6 Proceedings of tluc Ohio State Academy of Science. 



tween the concepts of formation, association, and society; but 

 as to the vahie of the respective terms. Griesebach""' was the 

 first to employ the term formation in connection with phyto- 

 geography. To him a "phytogeographical formation" is a group 

 of plants which has a fixed physiognomy, such as a meadow or 

 forest. Warming"^ writes : — "A formation may then be defined 

 as a community of species, all belonging to definite growth 

 forms, which have become associated together by definite ex- 

 ternal (climatic of edaphic) characters of the habitat to which 

 they are adapted. Consecjuently, so long as the external condi- 

 tions remain the same, or nearly so, a formation appears with a 

 certain determined uniformity and physiognomy, even in dif- 

 ferent parts of the world, and even when the constituent species 

 are very different and possibly belong to diff'erent genera or 

 families." 



Hence Warming's concept agrees with that of Griesebach in 

 making physiognomy the controlling factor in a formation and 

 uses this as the basis of classification. Glements'' also sees the 

 formation as an organic unit conditioned by the habitat and it 

 must therefore be co-extensive with the latter. Gonsequently 

 his classification of formations is based on habitat. Adams* 

 says : — -"A formation or climax society is composed of a rela- 

 tively limited number of species which are dominant in a given 

 environment of geographic extent. Such dominance implies ex- 

 tensive range, relative abundance and ability to indefinitely suc- 

 ceed or perpetuate itself under given conditions." And 

 Schimper'^^- recognizes two ecological groups of formations, 

 climatic or district, composed of three chief types, woodland, 

 grassland and desert ; and edaphic or local formations, which 

 are conditioned by the soil ; as swamp, rock, sand dune, etc. 

 Graebner''- advocates making the percentage and nature of in- 

 organic salts dissolved in the soil water, the controlling factor 

 in the character of vegetation. He therefore recognizes the 

 groups of formations; i, where the water contains a high per 

 cent of mineral salts ; 2, where the per cent of mineral salts 

 (supposedly available to plants) is low; and 3, saline water. 



