J72 



for as soon as sufficient soil has accumulated they are superseded 

 by grasses and other vascular plants. These, by means of their 

 interlacing roots and rhizomes bind the soil together more firmly, 

 and in this way a sod is gradually developed. Because of their 

 omnipresence and the abundance of their tough, fibrous roots, 

 the bunch grass {Andropogon scopariiis) and the wire grass {Poa 

 com'pressa) are especially important as sod formers. The wire 



^¥^.- 



r : 



Fig. I. Rock face and crevice vegetation on trap; near summit of West Reck, 

 ISJew Haven. The conspicuous lichen in the foreground is Parmelia conspersa. 

 Among the crevice forms are Leucobryum glaucum and other mosses, Cladonia sp., 

 Woodsia ilvensis, Andropogon scoparius, and Rhus typhina. The tree in the 

 background is Juniperus virginiana. 



grass possesses an additional advantage in that it develops long 

 rhizomes which facilitate the invasion of new territory. There 

 may thus arise a plant society characterized by the prevalence 

 of tall, perennial grasses. Associated with the two grasses already 

 mentioned may occur many other herbaceous plants, some of 

 which are here noted. 



