PLATE 52 



A. Hydrosere of Balrachium, Polamogelon, Nymphaea, Carex, etc., Lily Lake, 

 Estes Park, Colorado. 



B. Xerosere of Leddea, Parmelia, Ceralodon, Grimmia, etc., Pictui-e Rocks, 

 Tucson, Arizona. 



