304 PLANT-LIFE 



a few submerged flowering aquatics. The Grass- Wrack 

 (Zostera) is an example. The manner of pollination is 

 described on p. 195. The pollen of various species of 

 Halophila, which flourish in tropical seas, is conveyed 

 to its destination by currents of water. The Vallisneria 

 (Vallisneria spiralis) is a plant commonly introduced 

 into fresh-water aquaria. It is a native of Southern 

 Europe, and the male and female flowers are borne on 

 separate plants. The female flowers are terminal on 

 long spiral stalks, which enable them to reach the sur- 

 face of the water readily. The male flowers are de- 

 veloped under water, and while in that medium are 

 closed, so that the water cannot penetrate to the 

 stamens and damage the pollen. When ripe, these 

 male flowers detach themselves, and rise to the surface. 

 Arrived there, they open, the stamens project, and the 

 anthers burst, liberating their pollen. The detached 

 males float on the surface until they drift to female 

 flowers, also exposed on the surface. Fertilization en- 

 sues, after which the female flowers sink, and ripen their 

 seeds. In the case of Vallisneria, and also in that of 

 some other aquatics, water is really not the pollinating 

 agent, for, as we have seen, the pollen is not transferred 

 in the water, but on its surface, and the drifting of the 

 male flowers to the females must be due to wind. 



In a large number of plants wind is the pollinating 

 agent. It has been estimated that about 10,000 species, 

 or nearly a tenth of the total number of Flowering plants, 

 are wind-pollinated, or, as they are technically termed, 

 " anemophilous " (Gr. anemos, wind; phileo, I love). 

 The category includes Conifers, Hazels, Alders, Birches, 

 Oaks, Beeches, Poplars, Planes, Walnuts, and many 



