PAPERS ON BOTANY 



125 



as Park and East lakes, are found in Boulder Park and hav- 

 ing been rather carefully studied the succession, may be taken 

 as representative of that of this class of mountain lakes. The 

 soil at the bottom and shores of the lake consists of the orig- 

 inal glacial gravels with a very small amount of alluvium 

 carried in by tributary streams, and a larger or smaller amount 

 of peaty vegetation. The waters are nearly stagnant on ac- 

 count of the small amount of run-off from surrounding areas. 

 The larger of these lakes is only about 3 to 4 feet deep, and 

 the other but little deeper, the conditions being similar to 

 such shallow lakes of the Chicago area as Wolf and Calumet. 

 It would therefore be expected that the same associations 

 would be represented in the two regions especially as no vege- 

 tation shows a wider distribution or greater uniformity than 

 aquatic and sub-aquatic associations, and in fact the same type 

 of succession is actually seen but with several notable differ- 

 ences. 



The algal association in the mountain lakes instead of being 

 abundant and varied as in Illinois, seems to be made up of a 

 comparatively small amount of two species of Spirogyra, some 

 Chaetophora and Drapernaldia and a few blue-green algae of 

 small size. It seems safe to say that there is not more than 20 

 per cent of the mass or number of species of algae found as in 

 similar shallow water in Illinois. The other submerged aquatic 

 community may be termed the Myriophyllum-Batrachium as- 

 sociation, from the two species Myriophyllum spicatum and 

 Batrachium trichophyllum, its only members. The latter is 

 the more abundant, but the mass of the two is small compared 

 with the submerged aquatics of more eastern waters. 



Separated from the associations already mentioned and oc- 

 cupying the shallow water near the shores is the main aquatic 

 community, a pondweed association, characterized by plants 

 with ribbon-like submerged and floating leaves. Its dominant 

 member is a bur-reed, Sparganium angustifolium, whose 

 leaves float on or near the surface, and Potamogeton lonchitis 

 and P. foliosus. This paucity of forms contrasts with the 

 conditions in Illinois where at least twice as many species 

 and double the mass of vegetation are to be found in the cor- 

 responding habitat. The mountain lakes are also deficient in 

 the entire absence of any association corresponding to the 

 water lily or cat-tail associations, but the submerged and float- 

 ing leaves of the pond-weed association are followed at once 

 by the emergent sedges. Perhaps nowhere do the two regions 

 resemble each other more closely than in this stage of the suc- 

 cession known as the sedge swamp, fen, or sedgemoor. It is 



