114 Roosevelt JVild Life Bulletin 



later paper he develops the idea ('08) that desmids are richest where 

 the water is derived from bogs and mossy slopes, but that when these 

 conditions give place to heaths, plains, and arable lands the desmids 

 are less numerous. He also agrees with Bachmann ('08) that the 

 antiquity of the country does not matter, because the whole of 

 Scotland was covered with ice during the last glacial invasion so 

 that " the high geological age cannot be taken into consideration for 

 the development of plankton desmids." W. & G. S. West ('09) 

 have replied to this by pointing out that desmids thrive in spite 

 of and not because of peaty conditions, and that the majority of 

 British desmids grow best in clear water with but little peat. 



Murray's ('05) reason for denying the geological theory is that 

 Scotch lakes of the Caledonian t\'pe lie in geological formations 

 varying from the Lewisian to the Tertiary. He seeks a climatic 

 explanation, holding that the ocean influences the temperature and 

 rainfall of lakes to such an extent that the " western type " of 

 desmid is found only in eastern North America and western Europe. 

 In replying to I\Iur ray's views W. & G. S. West state that what he 

 calls " Tertiar}' lakes " are situated in drainage basins drawing their 

 waters from the older geological formations. 



In comparing Swiss and Scotch lakes Bachmann ('08) is the first 

 to make the point that geological antiquit}^ is of little importance as 

 the whole of Scotland was buried under ice during the recent glacial 

 epoch. He holds that lime is not the factor controlling the distribu- 

 tion of desmids, since Loch Balnagan on the Isle of Lismore has a 

 desmid flora and this whole island is composed of limestone. Bach- 

 mann's explanation for the occurrence of desmids in any region rests 

 upon the chemical nature of the drainage from peaty swamps. He 

 thinks that careful chemical analyses will show certain chemical 

 compounds favoring the growth of desmids. He agrees with an 

 earlier expressed view of Chodat Cgj) that smaller lakes have a 

 richer desmid flora. This correlation of lake size and desmid 

 frequency has been denied by W. & G. S. West, who state that 

 Bachmann's generalization is based upon insufficient knowledge of 

 Scotch lakes, as some of the largest lakes have the richest desmid 

 flora f'09b). 



My investigations of the phytoplankton of lakes in Wisconsin, 

 Ontario, and the Palisades Interstate Park region corroborate com- 

 pletely the view of W. & G. S. West that geological conditions are 

 the prime factors controlling the distribution of plankton desmids. 

 Wisconsin offers an excellent field for testing the hypothesis, since 

 the lakes in the southern part of the state lie in a limestone and 

 sandstone region while the northern part of the state is Archaean. 

 Furthermore, all the lakes are glacial in origin, those of the north hav- 

 ing been formed by the Late Wisconsin glacial invasion and those of 

 the south by earlier invasions. These lakes of both legions are of 

 practically the same age but have quite different floras. Caledonian 

 associations are of frequent, though by no means universal, occur- 

 rence in northern Wisconsin ; southern Wisconsin lakes, with one 

 exception, belong to the Baltic type. The factor governing the 



