3^8 MINNESOTA BOTANICAL STUDIES 



Castalia odorata Potaiiiogctoii iiataiis 



Nymphaea advena 



While these three species are generally associated, combinations 

 of any two of them may occur, and in some instances only a single 

 species is to be found representing the associes. These species grow 

 in water from one to six feet in depth, the best development being in 

 from two to six feet of water. 



The following plants occur more or less abundantly as secondary 

 species of this associes : 



CeratopJiylhnn devicrsimi Potamogetoii pcctinatus 

 Myriophylhmi sp. Utricularia vulgaris. 



Potaniogcloii pcrfolialits Zaiinichcllla paluslris 



Polygonum ouipJiibiiiiii and BatracJiiuui fricliopylluiii occur oc- 

 casionally in this zone, but never very abundantly. Among the other 

 plants, floating on the surface, are to be fovmd duckweeds in more 

 or less abundance. The growth of waterlilies so that their leaves 

 cover the surface of the water more or less completely greatly checks 

 or prevents the development of submerged aquatics. 



(3) Scirpus-Zicaiiia Associes 



The reaction of the plants of the Castalia-Nymphaea associes in 

 retaining and binding into a soil the sedimentary material washed 

 into the lake, as well as by the accumulation of the decayed remains 

 of the water-lilies and pondweeds, causes the lake shore to be built 

 up more rapidly, thereby enabling Scirpus, Zisania, and other species 

 of this associes to invade and become established. 



The lowering of the water-level by partial drainage of a lake or 

 by any other cause would result in the movement of the Castalia- 

 Nymphaea zone out into deeper water to be replaced by the Scirpits- 

 Zisania zone, or if the lowering of the water-level were sufficient 

 the latter would invade to the exclusion of the former. 



Consocies : The associes consists of several consocies which may 

 occur all together or in various combinations ; or, in other instances, 

 a single consocies may be the only representative in this stage of 

 development. The typical consocies are : 



Phragmites phragmitcs Typha latifolia 



Scirpits occidentalis Zisania aquatica 



Scirpus validus 



