55 



The fourth group, or parasites, is represented by a single species 

 of seed plant, Orobanche fasciculata, found on the roots of Artemisia 

 caudata in the Hanover area. 



While these four groups are sufficiently distinct to serve as eco- 

 logical units, they are not absolutely separate. The perennial Les- 

 pedeza capitata, with its slender stems and narrow leaves, associates 

 frequently with the true interstitials, and might then well be regarded 

 as one of them. Cy perns Schweinitsii appears now as a bunch-grass, 

 now as an interstitial. Boutelona hirsnta behaves sometimes as a 

 bunch-grass, producing small tufts two to four inches (5-10 cm.) 

 high, but frequently it functions more as a mat and associates with 

 Sclaginella rupestris and Antennaria sp., or, when growing between 

 larger bunches of Koclcria cristata, it might be regarded also as an 

 interstitial. 



The number of secondary species and individuals is naturally 

 greatest in the more open parts of the association and least in the 

 denser portions. The mats may entirely disappear and the inter- 

 stitials be greatly reduced in number when the bunch-grasses are 

 closely agg'regated. The perennials, with their greater resistance to 

 crowding by the grasses, remain throughout and always occupy a 

 prominent place in the association. The close relation between the 

 secondary and dominant plants of an association is seldom better 

 illustrated than in this one, where the presence and disappearance of 

 the interstitials are both correlated with the density and luxuriance of 

 the bunch-grasses. 



The association as a whole is, as already noted, divided into a 

 number of consocies. Some of these are characterized by a single 

 species of grass and may be called pure consocies. Such are those 

 characterized by Koclcria cristata, Lcptoloma cogiiatuin, Stipa 

 spartea, and Care,v Muhlenhergii. A larger part of the association is 

 occupied by several characteristic species and is here termed the mixed 

 consocies. Although the specific composition of the latter varies 

 somewhat from place to place, its general appearance is so uniform 

 that it does not admit of further sulidivision. Besides describing 

 these five, representing natural conditions, it is necessary also to men- 

 tion some of the efTects of cultivation, pasturing-, and burning. The 

 consocies are described in the reverse order of their importance, and 

 the notes on cultural chang'es follow. It will be observed that the 

 fioristic differences between the various consocies are slight. 



The Carex Muhlenhergii Consocies 



The onlv observed examples of this consocies were in the Han- 

 over area, the first in an interdunal depression, the second on the 



