78 Proceedings of the Ohio State Academy of Science. 



society covers a narrow lens-shaped area not more than 3 feet 

 in its broadest portion. At the normal water level the surface is 

 submerged, but now it is wholly exposed. The Polygonum is 

 tall and vigorous with branches from 3-4 feet tall ; the Nelumbo 

 has large erect leaves and the plants are fruiting freely; the 

 Typha is stunted in growth and sterile, the largest leaves are not 

 more than 4 feet tall. 



This zone is followed by the shore association which covers 

 the low very gently sloping mud flat between the pond associa- 

 tion and the forest. Typha latifolia is the dominant species on 

 the outer and Hibiscus moscheutos on the inner margin. The 

 following two societies are very evident. 



4. Typha-Poh'gonum-Bidens society 



Principal species : 

 Typha latifolia Bidens cernua 



Polygonum emersum 



Secondary species : 



Cyperus strigosus Cicuta bulbifera 



Eleocharis acicularis Bidens frondosa 



Riccia fluitans Roripa palustre seedlings 



Spirodela polyrhyza Hibiscus moscheutos seedlings 



Brachythecium plumosum Polygonum emersum seedlings 



Society 4 occupies a narrow zone less than 3 feet in width. 

 The Typha is larger and more vigorous than in 3, but not fruit- 

 ing; Polygonum emersum is still conspicuous but not nearly so 

 much as in the preceding zone, while the Xelumbo lutea has 

 entirely disappeared and Bidens cernua, represented by a few 

 large plants, has come in. There are but a few of the taller herbs 

 of the secondary species, but an abundant ground-cover of the 

 Cyperus, Riccia and Eleocharis. This zone merges into : 



5. Hibiscus-Typha society 



Principal species : 

 Hibiscus moscheutos Typha latifolia 



