38 Proceedings of the Ohio State Academy of Science. 



The aquatic vegetation of rather smah, more or less com- 

 pletely separated and isolated ponds do not form as clearly de- 

 fined societies as aerial plants or aquatic plants in larger bodies 

 of water where there are currents."*- They must largely depend 

 on the accidents of dissemination. However, the intensity of 

 the light exposure is a strongly contending factor and in some 

 cases the depth of water and nature of substratum determines 

 the society. 



This is well shown by Wollfiella floridana which forms an 

 almost pure society in one of the small pools in the margin of 

 the open Sphagnum zone, and while it does not occur at all in 

 other small pools with exactly the same factors of environment, 

 it does grow in a large shaded marginal pool vdiolly separated 

 from the small pool and quite a distance from it. The plant is 

 an invader from the south. Up to its discovery in Buckeye 

 Lake it was not reported farther north than southern Missouri 

 and finding its most congenial habitat in the bayous, lakes and 

 ponds of the Gulf states. Buckeye Lake is visited every spring 

 by large numbers of ducks Vvdio stop here to rest and feed in 

 their northward flight. The small fronds of Wollfiella must 

 have been clinging to the feet of some of these ducks and were 

 washed oiT in the small pools in wdiich they were discovered. 

 Later they were carried in the same way to the larger pond. 

 However, after accidental dissemination has taken place, the 

 plant will grow or not grow according to whether or not the 

 habitat be a congenial one, and will form societies with others 

 to which the same environment is congenial, that is, those to 

 which the conditions are suited will survive and flourish and 

 those to wdiich conditions are unfavorable wdll remain of secon- 

 dary importance or succumb entirely. 



Association I is composed of the following societies : 



1. Lemna-Spirodela society 



2. Utricularia minor society 



3. Wollfiella floridana society 



