i.] MODES OF TRANSFERENCE OF FOLLEN. 9 



Thirdly, there are many species in which, though the 

 anthers and stigma are contained in the same flower 

 and are mature at the same time, they are so situated 

 that the pollen can hardly reach the stigma of the same 

 flower. 



The transference of the pollen from one flower to 

 another is, as already mentioned, effected principally 

 either by the wind or by insects, though in some cases it 

 is due to other agencies^ as for instance, by birds, or by 

 water. For instance, in the curious Vallisneria spiralis 

 the female flowers are situated on long stalks which are 

 spirally twisted, and grow very rapidly, so that even if 

 the level of the water alters, provided this be within 

 certain limits, the flowers float on the surface. The 

 male flowers on the contrary are minute and sessile, 

 but when mature they detach themselves from the 

 plant, rise to the surface and float about freely like 

 little boats among the female flowers. 



Wind fertilised flowers as a rule have no color, emit 

 no scent, produce no honey, and are regular in form. 

 Color, scent, and honey are the three characteristics by 

 which insects are attracted to flowers. 



Again, as a rule, wind-fertilised flowers produce much 

 more pollen than those which are fertilised by insects. 

 This is necessary, because it is obvious that the chances 

 against any given pollen grain reaching the stigma are 

 much greater in the one case than in the other. Every 

 one, as already mentioned, has observed the showers of 

 yellow pollen produced by the Scotch fir. 



Again, it is an advantage to wind-fertilised plants to 

 flower early in the spring before the leaves are out, 

 because the latter would catch much of the pollen and 



