For although most of the lakes are soft, those which do have a 

 somewhat alkaline or basic character reflect their chemistry in a 

 noticeably richer blue-green and diatom flora. In Arbor Vitae Lake, 

 Wisconsin, for example, a lake somewhat harder than nearby Trout 

 Lake, a relatively heavy bloom of Gloeotrichia echinulata is sup- 

 ported, and the flora as a whole is the cyanophyte-diatom type. 



A comparison of the algal flora of the northern and northeastern 

 sections with those of the south and southeastern sections of both 

 Michigan and Wisconsin leads to the generalization that in the 

 northern sections the bulk of the algal vegetation is low but the 

 number of species is high. The larger number of species for the 

 northern section is due to the luxuriant desmid flora which abounds 

 in the soft (acid) water lakes and bogs. (See Fassett, 1930; Wilson, 

 1937, 1941, on the larger aquatic plants of lakes in northeastern 

 Wisconsin. ) 



Approximately 200 collections were made from the sandy-crystal- 

 line rock area of northwest Wisconsin (Burnett, Washburn, and 

 Sawyer counties). The lakes here, as has been pointed out, are 

 mostly soft water, with a pH on the acid side. The bottoms 

 and the shores are sandy, with little aquatic vegetation of any kind. 

 Of course there are exceptions. Shell Lake in Washburn County, 

 for example, is a habitat of relatively hard water, supporting a rich 

 blue-green algal flora. This is the only lake in northern Wisconsin 

 from which collections were made that had a bloom of Aphani- 

 zomenon flos-aquae. Although chemical analyses are not at hand 

 for support, one can predict that this lake is relatively rich in nitro- 

 gen, as judged by the cyanophyte-diatom flora. This condition might 

 be expected because the lake lies within the town of Shell Lake 

 and is bordered, in part, by tilled soil, a situation which makes the 

 accumulation of nitrogenous substances possible. In contrast is 

 Round Lake, Sawyer County, a large lake with a considerable 

 amount of shallow water which supports a very scant phytoplank- 

 tonic flora, with filamentous forms poorly represented. Chara spp., 

 at least when collections were made in August, were found to be 

 stunted. There were, however, luxuriant beds of Nitella, a genus 

 which prefers soft water habitats. 



LAKE TYPES AND ALGAL DISTRIBUTION 



Inland lakes of the region fall naturally into four main types as 

 determined by hydrographic features. In their Wisconsin lake 

 surveys Birge and Juday noted and described significant limnologi- 

 cal characteristics peculiar to these classes. Correspondingly, the 



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