Fresh Water Algae in Vicinity of Montreal 393 



species of Anabasna which lives symbiotically with the 

 Hepatic, Blasia, and a Nostoc which is similarly con- 

 nected with Anthoceros. Both of these forms occur on 

 the Island of Montreal. Then, there are several species 

 of Chlorella which are associated symbiotically with 

 Hydra viridis. 



Many of the most beautiful Alga? are very small and 

 grow in gelatinous films on the leaves and stems of sub- 

 merged plants. Other minute forms, together with an 

 abundance of Peridinieae and Copepoda, abound in the 

 surface waters of lakes and rivers, and constitute a great 

 part of the fresh-water plankton which forms the food 

 of most of the smaller aquatic animals, which, in turn, 

 serve as the food of the lake and river fishes. 



Algge exist under very diverse conditions of tempera- 

 ture. Many forms survive freezing. Filaments of 

 Spirogyra and Vaucheria, which I have melted out of the 

 ice, appear to suffer in no way from the low temperature. 

 Species of the Cyanophyceas and Bacillariacese are found 

 in the Arctic regions and on mountain tops, forming the 

 principal parts of the snow-flora and passing their entire 

 existence on snow or ice. Other members of the same 

 groups flourish in the waters of hot springs, where the 

 temperature reaches 85° C. 



The comparative richness of any district in fresh- 

 water alga? depends largely on its physical and geo- 

 logical features. West, in his "British Fresh-water 

 Algas, ' ' 9 states that a mountainous region may be ex- 

 pected to show more forms than a flat district. The 

 latter will contain the larger filamentous algge, and an 

 abundance of unicellular forms. On the other hand, 

 a mountainous region will show forms belonging chiefly 

 to the Cyanophyceae and Conjugatas, especially numerous 

 species of Mougeotia and Desmids. Moreover, he says ; 

 ' ' If the mountains consist of the older Palaeozoic rocks or 

 the Pre-Cambrian rocks, there is a surprising numerical 

 increase not merely of species but also of individuals, 

 and in comparison a mountainous region of carboni- 



