STEUOTUEE OF THE FORMATION 55 



taller-growing Carex stricta and C. cephaloidca, and later by 

 Spartina cynosuroides which frequently attains a height of 

 three meters. 



The distribution, alternation,* and zonation of some of the 

 more important species are worthy of note. Comandra uin- 

 hellata commonly occupies crests and exposed slopes of 

 ridges, where it often numbers 2,000 to the quadrat. Coman- 

 dra is not continuous, however; it disappears entirely for a 

 time, reappearing in greater numbers than befora Coreopsis 

 palmata and Aster multiflorus inhabit crests of ridges and 

 high prairies. These tAvo species occur in copious, definite 

 patches, which frequently alternate. The individuals of a 

 patch are most numerous toward the center, frequently 2,500 

 to the five-meter quadrat, and gradually diminish in size 

 and number as the margins are approached. The above spe- 

 cies are rarely found in controlling numbers in the same quad- 

 rat; the one or the other ranks as copious 1, the remaining 

 ones being subordinate. Aster multiflorus also frequents 

 meadows, "where it forms rather definite patches of robust in- 

 dividuals. Alternation of species is beautifully shown iu the 

 case of Kuhnistera purpurea and K. Candida. The esplana- 

 tion is evident. The former species is much more of a xero- 

 phyte and almost invariably grows on crests of ridges and 

 abrupt or exposed slopes. About midway up the ridge, these 

 two species are of equal importance, while a little lower down 

 the white-flowered form will have almost completely displaced 

 K. purpurea. Kuhnistera Candida is a taller-growing plant 

 and possesses a greater leaf surface than K. purpurea. Ac- 

 cordingly, it is not as well adapted to xerophytic conditions. 

 The distribution of the blazing-stars is also largely dictated 

 by the water-content, and if these plants were as abundant as 

 Kuhnistera, conditions at least as striking would obtain. 

 Laciniaria squarrosa is found on crests of high ridges, a typi- 



*Altemation Is here used in the sense in which it has heen employed by Dr. ClomeTits, i.e.. 

 to apply to snccession in space of species and formations, though alternation of species is 

 alone concerned in this _plnoe. The term "succession" is applied by the same authority to the 

 j^eaomenon of succession in time. 



