CLASSIFICATION OF PLANT COMMUNITIES 347 



distinguished — the chmatic or district formations, the char- 

 acter of whose vegetation is governed by atmospheric precipi- 

 tations, and the edaphic or local formations, whose vegetation 

 is chiefly determined by the nature of the soil." 



It is the opinion of the writer that the only logical way to 

 reconcile the divergent views of various authorities regarding 

 the interpretation of the word formation is to retain the 

 classification of Schim.per, distinguishing between edaphic for- 

 mations on the one hand and chmatic formations on the other, 

 but modifying Schimper's concept to harmonize ^^dth the de- 

 velopmental concept as set forth in preceding paragraphs of 

 this paper. 



The climatic formation-type. On different portions of the 

 earth's surface, owing to the existence of various parallel types 

 of chmate, there have been developed correspondingly numerous 

 parallel types of climatic formation. Thus, as deUmited on 

 Schimper's map (19, map 3), the sclerophyllous woodland 

 formation of southern Cahfornia is paralleled by the sclero- 

 phyllous woodland formation of the Mediterranean region and 

 that of South Africa. Similarly, the short-grass formation of 

 North America finds its ecological counterparts in the grassland 

 formations of Russia and China. Different individual climatic 

 formations which have thus developed in response to the same 

 type of chmate and which as a result agree with one another in 

 their ecological aspect, even though they differ (as they usually 

 do) in their floristic composition, are to be considered as belong- 

 ing to the same climatic formation-type. Like the association- 

 type and the edaphic formation- type, the climatic formation- 

 type is an abstract conception. It may be defined as : a type of 

 chmatic formation correlated with a given type of climate. 

 While, in practice, their exact dehmitation is of course a matter 

 of considerable difficulty, in a general way it is possible to divide 

 the vegetation which clothes much of the earth's surface into 

 a relatively small number of formation-types. 



Brockmann-Jerosch and Riibel, in their universal classifica- 

 tion of plant communities (2) have distinguished four vegeta- 

 tion-types (hgnosa, prata, deserta, and phytoplankton) and have 



