REPRODUCTION 439 
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 
immediately 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 Delphiniwm depend upon 
insects. The Plantains also afford instances of the replace- 
ment of the one method by the other. 
Anemophilous flowers exhibit certain structural features 
