PLANT SOCIF.TfES. 477 



(see Chapter IX) which make certain suIjsUiih cs in the soil a\'ail- 

 able to the higher memV^ers of the society. Most ])lant societies 

 are also benefited or profoundly influenced in other wa}'s by 

 animals, as the flower-visiting insects, birds which feed on 

 injurious insects, the worms which mellow up the soil and co\-cr 

 dead organic matter so that it may more thoroughly decay. In 

 short, every plant society is a great cosmos like the universe 

 itself of which it is a part, where multitudinous forms, processes, 

 influences, evolutions, degenerations, and regenerations are at 

 work. 



918. Forest Societies.* — Each different climatic belt or region 

 has its characteristic forest. For example, the forests of the 

 Hudsonian zone in North America are different from those of 

 the Canadian zone, and these in turn different from those in 

 the transition zone (mainly in northern United States). The 

 forests of the Rocky mountains and of the Pacific coast differ 

 from those of the Alleghanian, Carolinian (mainl}' middle United 

 States) or Austroriparian (southern United States) areas. 

 Finally, tropical forests are strikingly different from those of 

 other regions. Similar variations occur in the forests of other 

 regions of the globe. The character of these forests depends 

 largel}' on climatic factors. The character of the forest varies, 

 however, even in the same climatic area, dependent on soil 

 conditions, or success in seeding and ground-gaining of the 

 different species in competition, etc. 



919, General structure of the forest. — Structurally the forest 

 possesses three subdivisions: the floor, the canopy, and the 

 interior. The floor is the surface soil, which holds the rootage 

 of the trees, with its covering of leaf-mold and carpet of leaves, 

 mosses, or other low, more or less compact vegetation. The 

 canopy is formed by the spreading foliage of the tree crowns, 

 which, in a forest of an even and regular stand, meet and form 

 a continuous mass of fohage through which some hght filters 

 down into the interior. \\'here thg stand is irregular, i.e., the 



* For a full discussion of forest societies .<:ee Chapter L in the author's 

 "College Te.xt-book of Botany." 



