PLANT SOCIETIES 



471 



the same climatic area, dependent on soil conditions, or success 

 in seeding and ground-graining of the different species in com- 

 petition, etc. 



Fig. 418. 



Mature forest of redwood (Sequoia sempervirens). Bureau of Forestry, U. S. Dept. Agr., 

 Bull. 38. 



640. 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 foliage through which some light filters down 

 into the interior. Where the forest is uneven there are open 

 places in the canopy which admit more light, in which case the 

 undergrowth may be different. The interior of the forest lies 

 between the canopy and the floor. It provides for aeration of 



