172 



STRUCTURAL BOTANY 



only to the receptive partner. This fact 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 monoeciously, 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 



73. Conjugation more put out very short lateral 

 advanced. At a the proto- i i i 



plasm is in the act of pissing processes, which arise close to- 

 over ; at b the union is com- gether, on either side of the 



plete, one cell having trans- ,, .. ., 



ferred all its contents to the transverse wall separating the 

 other. Magnified about 350. two cells. The processes unite, 



(After Sachs.) 



and the contents of the one 



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 Spiroyyra (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 



