CHAPTER XLIX. 



PLANT FORMATIONS. 



984. The general formations. Wherever the conditions of en- 

 vironment are such as to develop one or another vegetation 

 type in such abundance that it becomes the dominating vegeta- 

 tion type of the region or area it is known as a formation. A 

 single plant or a few plants may represent a vegetation type, 

 but do not constitute a formation. The massing together of 

 a vegetation type, though it may be represented by many widely 

 different species, so that the area is characterized by this type 

 as the dominant one, constitutes a formation. There may be 

 other types mixed which either appear at certain favorable 

 seasons (example, the rainy-season flora in the desert forma- 

 tions) or represent a few subordinate individuals. The total 

 combined dominant vegetation of any one type constitutes a 

 general formation. The general formations may be grouped 

 first in four divisions. 



1. Climatic Formations. 



2. Edaphic Formations. 



3. Aquatic Formations. 



4. Culture Formations. 



I. Climatic Formations. 



985. The plant covering of the earth is not uniform. This is 

 due in a great measure to the lack of uniformity in climate, 

 topography, and soil. Climatic influences extend over wid^ 



