325 



been found as secondary species in several stations, and, in addition 

 cardinal-flower {Lobelia cardinalis) in a single station. In a few 

 of the ditches along the railway, where this association has found its 

 way, Spartina michaiLviana , Lobelia cardinalis, and a few plants of 

 Iris versicolor take the part of secondary species. Didichium arundi- 

 naceum, a typical bog plant, is present in this region in only two 

 very small boggy places in the midst of a succeeding Popnlus-Salix- 

 C or II us thicket, where it was accompanied by Carex sp. 



Along the shores of Dead Lake, except for a few places where 

 the Castalia-N ymphaca association exists, this association of sedges 

 forms the outermost zone of vegetation visible above the water. At 

 the outer edge it is formed solely of two species of Carex — Carex 

 lanuginosa, and the other was probably Carex filiformis, although 

 none of its flowering culms were obtained. Nearer the shore are 

 invaders of associations occupying shallower water. Among these 

 invaders is Scirpns validns, which may, in other lakes, grow in much 

 deeper water than the Carex does in the Dead Lake. This leads to 

 the conclusion that, although most of the acjuatic and semiaquatic 

 plants are closely restricted within certain depths of water, their 

 position in any given locality is determined by competition of asso- 

 ciations rather than by the dift'erent physical requirements of the 

 plants. The same relative arrangement is maintained within the 

 hmits of the requirements of the individual plants in different locali- 

 ties, even though the absolute conditions may vary greatly. 



LIST OF THE SPECIES OF THE CAREX ASSOCIATION 



Dominant Species 



Carex fdiforviis Carex sfipata 



Carex lanuginosa Carex buxbanmii 



Carex stricta Carex spp. 



Carex comosa Didichium arundinaccum 

 Carex riparia 



Secondary Species 

 Utricularia vulgaris auicrkana Acortis calamus 

 Lobelia cardinalis Bchinochloa crusgalli 



Spartina michauxiana 



Invading Species 

 Iris versicolor Typha latifoUa 



Scirpns validns 



