botanists and horticulturists, given by Sir W. Thiselton-Dyer 
in his classical essay on the Botanical Work of Darwin 1 . 
Second or Physiological Period. 
The work of this period, though distinguishable in a certain 
sense from the purely evolutionary work, is yet bound to it 
by many interwoven ties. Thus, the Orchid book (taken in 
conjunction with Cross and Self-Fertilization) is the amplifica- 
tion of a passage in the first edition of the Origin 2 . ‘The 
flowers of two distinct individuals of the same species would 
thus get crossed ; and the act of crossing, we have good reason 
to believe (as will hereafter be more fully alluded to), would 
produce very vigorous seedlings, which consequently would 
have the best chance of flourishing and surviving.’ 
Its connexion, from another point of view, with the evolu- 
tionary work has already been made clear, and I have 
indicated its value as a demonstration of the efficiency of his 
theory of evolution as a guide in natural history work. He 
acknowledged the value of his Orchid work in relation to 
natural selection : — ‘ I can show the meaning of some of the 
apparently meaningless ridges [and] horns ; who will now 
venture to say that this or that structure is useless 3 ? ’ 
It is not every man who can prove so convincingly the 
1 Charles Darwin, Nature Series, 1882, p. 38. 
2 P* 9 2 - 
3 Life and Letters, Vol. iii, p. 254. 
