Bergman and Slallai'd: climax formations 337 



Variations of this sequence may sometimes occur by the omission 

 or sHght development of a stage, or within an associes by the dis- 

 appearance of one or more of its consocies. Such variations will be 

 indicated in the discussions of the associes of the successions and 

 more fully treated in a later report. 



(1) Chara-Fhilotria Associes 



This associes appears only in deep water, varying in depth from 

 six to twenty feet. In such places succession may begin with the 

 invasion of Chara, Philotria, and other dominants of the associes. 

 The character of the bottom plays a part in the ecesis of these 

 plants. On sandy or muddy bottoms they establish themselves read- 

 ily, but on coarse gravel or rock this is not possible. The lakes of 

 northeastern Minnesota, which occur in basins of rock, are accord- 

 ingly devoid of submerged aquatics. 



Consocies : Chara is the first species to invade the lake bottoms, 

 and consequently in the deeper places is often the only species pres- 

 ent. In somewhat shallower water, perhaps to a depth of fifteen 

 feet, Utricidaria vulgaris appears, and associated with it are 

 Philotria canadensis and Myriophyllum sp. Utricidaria, Philotria, 

 and Myriophyllum extend from the deeper water out to the Castalia- 

 Potamogeton zone ; they are always submerged, but often form very 

 dense masses of vegetation. 



Secondary species : Associated with them in water up to ten or 

 twelve feet in depth are : Potamogeton perfoliattis and Potamogeton 

 :iosteraefoHus. 



(2) CasiaUa-Nymphaca Associes 



The principal natural causes contributing to the development, of 

 this associes are: (1) the deposition of material eroded by streams 

 and transported into the lake, filling it up until the species of the 

 associes are able to enter and establish themselves, (2) the accumu- 

 lation of decayed remains of the pioneer plants of the lake bottoms. 

 The latter cause works very slowly in comparison with the estab- 

 lishment of plants of the following associes. Drainage of the lakes, 

 if not complete, would lower the water-level so that plants of this 

 associes would find favorable conditions for growth. 



Consocies : Three species are typically found as consocies in 

 this associes : 



