250 CLIMAX AND SERE 



low, or to reverse the order. The reverse order was chosen, but not 

 without misgiving, and accordingly the last task is to describe enough 

 natural phenomena to illustrate the general principles that have been 

 brought out. This of necessity consists in describing at least three 

 major communities — a terrestrial, a fresh-water, and a marine one. 

 The treatment of all the major communities of northern North 

 America is a major task in itself, though a provisional account is en- 

 tirely possible. Fresh-water communities have not been sufficiently ex- 

 plored from our viewpoint, and the great variety and meager knowl- 

 edge of marine communities make more than a cursory treatment im- 

 possible. The major communities or biomes (usually termed biotic 

 formations, but we have in various earlier papers substituted "biome" 

 as a much more convenient term of the same connotation) are the 

 desert, the chaparral, several in the coniferous forest group, the tun- 

 dra, alpine meadow, deciduous forest, and grassland. The last was 

 chosen to illustrate general principles because it is probably most com- 

 pletely known. 



