lake bottoms of southern Michigan. The marl lakes are character- 

 istically poor in both plankton and higher vegetations {Potamoge- 

 ton, Ceratophyllum, Myriophyllum). In such hard water lakes, 

 however, where nitrogenous substances and phosphorus are pres- 

 ent, higher aquatic plants become so abundant as to cause serious 

 problems. 



The few collections that have been made from the Erie Low- 

 lands (including the Detroit area and the extreme southeast of 

 Michigan) show that here too the algal flora, like that of southern 

 Wisconsin and Minnesota, is characteristically the hard water type. 



Wisconsin 



The geological history of this state has determined six general 

 soil areas which are shown in Figure 1. Except for the unglaciated 

 limestone in the driftless area of the southwest corner of Wisconsin, 

 the soils represent deposits from the various periods of glaciation. 

 They overlie three chief types of basic rock formation shown in 

 Figure 2: crystalline rock in the northern third of the state; lime- 

 stone in the southern third and extending into the Green Bay 

 region; a sandstone area in the middle portion of the state and the 

 extreme northwestern corner. These soil types, in combination with 

 their respective underlying rock formations, determine four great 

 areas of the state, which, generally speaking, show corresponding 

 differences in lake types and algal floras. 



First, there is a glaciated limestone region, the northern bound- 

 ary of which extends diagonally east to west, beginning just above 

 Green Bay in Marinette and Oconto counties and ending with 

 Green County in the south-central part of the state. This highly 

 calcareous area occupies most of the southeastern third of Wiscon- 

 sin. Second, there is an unglaciated limestone area made up of six- 

 teen southwestern and western boundary counties. Because this is a 

 driftless area there are few lakes in the region. As would be expect- 

 ed, the lakes in the entire lower portion of the state, both southeast 

 and south-central, are rich in calcium, magnesium, carbonates, 

 and bicarbonates. These qualities, together with such factors as 

 relative shallowness and high summer temperatures, determine the 

 character of the algal flora which, in general, is the cyanophyte- 

 diatom, or hard water type. 



In Lauderdale Lake, Walworth Gounty, Wisconsin, for example, 

 the number of species of Chlorophyta and Gyanophyta are about 

 equal, but the abundance of the latter far exceeds the bulk of the 

 green algal vegetation. This is in keeping with the general observa- 

 tion that where water is warm, rich in fixed and half-bound carbon 



