Ce) 
is an incidental rather than a selected quality. The result of 
his work on heterostyled plants is of importance as showing 
that sterility is no test of specific distinctness, and that it 
depends on differentiation of the sexual elements which is 
independent of any racial difference.” * 
The different forms of a heterostyled plant are adapted for 
cross-fertilisation by insects, and each individual of each form 
is by the same means excluded more or less completely from 
fertilisation by another of the same form. In the former case 
the sexual cells and the accessory apparatus have been kept 
by selection during long generations of syngamy in a high 
state of mutual compatibility ; in the latter asyngamy, partial 
or complete, has produced a large measure of the sterility 
which is its inevitable even if long-delayed result. 
This argument has, I admit, carried me much further than 
I originally intended, and it will be a pleasure to me if the 
following criticism can be overthrown. 
If the special adaptation of heterostyled plants for particu- 
lar lines of syngamy has incidentally resulted in lessened 
fertility, when the unions discouraged by these adaptations 
are artificially secured, and in this case without appeal to the 
physiologically injurious effects of self-fertilisation, why should 
we not similarly explain these effects whenever manifest in 
the self-bred + offspring of any plant especially adapted for 
cross-fertilisation 1 
Darwin tells us in the Autobiography that as soon as his 
“attention was thoroughly aroused to the remarkable fact 
that seedlings of self-fertilised parentage are inferior, even 
in the first generation, in height and vigour to seedlings of 
cross-fertilised parentage,” {| he entered upon a series of 
experiments which lasted eleven years, appearing in 1876 as 
“‘ Effects of Cross and Self-Fertilisation in the Vegetable 
Kingdom.” Of this work he wrote in 1881, “the results 
there arrived at explain, as I believe, the endless and wonder- 
ful contrivances for the transportal of pollen from one plant 
to another of the same species.”§ It is here suggested that 
* «Life and Letters,” vol. iii, p. 296. 
+ See Francis Darwin on ‘‘The Knight Darwin Law,” Nature, October 
27, 1898, p. 630. 
t ‘*Life and Letters,” vol. i, p. 96. § Ibid., vol. i, p. 97. 
