172 



STRUCTURAL BOTANY 



only to the receptive partner. If this be so, it points 

 to a certain degree of sexual differentiation. 



That there is actually a certain distinction of sex in 

 Spirogyra is evident from the fact that all the cells of 

 each conjugating filament usually behave in the same 

 way, either giving up their own protoplasm or receiving 

 that of the fellow-filament. That the difference, how- 

 ever, is not fixed is shown by the fact that conjugation 

 sometimes takes place monceciously, i.e. between the 

 cells of the same filament. This mode of union is called 



" chain-like" in opposition to 



the more usual dioecious or 

 " ladder-like " method, and both 

 processes may occur in the 

 same species. In monoecious 

 conjugation two adjoining cells 

 put out very short lateral 

 processes, which arise close to- 

 gether, on either side of the 

 transverse wall separating the 

 two cells. The processes unite, 

 and the contents of the one 



FIG. 73. Conjugation more 

 advanced. At a the proto- 

 plasm is in the act of passing 

 over ; at b the union is com- 

 plete, one cell having trans- 

 ferred all its contents to the 

 other. Magnified about 350. 

 (After Sachs.) 



cell pass through the side passage and fuse with those of 

 its neighbour. In this case there may be a certain 

 sexual difference among the individual cells, but the 

 filament is obviously bisexual 



In most of the allies of Spirogyra (e.g. in the Desmids) 

 there is no trace of any difference of sex, for the cell- 

 contents meet and fuse midway between the parent cells, 

 each of which thus takes an equal part in the process. 



The contents of the zygospore assume a darker colour, 

 and the starch disappears, giving place to oil, which 

 constitutes the reserve carbonaceous material during the 



