46 



both. The subjoined tabular view will express the classification used, 

 while the arrangement of the associations in the descriptive matter 

 follows as nearly as possible their successional relations. 



Classif^ication of the Plant Associations 



A. The vegetation is dominated by grasses, occupying a relatively stable habitat 

 with low water-content. The secondary species occupy the interstices between 

 the stools of grass. -pj^^ Prairie Formation of the Prairie Province. 



a. The movement of sand is slow; several species of bunch-grass are pres- 



ent and many secondary perennial species. 



The Bunch-grass Association. 



b. Sand movement is more rapid; the area is dominated by Panicum 

 pseudopubescens and the secondary species are chiefly annuals. 



The Panicum pseudopubescens Association. 



B. The vegetation is very sparse and open, occupying usually a very unstable 

 habitat due to rapidly shifting sand ; there is little distinction between dom- 

 inant and secondary species. ^^^ Blowout Formation of the Prairie Province. 



a. The sand movement is chiefly due to removal by gravity; the vegeta- 



tion consists of reHc grasses and perennials. 



The Windward Slope Association. 



b. The sand movement is due chiefly to removal by wind ; the extremely 

 sparse vegetation consists of deep-rooted perennials. 



The Basin Association. 



c. The sand movement consists chiefly of a mere redistribution or of 

 gradual deposition ; the vegetation is composed chiefly of annuals. 



The Blowsand Association. 



d. The sand movement consists chiefly of a mere redistribution; the vege- 

 tation is dominated by the sand-binding perennial, Hudsonia tomcntosa. 



The Hudsonia Association. 



e. The sand movement consists chiefly of deposition; the vegetation is 

 composed of sand-binding perennials with accessory annuals. 



The Deposit Association. 



f. The vegetation occupies a fossil soil, uncovered by continued sand move- 



ment; the dominant species is Stenophyllus capillaris. 



The StctiophyUns Association. 



C. The vegetation is dense, closed or nearly so, with grasses only as secondary 

 species; the sand is stable, with usually relatively high water-content; the 

 formation is developed in deep depressions. 



The Swamp Formation of the Deciduous Forest Province. 



a. The vegetation is semixerophytic, characterized by slender perennials. 



The SoUdago Association. 



b. The vegetation is truly mesophytic. 



1. The vegetation is dominated by willows.^ ^^^ ^^^.^. Association. 



2. The vegetation is dominated by mat-forming mosses. 



The Polytrichum Association. 



c. The vegetation is hydrophytic The Swamp Association. 



