11 



of wax giving the plaut a glaucous appearance, etc. This apparent 

 anomaly is sometimes ascribed to the coldness of a wet soil, which 

 diminishes the water-absorbing capaoitj^ of the root system and thus 

 renders necessary the same contrivances to prevent too rapid transpi- 

 ration that we see in plants inhabiting very dry soil. The smallest 

 amount of xeropbile habit is exhibited by C. canadensis and its nearest 

 allies, especially when growing in shaded ground. On the other hand, 

 the purpurascens group, with the exception of G. tweedyi, are "bunch 

 grasses" with marked xerophile adaptation, conspicuously glaucous, 

 having low, strict culms with tunicated bases in strong clumps from 

 short, strong rootstoeks, thickish, strongly involute, narrow leaf 

 blades, etc. 



An absolnte ecological classification of the species is impracticable, 

 for the same species may be under different conditions either hydro- 

 phile, mesopbile, or xerophile. As has already been noted, this is fre- 

 quently the case with species which toward the north inhabit dry, 

 sunny situations, but further south take refuge from the increasing 

 heat in moist woods or cold swamps. The following classification is 

 based partly upon that of Warming.' A number of species are entirely 

 omitted, no data as to their habit being available. Others are enu- 

 merated under more than one association class. 



A. Hydrophytes. 



1. Open marshp:s and wet meadows. — C. canadensis, langsdorffii, scrihneri, 



maeoHiiiana, nef/lecta, niicrantlia, laxiflora, hyperborea (especially var. eJongaia), 

 intxpansa, cras'^if/liimis, cinnoides, hreciseta, holanderi, deschampsioides, aleut- 

 ica (po.ssibly halopliile). 



2. Sph.\gnum bogs. — C. cinnoides (sometimes), alaskana (.?). 



3. Low, MOIST WODDS AXD THICKETS (ALMOST A :MES0PHILE ASSOCIATION). — 



C. canadensis (sometimes), lanijsdorffii (sometimes;, blanda, neglecia horealis, 

 suksdorjii (normally xerophile). 



4. Wet cliffs. — C. hyperborea aniericana (sometimes), nienioralis (sometimes). 



B. Xerophytes. 



1. <3n or among rocks. — C. purpurascens, vaseyi, howeUii, scopulorum, lahradoriea, 



hyperborea (sometimes). 



2. Sandy or gravelly shores of lakes and rivers. — C. mbtscens, hyperborea 



(sometimes), hyperborea aniericana (sometimes), hyperborea elon(ja1a (some- 

 times), crassiglumis (sometimes), breriseta lacnstris (probably often hydro- 

 phile). It is doubtful whether this associatiou is properly xerophile. 



3. Sand hills. — C. hyperborea americana (sometimes). 



4. PiiAiniEs and "' bench LANDS." — C. montaneiisis. 



5. Upland woods. — C, porteri, memoralis, suksdorjii (usually;, rubescens, purpu- 



rascens (sometimes), vilfaeformis, kotlerioides. 



C Halophytes. 



Coast marshes. — C. alentica(?). 



In regard to abundance of individuals, the xerophile species are 

 either coj^ious or sparse, but usually scattered. (C suhsdorfii is an 

 exception, for in the Cascade Mountains of Oregon and Washington it 

 grows socially, sometimes covering the ground in the pine woods to 



' Lehrb. der oekolog. Pflanzengeogr. Deutsche Ausgabe, 1896. 



