SPIROGYRA. 91 



conjugate assume a position parallel to one another, and 

 on them the following observations are to be made , 



1. Cells opposite one another put out rounded 

 processes which meet. 



2. The wall at the point of junction is absorbed, and 

 thus the canal of communication is formed. 



3. Meanwhile the protoplasm of the two cells has 

 rounded off, one (the male) usually doing so earlier than 

 the other (the female). 



4. The protoplasm of the male cell passes through the 

 canal, and coalesces with the female to form the zygote. 



5. The zygote surrounds itself with a thick stratified 

 cell- wall, which is smooth or shows various markings of 

 the surface according to species. 



By fixing material in course of conjugation and staining with 

 hsematoxylin, Schmitz has been able to observe that the nuclei 

 of the conjugating cells coalesce to form the single nucleus of the 

 zygospore. 



For comparison with Spirogyra observations should 

 be made on Mesocarpus, a filamentous fresh-water Alga, 

 having in each cell a single straight flattened chromato- 

 phore, in a central position. The conjugation differs 

 from that of Spirogyra in two points: (1) that the 

 zygospore is formed in the conjugation-canal, and not 

 in the cavity of one of the conjugating cells ; (2) that 

 a part only of the protoplasm of the conjugating cells 

 is used up in forming the zygospore. 



DESMIDIE.E. 



Members of the closely-allied group of the Desmidieoe 

 should also be examined; e.g. species of Closterium, 



