ards assumed a greater importance 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." (Ibid. page 437.) 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" (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"
(page 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 too strongly expressed.") is, however, a
pregnant expression of the fact that cross-fertilisation is exceedingly
widespread and has been shown in the majority of cases to be beneficial,
and that in those plants in which we find self-pollination regularly
occurring cross-pollination may occasionally take place.

An attempt has been made to express in brief the main results of
Darwin's work on the biology of flowers. We have seen that his object
was to elucidate important general questions, particularly the question
of the significance of sexual reproduction.

It remains to consider what influence his work has had on botanical
science. That this influence has been very considerable, is shown by
a glance at the literature on the biology of flowers published since
Darwin wrote. Before the book on orchids was published there was nothing
but the old and almost forgotten works of Kolreuter and Sprengel with
the exception of a few scattered references. Darwin's investigations
gave the first stimulus to the development of an extensive literature on
floral biology. In Knuth's "Handbuch der Blutenbiologie" ("Handbook
of Flower Pollination", Oxford, 1906) as many as 3792 papers on this
subject are enu