



498 BOTANICAL GAZETTE [june 



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which the writer has observed but not diagrammed, since cases in 

 which there are more than 4 consecutive zygotes or empty cells show 

 that division has occurred once or more after reduction. Here, 

 then, is a distinct and characteristic difference between lateral 

 and cross-conjugation. In lateral conjugation there can be no 

 further cell division after reduction is complete, but in cross- 

 conjugating filaments there may be. A study of the plates shows 

 that in the case of fig. 2, pi. XXV, division must have occurred 3 

 times subsequent to reduction in part of the cells at least, in order 

 to produce the 1 1 consecutive males there shown. 



From the foregoing it would seem that the phenomenon of 

 cross-conjugation lies between lateral and scalariform and partakes 

 of some of the characters of each. Like the former, the reduction 

 does not occur in the zygote, but is retarded, and none of the poten- 

 tial gametes is lost. Like the latter, division continues after 

 reduction has taken place. For these reasons it would seem that 

 the filament of Spirogyra, in this species and in those with lateral 

 conjugation at least, must be homologized with the sporophyte 

 of higher plants. With these facts as a basis, the following con- 

 clusions seem to be justified: 



1. Bisexuality of the filament does occur in certain species of 



Spirogyra, but not necessarily in all species. 



2. Reduction may occur in the zygote, in which case a filament 

 wholly of one sex arises, or reduction may occur just previous to 

 reproduction, in which case none of the nuclei degenerates, and 

 filaments of a bisexual nature are produced, which would conjugate 

 either laterally or by cross-conjugation. 



3. Cell division may take place subsequent to reduction, some 

 cases showing 3 divisions, and this is an essential difference between 

 lateral and cross-conjugation, since the latter may continue cell 

 division after reduction is complete but the former apparently 

 does not. 



4. The filament of Spirogyra, in this species and those with 

 lateral conjugation, is homologous with the sporophyte of higher 

 plants. 



Trinity College 

 Durham, N.C. 



