PERIODICITY IN SPIROGYRA. 



53 



The exact formulae given were departed from to the extent 

 of substituting distilled water for tap water, the composition 

 of the latter being unknown. With Benecke No. 3 gave good 



but 



case, 



many 



and apparently grew to a slight extent, no conjugation took 

 place during the five w T eeks in which the solutions remained 

 unchanged. Januai 

 these cultures. The 



some melted 



The filaments in solution No. 4 died during 

 February, those in No. 3 persisted until April. There was 

 no conjugation in either. In regard to the several cultures 

 started December 10 it is of interest to note that those in tap 

 and distilled water died, as did also several cultures in which 

 NH 4 N0 3 alone was added to the water, while the more elab- 

 orate media proved favorable. No. 5 of the second. series, here 

 as elsewhere, appeared to be slightly toxic, probably due to 

 the FeS0 4 contained. It may be remarked at this point that 

 S. setiformis has not seemed to respond to NH 4 NO a by vege- 

 tative growth as have S. dubia and S. longata. It died in the 

 above mentioned solutions and when a slight trace was added 



months 



became gnarled 



perfect 



formis was used may be 



mentioned. 



March 



ma 



terial had been left in the fall and by the first of April the 



majority of the hlaments were trom lo mm. to 20 mm. in 

 length. All the different salt solutions w T hich Benecke had 

 found to favor or permit conjugation in S. communis were 

 made up according to his formulae except that in place of 

 the occasional pond or tap water 100 cc. of twice distilled wa- 

 ter that had been further treated with iron hvdrate was used 

 in each case. April 5 a few filaments were placed in each 

 of these media and kept in the comparatively uniform tem- 

 perature and good illumination of the laboratory. April 19, 

 when filaments of the original stock had about doubled in 



length, only one or two of these cultures show T ed any growth 



