114 MORPHOLOGY 



allogamy, while in others the effect of foreign pollen 

 is more effective or prepotent. 



CHAPTER XVI 



FLOWERS IN RELATION TO POLLINATING 



AGENTS 



For the purpose of crossing, the help of certain ex- 

 ternal agents is necessary. According to the nature 

 of this agency flowers have been grouped into three 

 principal groups, namely, (i) anemophilous or wind- 

 flowers, (2) ENTOMOPHiLOUS Or inscct-flowers, and (3) 

 AQUAPHiLOUS Or watcr-flowers. 



Anemophilous or wind-flowers have certain charac- 

 ters in common which distinguish them from insect- 

 flowers. Thus wind-flowers are inconspicuous, or 

 small and dull in colour, and wanting in nectar. 

 They produce a much greater quantity of pollen- 

 grains than the insect-flowers, as the pollen-grains 

 run a great risk of being washed or blown away 

 during their transit. Moreover, the pollen-grains of 

 these flowers are smooth, light, dry, dust-like, and 

 easily blown about. The stigmas are often of con- 

 siderable size and branched {Trewia, Castor-oil) (see 

 figs. 236, 237), or richly provided with feathery out- 

 growths (Grasses) (see figs. 271, 273), or drawn out 

 into long threads (Maize) — which are special adap- 

 tations for catching wind-borne pollen. The anthers 

 and stigmas are exposed to the air, and this exposure 

 is often enhanced by the plants shedding their leaves 

 at the time of flowering. The anthers are often 

 exserted and versatile, or else the whole male inflor- 



