322 The Ohio Journal of Science [Vol. XIX, No. 6. 



Valley. Although the oases, to be found in spots where con- 

 ditions have permitted the recovery of the herbaceous plants, 

 are conspicuous in the desert valley, their influence in the 

 revegetation of the great bare areas is, from the nature of the 

 case, quite limited. There are three ways in which they affect 

 revegetation. 



First, by direct extension out into the bare areas. Only 

 two of the species present have sufficiently developed the 

 power of sending out runners to be important in this respect. 



Photograph by Robert F. Griggs 



BEACH GRASS SENDING RUNNERS INTO BARE ASH. 



Runners of the current season (1916) are sterile, but the shoots that came through 



in 1915 have fruited. The rate of extension is about four feet per annum. 



The beach grass, (Elymus arenarius), is especially adapted to 

 cope with shifting sand, and in many places in the vicinity of 

 the shore it has been locally of great importance in renewing 

 the plant cover. (See page 321.) Comparison of .photographs 

 taken in successive years and observation of the plants- shows 

 that the rate of extension is about four feet per annum. 



The horsetail, (Equisetum arvense), was able to penetrate 

 deposits so thick that nothing else could come through. Its 

 capacity for penetration is most strikingly shown in the bottoms 



