REPRODUCTION 449 
flower’ is frequently somewhat loosely and erroneously 
made use of when pollination is meant. 
We have seen that cross-fertilisation is ag a rule more 
advantageous to a plant than the fusion of gametes which 
are both produced by the same individual. In the same 
way certain advantages are secured by the process of cross- 
pollination or the application of the pollen of one flower to 
the stigma of a different one of the same species. In the 
case of flowering plants or any others which are hetero- 
sporous, self-fertilisation in the strict sense is of course 
impossible, as the male and female cells which fuse together 
are necessarily borne upon gametophytes which originate 
from different spores and cannot thus be derived imme- 
diately from the same individual. Self-pollination, or the 
transference of pollen from the stamens to the stigma of 
the same flower, is, however, possible, and in many cases 
occurs in the ordinary course of events. Cross-pollination, 
or the bringing together of spores from different flowers 
of the same species, has been found to yield more and better 
seeds than self-pollination. 
Very many mechanisms have been developed in different. 
plants to secure this end, which are seen to the greatest 
advantage in the highly developed flowers of the Angio- 
sperms. Pollen may be carried from flower to flower by 
wind or water, or by the agency of insects or other animals. 
From this point of view flowers have been classed as 
anemophilous or wind-pollinated, hydrophilous or water- 
pollinated, entomophilous or insect-pollinated, and zoo- 
philous or pollinated by other animals. 
Of these methods of cross-pollination, the anemophilous 
and the entomophilous are most widespread. The former 
is the more primitive ; indeed, the latter has been gradually 
supplanting it. We find cases now of nearly allied genera 
which illustrate the transition from the one to the other. 
Among the Ranunculacew the flowers of the genus Thalic- 
trum are pollinated by the wind, while those of the more 
specialised genera, Aconitum and Delphinium, depend upon 
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