188 



COLLEGE BOTANY 



Hydrophytes. — Tkis society includes those plants which re- 

 quire a maximiim amount of water; in fact, plantsi which live 

 submerged in, or floating on, or standing in the water. They 

 include species from all parts of tlie plant kingdo'm, from the 

 lowest to the highest. The most prominent subdivisions are the 

 free swimarning societies, which include the free algae and duck- 



FlG. 102. — Zone formation of vegetation dependent upon depth of water. 



weed; the pond societies, which include the pond weeds, watei 

 lilies, water ferns and the attached algae ; the swamp societies, 

 which include the more or less erect plants which are partly sub- 

 merged, such as the cattails, sedges and various reed plants. 

 The swamp group may also include the sphag-num moss, many 

 of the orchids, cranberries, alders, willows, birches, poplars, 

 tamarack, hemlock and some of the pines. Kice and cranberries 



