492 BOTANICAL GAZETTE [june 



own experiments and is so exceedingly rare in the work of others, 



he thinks it must be considered a very unusual abnormality. 



York (33), who worked several years on the sexuality of Spirogyra, 



seeking methods for determining the sex before conjugation, says 



"zygotes were never found in both filaments, but only in the one 



containing the greater amount of food. The male and female are 



morphologically and physiologically different." 



Summarizing, it appears that the evidence for bisexuality is 



based (1) upon work done over 100 years ago, when the importance 



of cross-conjugation was not realized, and has not been verified 



since; (2) upon lateral conjugation, a strong basis ignored by the 



unisexualists; (3) upon the chance observations of Cleve, Bessey, 



and West. At this point it is interesting to note that Hassall 



figures no species in cross-conjugation that was thus figured by 



Vaucher; that Bessey's species is not that of either Hassall or 



Vaucher; and that the one cited by West is still different. Thus 



these would all appear to be abnormalities. 



On the other hand, the advocates of unisexuality urge (1) that 

 Klebs found that a filament would not conjugate with itself, hence 

 it is of one sex; (2) that the work of Vaucher needs verification; 

 (3) that the figures of Hassall may have been taken from older 

 works; (4) that, since the species figured by Vaucher and Hassall 

 are common, the phenomenon should have been observed by 

 modern investigators; (5) that specialists have seen but few cases, 

 not more than a dozen, and these have been called abnormalities 

 because of their rareness; (6) that experimentalists who have 

 spent years on the sexuality and abnormal conjugation of Spirogyra 

 have not observed cross-conjugation. All these things point to 

 the unisexuality of the filament. 



If, how r ever, as stated in the beginning of this paper, a true 

 case of cross-conjugation of Spirogyra should occur normally to 

 any extent, it would settle the question, for one species at least. 

 A species in this condition was found by the author while making a 

 collection of algae along a stream near Durham, North Carolina, on 

 April 1, 19 1 5. The water stood in pools on the low ground, and 

 it was from one of these pools that the collection was made. There 

 was comparatively little of this species mixed with a larger Spiro- 



