PERIODICITY IN SPIBOGYRA. 51 





conjugation results not so much from external as from 



internal conditions." 



somewhat 



( 



This in- 



cornmunis in different media 



ter or salt solutions) in aquaria of various sizes. They were 



most part placed in bright 

 i ransriner from 12 deerees tc 



He 



as his tabulated data show, that in nitrogen-free solutions 

 conjugation took place in a short time. The number of 



somewhat 



media, distilled water being 



If 



parallel cultures were run in which — NH 4 or -N0 3 had 

 been added in appropriate amounts (about .05%) to any of 

 the above media or substituted for one of the constituent 

 salts, no conjugation took place at all but generally a good 

 vegetative growth ensued. As a result of his work Benecke 

 believes that conjugation in Spirogyra is due to the failure 

 of ammonium salts which he supposes to be removed from 

 the water by angiosperms which increase in size and abund- 



1 



ance as the season advances. 



Benecke's work seeming to be of a very definite character, 

 an attempt was made by the writer during the winter of 

 1909-1910 to repeat these experiments using other species 

 in the place of S. communis. The result has been almost a 

 complete lack of conformity in so far as the question of 

 zygospore formation is concerned. The stimulating effect 

 of an ammonium salt on growth, however, frequently proved 

 to be quite as marked as it was with S. communis in 

 Benecke's cultures. The species used for the present study 

 were chiefly 8. setiformis, S. longata, S. Grevilleana, S. dubia, 

 and S. porticalis. There was also a large and very resistant 

 form which occurred for the most part as scattered filaments 

 associated with the other species and generally persisting in 

 the aquaria after the associates had died. Unfortunately S. 

 communis w T as not accessible. 



In the fall, S. setiformis was the most available form. It 



was found in considerable abundance in one of the small, 



