Southeastern Washington and Adjacent Idaho. 103 



sepala, whose broad leaves and pretty yellow flowers almost com- 

 pletely cover the water for many square meters (Fig. 30). 



Additional floating-leaf aquatics are occasionally seen in mix- 

 ture with the lily. The commonest of these are species of 

 Potam-ogcton and Alisnia plantago-aquatica. 



Where the current is swift enough during a part of the year 

 to keep the bottom relatively free from debris, the lily community 

 may continue for years. But by continued humus accumulation 

 and elevation of the bottom, the habitat becomes invaded more 

 and more completely by plants of the marsh community and 

 finally the lilies disappear entirely. 



The Scirpus-Typha Associes 



Like the preceding, the associes characterized by Scirpus and 

 Typha is found covering only very limited areas considering the 

 region as a whole. I have rarely seen the two dominants grow- 

 ing together, and, in fact, Typha is not abundant. However, ob- 

 servations on Typha in its limited habitat together with a study 

 of its relict associates in shallow water show rather clearly its 

 place in the succession. 



The Scirpus consocies is more widely represented. The domi- 

 nant species are the western tule, Scirpus occidentalis, and Scir- 

 pus microcarpus. While often growing in rather deep water 

 about lake margins where they are sometimes associated with 

 relict Nymphaea and Potamogeton, they likewise occupy boggy 

 places, which in late summer may become mere mud flats (Fig. 

 31). Among the tall stems of the bulrushes is often revealed a 

 distinct layer of Alisma plantago-aquatica, Sagittaria arifolia, 

 and Mentha canadensis borealis, while among these various 

 species of creeping buttercups may be seen. 



Sometimes, as at Tule Lake, a slightly higher and consequently 

 drier habitat gives a fine zonation of Eleocharis palustris and 

 other members of the Eleocharis-Carex community. The pres- 

 ence of the latter among the tule in the drier portions of its area 

 indicates the next stage of development. 



103 



