321 



the permanently standing water during the season of 1909. Its nearest 

 possible source was about forty meters away, and the probable agent 

 in dispersal was a marsh bird. Occurring with Nyinphaea in some of 

 these artificial situations, as well as in natural ones, were Polygonum 

 mnphibuim hartzvrightii and Sparganium eiirycarpuui, which more 

 properly belong to other associations. In areas in the western part 

 of Lake County, Illinois, this association is often dominated during 

 the fall by the tall stems of Pontederia cordata, but until three exam- 

 ples of it were found during the summer of 19 10, this plant was what 

 Hai-per (1906:329) has termed a "notable absentee." 



IvIST OP THE SPKCIES OE THE CASTAEIA-NYMPHAEA ASSOCIATION 



Dominant Species 

 Castalia tuberosa Nymphaea advena 



Secondary Species 



Pontederia cordata Po tamo get en spp. 



Ceratophylhini deinersuni Blodea canadensis 

 Potamogeton natans 



Relic Species 

 Chara sp. 



Species of accidental occurrence 

 Polygonum am phihiiim hartzvrightii Sparganium eurycarpum 



THE RANUNCUEUS AQUATIEIS CAPIEEACEUS ASSOCIATION 



After the establishment of the Nymphaea association around the 

 margin of many of these ditch pools, plants of Ranunculus oquatilis 

 capillaceus appear at the lower (inner) edge of the Nymphaea. 

 Thence they spread out, and in time usually cover the surface of the 

 open water. The vegetation floats out towards the center of the 

 water, while the roots remain in the Nymphaea. The mass of Ranun- 

 ctdus becomes so dense in some of the smaller pools that it can sup- 

 port the weight of marsh birds. The flowers of this plant are 

 borne two or three centimeters above the water on slender hollow 

 stems. While the plant is in bloom the pool appears almost wdiite. 

 With the R. aquatilis capillaceus are occasionally a few plants of i?. del- 

 phinif alius, and mixed in with the leaves are colonies of Lemna minor. 

 This association is one of the many small associations of water- 

 plants which are rather local in their distribution even in a given 

 area. Ultimately it will be displaced by the Castalia-Nymphaea as- 

 sociation. 



