1917] CUNNINGHAM— SEXUALITY OF SPIROGYRA 



493 



gyra and some germinating Vaucheria. The phenomenon of cross- 

 conjugation was not observed until the material had been brought 

 into the laboratory, and heavy freshets prevented further collection. 

 However, from this interwoven mass, not larger than a pea, more 

 than 70 slides have been prepared showing cross-conjugation. 

 Some of the slides have several distinct pairs of filaments in this 

 condition. Considerable effort was made to secure long filaments, 

 but this was unsuccessful on account of the intricate tangling of 

 the mass. This species was again collected early in April 1916, in 

 approximately the same locality, showing essentially the same 

 phenomena as the earlier collection, but, owing probably to defi- 

 cient rainfall, was not abundant and hence it was not possible to 

 add any important facts not shown by the material gathered the 

 year before. 



A careful investigation of the material shows that all the known 

 forms of reproduction in Spirogyra are represented in this species. 

 While aplanospores occur, they are not found frequently, and they 

 are hard to identify. The regular zygotes are formed by 3 distinct 

 methods. The most common is the well known scalariform method, 

 in which the 2 conjugating filaments have the appearance of a 

 ladder, and the gametes travel in only one direction, so that one 

 filament contains all the zygotes. This has been followed for 

 20 to 25 pairs of conjugating cells. Zygotes are formed also by 

 lateral conjugation, the contents of one cell passing into the adjoin- 

 ing cell of the same filament. This is accomplished in this species 

 by the bulging of the cell wall away from the septum at one side 

 until there is a small opening left between the 2 cells through which 

 the contents pass. In general appearance the zygotes are like 

 those formed by scalariform conjugation. Usually the cells 

 follow the law laid down by Hassall (16, p. 34) that 2 males 

 alternate with 2 females. This applies only to those filaments in 

 which lateral conjugation occurs alone. In this species it is 

 frequently accompanied by genuflexions. This method (lateral 

 conjugation) occurs in filaments that are also conjugating in the 

 usual scalariform manner. Zvgotes are further formed by true 



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