XV 
The Botanical Work of Darwin. 
temper of the tool he has forged, or who can hope to see his 
single arm multiply a thousandfold, and a great guild of 
craftsmen working with his aims and his methods. Yet this 
is what has happened, for the great mass of biological or 
natural history work of the last thirty years is part of that 
harvest of which the Fertilization of Orchids was the first- 
fruits. What Mr. Huxley has said is true here : — c Even 
a cursory glance at the history of the biological sciences 
during the last quarter of a century is sufficient to justify the 
assertion, that the most potent instrument for the extension 
of the realm of natural knowledge which has come into 
men’s hands since the publication of Newton’s Principia is 
Darwin’s Origin of Species 1 .’ 
But it is not possible to judge the Orchid book until 
Darwin’s researches on Cross and Self Fertilization, published 
in 1876, are taken into account. 
In the Orchid book he showed that certain machinery 
exists for insuring cross-fertilization. In Cross and Self 
Fertilization he showed, for the first time, the definitely 
measurable effect of cross-fertilization, and thus expressed in 
figures the value of the selective force at work in modifying 
the floral mechanism. And in Cross and Self Fertilization 
he generalized the position one degree further^ by showing 
that the value of crossing does not depend on the union of 
two individuals as representatives of different sexes, but as 
representatives of different conditions of life. The light in 
this way thrown on the meaning of sexual reproduction is, in 
my judgement, one of his greatest achievements in science. 
A great deal of work, part only of which has been published, 
was done on the floral mechanism of the Papilionaceae , on 
Leschenaultia , on Melastomaceae , and on Clarkia. In the two 
last-named examples it was the possession of two different 
sets of anthers which interested him, a state of things which 
has been shown in some cases to be a case of division of 
labour, one set supplying pollen as an attraction, while the 
remainder serve as fertilizers. The Melastomaceae are a good 
1 Life and Letters, Vol. ii, p. 204. 
