58 MISSOURI BOTANICAL GARDEN 



b 



periment 



many of those in the tap water had also germinated. In 

 like manner when conjugating material of the same species, 

 but from a different locality, was placed in solutions Nos. 3 

 and 4 of Benecke's second series and also in tap water, dis- 

 tilled water, and a solution containing .008% NH 4 N0 8 there 

 was, at the end of four weeks, more or less germination of 

 zygospores in each case, although to a less extent in the tap 

 water and distilled water. With the other species a similar 

 germination did not seem to occur. Whether or not S. 

 dubia germinated in nature at this time could not be satis- 

 factorily determined, for while no filaments were seen it may 

 have been because they were eaten by the large number of 

 tadpoles that appeared in the ponds. 



Briefly to summarize the results obtained, it appears that 

 there are specific differences as regards the reactions of fila- 

 ments and zygospores in the species studied, and that Ben- 

 ecke's conclusions, based on the reactions of S. communis, 

 are probably not of general application, or are applicable 

 only under very special conditions. Of the five species inves- 

 tigated three failed entirely to give the expected results, and 

 a fourth failed in every case but one. The remaining species, 

 S. Grevilleana, seems to agree more closely with S. communis 

 but even here the agreement is not complete. The existence 

 of sexual strains, such as occur in some of the moulds, seems 

 to be suggested, but evidence on this point is lacking. 



When Benecke's results are analyzed it becomes apparent 

 that he did not find any specific stimulus that would induce 

 conjugation unless the absence of ammonium salts be taken 

 as such. The foregoing observation seems to show very clearly 

 that in many cases at least the absence of these salts is not 

 enough to bring about conjugation. Hence it seems all the 

 more probable that, as Fritsch and Rich have stated, the con- 

 ditions governing conjugation in this genus are very com- 

 plicated and probably not always of such simple nature as 

 Benecke is inclined to believe. 



is inclined to believe. Indeed it is still possible that 

 Spirogyra like Dictyota is inherently periodic in its func- 



