yo iPostclsia 



This is especially to l^e observed upon stream 

 deltas for the uneven stream deposits and the 

 changing contour of these bars do not permit 

 the various inhabitants to establish themselves 

 with permanency. Where on the other hand, 

 the beach does not undergo comparatively rapid 

 changes, vegetation is not of such transient char- 

 acter and here too less hardy forms are able to 

 compete for tlie ground and maintain them- 

 selves with varying success. The group as a 

 whole is of more or less open growth. The 

 various species of grasses enumerated grow^ in 

 scattered tufts and do not build up a character- 

 istic turf. The struggle here is not so much of 

 species against s])ecies as that of the entire 

 society against adverse edaphic conditions. 

 That the different representatives share much 

 alike in this fate is showm by the fact that no 

 one species preponderates in any marked degree 

 over the others. 



c Back beach. 

 This zone at Lake San Juan can be separat- 

 ed, according to present topographic conditions, 

 into a rocky and a non-rocky region. The char- 



