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PLANT PHYSIOLOGY AND ECOLOGY 



Bouteloua, Andropogon, Kcdera, Stipa, etc. In certain places 

 two or more of these may meet on nearly equal terms to form a 

 consocies, e.g., a Bouteloim-Kcelera-consocies. More frequently 

 a ridge or slope is controlled by one facies, resulting in an Andro- 

 pogon-consocies, a Stipa-consocies, etc. In some formations 

 consocies are definite, in others they overlap or are indistinct, 

 but in all that possess two or more facies they can usually be 

 recognized. In grassland, however, they are often obscured by 

 the more conspicuous groups of principal species. 



240. The society. An area characterized by a principal species 

 is a society. Unlike the consocies, societies usually do not cover 



Fig.' 86. An Iris society, characteristic of the spring aspect of the aspen 

 formation in the Rocky Mountains. 



the entire formation, but are separated from each other, the gaps 

 being filled by secondary species and by the scattering individuals 

 of principal ones. Societies moreover change with each aspect, 

 as the principal species of one season replace those of the preceding 

 one. In the prairie formation, for example, three characteristic 

 societies of the spring aspect are the Astragalus, the Coviandra, 

 and the Lomatium societies. In the summer aspect these have 



