Self-fertilisation 419 
species reaches the stigma rather later than that of another species, 
the latter does not effect fertilisation. 
Darwin showed that the fertilising power of the pollen of another 
variety or of another individual is greater than that of the plant’s 
own pollen’. This has been demonstrated in the case of Mimulus 
luteus (for the fixed white-flowering variety) and Jberis wmbellata 
with pollen of another variety, and observations on cultivated 
plants, such as cabbage, horseradish, etc. gave similar results. It is, 
however, especially remarkable that pollen of another individual of 
the same variety may be prepotent over the plant’s own pollen. This 
results from the superiority of plants crossed in this manner over 
self-fertilised plants. “Scarcely any result from my experiments has 
surprised me so much as this of the prepotency of pollen from a 
distinct individual over each plant’s own pollen, as proved by the 
greater constitutional vigour of the crossed seedlings.” Similarly, 
in self-fertile plants the flowers of which have not been deprived 
of the male organs, pollen brought to the stigma by the wind or by 
insects from another plant effects fertilisation, even if the plant’s own 
pollen has reached the stigma somewhat earlier. 
Have the results of his experimental investigations modified the 
point of view from which Darwin entered on his researches, or not? 
In the first place the question is, whether or not the opinion ex- 
pressed in the Orchid book that there is “Something injurious” 
connected with self-fertilisation, has been confirmed. We can, at 
all events, affirm that Darwin adhered in essentials to his original 
position; but self-fertilisation afterwards assumed a greater im- 
portance than it formerly possessed. Darwin emphasised the fact 
that “the difference between the self-fertilised and crossed plants 
raised by me cannot be attributed to the superiority of the crossed, 
but to the inferiority of the self-fertilised seedlings, due to the 
injurious effects of self-fertilisation®”’ But he had no doubt that in 
favourable circumstances self-fertilised plants were able to persist 
for several generations without crossing. An occasional crossing 
appears to be useful but not indispensable in all cases; its sporadic 
occurrence in plants in which self-pollination habitually occurs is 
not excluded. Self-fertilisation is for the most part relatively and 
not absolutely injurious and always better than no fertilisation. 
“Nature abhors perpetual self-fertilisation*” is, however, a pregnant 
1 Cross and Self fertilisation, p. 391. 2 Ibid. p. 397. 3 Ibid. p. 437. 
‘ It is incorrect to say, as a writer has lately said, that the aphorism expressed by 
Darwin in 1859 and 1862, “Nature abhors perpetual self-fertilisation,” is not repeated in 
his later works. The sentence is repeated in Cross and Self fertilisation (p. 8), with the 
addition, ‘‘If the word perpetual had been omitted, the aphorism would have been false. 
As it stands, I believe that it is true, though perhaps rather tog strongly expressed.” 
27—2 
