Fresh Water Algae in Vicinity of Montreal 405 



When the film was scraped off the damp tiles, it pre- 

 sented the appearance of a blackish green scum. This 

 was found to be composed of Calothrix, Tolypothrix, 

 Oscillatoria, Lyngbya, Desmids and various other uni- 

 cellular forms. During the winter, the aquarium con- 

 taining them was not kept under the same conditions 

 of light and warmth as had obtained in the conserva- 

 tory. Although it was maintained at a higher tem- 

 perature than the others, a marked difference in the 

 color and relative numbers of the algal constituents 

 had taken place. The contents of the culture were 

 now a much lighter green, and while formerly the 

 majority of the individuals had been blue-green, now 

 the green unicellular forms predomniated and many of 

 the blue-greens had entirely disappeared. This is an 

 excellent illustration, on a small scale, of the dominance 

 of the Cyanophyceae under tropical conditions, and the 

 greater adaptation of the Chlorophyceae to conditions of 

 less light and lower temperature which Dr. Fritsch has 

 pointed out in his study of the Tropical Algae. 1 



A good deal of animal life existed in the aquaria 

 throughout the winter. In October, several small 

 crayfish were noticed and removed, as well as in- 

 numerable tiny snails, which were feeding upon the 

 unicellular algae. Vorticella was found in practically 

 every culture, especially in connection with Vaucheria 

 and Ulothrix. Paramoecia were also frequently no- 

 ticed, often containing unicellular forms of algae which 

 they had engulfed. Amoeboae were not so plentiful and 

 no Hydra were observed in any of the cultures, al- 

 though a special search was made for them. Daphnia, 

 Crypris and Cyclops were quite plentiful in aquaria 

 which contained a quantity of water-weed. It was in- 

 teresting to observe that apparently Oscillatoria was 

 not used by any of these forms as food, and that in 

 several small aquaria where it appeared in large 

 quantities the. animal life disappeared shortly after the 

 unicellular green algae had been exhausted. This 



