x OBITUARY 297 
must be advantageous in the struggle for exist- 
ence; and, the more perfect the action of the 
mechanism, the greater the advantage. Thus the 
way lay open for the operation of natural selection 
in gradually perfecting the flower as a fertilisation- 
trap. Analogous reasoning applies to the fertil- 
ising insect. The better its structure is adapted 
to that of the trap, the more will it be able to 
profit by the bait, whether of honey or of pollen, 
to the exclusion of its competitors. Thus, by a 
sort of action and reaction, a two-fold series of 
adaptive modifications will be brought about. 
In 1865, the important bearing of this subject 
on his theory led Darwin to commence a great 
series of laborious and difficult experiments on the 
fertilisation of plants, which occupied him for 
eleven years, and furnished him with the unex- 
pectedly strong evidence in favour of the influence 
of crossing which he published in 1876, under the 
title of “ The Effects of Cross and Self Fertilisation 
‘in the Vegetable Kingdom.” Incidentally, as it 
-were, to this heavy piece of work, he made the 
remarkable series of observations on the different 
arrangements by which crossing is favoured and, 
im many cases, necessitated, which appeared in the 
work on “The Different Forms of Flowers in 
Plants of the same Species” in 1877. 
In the course of the twenty years during which 
Darwin was thus occupied in opening up new 
regions of investigation to the botanist and 
