PLANT FORMATIONS. S 2 7 



attempting to decide what system of terminology should be used, 

 the author feels it is best in this treatise for elementary use to 

 employ the terminology given above. The discussions here will 

 center on the society, since it is believed that it will be more 

 useful in this elementary work to treat the subject rather from 

 the broad standpoint of the plant society, showing the interrela- 

 tion of members of different grades and the general relation of 

 dominant members to environment. The various systems used 

 by different writers can be found in their works listed at the close 

 of this part. 



1005. Complex character of plant societies. In their broadest 

 analysis all plant societies are complex. Every plant society has 

 one or several dominant species, the individuals of which, because 

 of their number and size, give it its peculiar character. The 

 society may be so nearly pure that it appears to consist of the 

 individuals of a single species. But even in those cases there are 

 small and inconspicuous plants of other species which occupy 

 spaces between the dominant one. Usually there are several or 

 more kinds in the same society. The larger individuals come 

 into competition for first place in regard to ground and light, the 

 smaller ones come into competition for the intervening spaces 

 for shade, and so on down in the scale of size and shade tolerance. 

 Then climbing plants (lianas), and epiphytes (lichens, algae, 

 mosses, ferns, tree orchids, etc.), gain access to light and support 

 by growing on other larger and stouter members of the societ T , 

 (See evergreen tropical forests, Chapter L.) 



Parasites (dodder, mistletoes, rusts, smuts, mildews, bacteria, 

 etc.) are present, either actually or potentially, in all societies, and 

 in their methods of obtaining food sap the life and health of their 

 hosts. Then come the scavenger members, whose work it is to 

 clean house, as it were, the great army of saprophytic fungi 

 (molds, mushrooms, etc.), and bacteria ready to lay hold on dead 

 and dying leaves, branches, trunks, roots, etc., disintegrate them, 

 and reduce them to humus where other fungi change them into a 

 form in which the larger members of the plant society can utilize 

 them as plant food and thus continue the cycle of matter through 



