402 Canadian Record of Science 



was noticed that in such aquaria as had a coating of 

 Oscillatoria, Stigeoclonium, Chaetophora or Ulothrix 

 about the sides, growth was much more successful than 

 in those where the filaments were exposed to the direct 

 sunlight. 



The beneficial effect of a comparatively low tem- 

 perature was also apparent. The most favourable 

 range was from 5° to 15° C. Under this temperature, 

 Spirogyra, Vaucheria and Cladophora lived most suc- 

 cessfully, whereas they appeared less healthy and were 

 shorter-lived when the temperature of the culture was 

 raised above 20° C. Mougeotia, Ulothrix, Stigeo- 

 clonium and the Desmids seem to require a slightly 

 higher temperature than other forms, usually appear- 

 ing in aquaria where the temperature had been raised. 

 Oscillatoria also showed in a marked degre the effect of 

 a higher temperature, the blue-green tufts of this form 

 always appearing in a culture within a day or two after 

 the temperature had been allowed to rise to 25° or 

 30°C. 



In the case of the filamentous - £orms like Clado- 

 phora and Vaucheria, the lower temperature probably 

 proved favourable to growth because of the increased 

 amount of oxygen and carbon dioxide, which would be 

 dissolved in the water at the lower temperature. The 

 same consideration would also apply to the Spirogyras, 

 though as a rule they can grow in less aerated water 

 than Vaucheria and Cladophora, probably because 

 they possess thinner cell walls and numerous chloro- 

 plasts which permit an easy diffusion of gases. 1 



Mougeotia, Ulothrix, Stigeoclonium, Oscillatoria 

 and the Desmids, on the other hand, were probably 

 collected in the form of spores, and an increase of 

 temperature, in the cultures in which they happened 

 to be, induced germination. 



It was found impossible to keep Anabsena alive in 

 the laboratory for more than a week or two after 

 collection. Generally, after a few days, the filaments 



