406 Canadian Record of Science 



may be due to the toxic qualities of the Oscillatoria 

 which are suggested by the disagreeable gas that it 

 gives off. 



Periodicity in Spirogyra. 



A brief consideration of the theories advanced by 

 several botanists who have studied the question of 

 periodicity in the occurrence and sexual reproduction 

 of Spirogyra may serve to summarize and explain some 

 of the results which have been noted in the foregoing 

 pages. 



Benecke 2 has advanced the theory that conju- 

 gation in Spirogyra is due to the failure of ammonium 

 salts, supposed to be removed from the the water by 

 angiosperms which increase in size and abundance as 

 the season advances. He placed Spirogyra communis 

 (Hass.) Kiitz, in various media, in bright light, with 

 temperatures from 12° — 20° C, and found that in 

 nitrogen-free solutions conjugation took place at once 

 or in a short time. If parallel cultures were run, in 

 which NH 4 or N0 3 had been added in appropriate 

 amounts (.05%) to any of the above media or substi- 

 tuted for one of the constituent salts, no conjugation 

 took place, but good vegetative growth ensued generally. 



Danforth 3 repeated these experiments, using other 

 species. Of the five species investigated, three 

 failed entirely to give the same results as had been 

 obtained in Benecke 's work, the fourth failed in every 

 case but one, and the remaining species, S. Grevilleana 

 (Hass.) Kiitz seemed to agree more closely with S. 

 communis, but even here the agreement was not com- 

 plete. Apparently, Benecke did not find any specific 

 stimulus which would induce conjugation unless the 

 absence of ammonium salts be taken as such. Dan- 

 forth also found that some species of Spiro- 

 gyra did not respond by vegetative growth 

 as did others when NH 4 N0 3 (Ammonium ni- 

 trate) was added to the media. Spirogyra stetiformis 



