446 PRACTICAL BOTANY 



7. The gradual formation of the septum, beginning 

 at the periphery and proceeding towards the centre. 



III. In summer or autumn the process of conjuga- 

 tion and formation of the zygospores may frequently be 

 observed in Spirogyra : filaments which are about to 

 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 specimens in course of conjugation and staining with 

 haematoxylin, Schmitz has been able to observe that the nuclei 

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

 zygospore, but according to recent observations this coalescence 

 only takes place after a considerable time, when the zygospore is 

 nearly mature. 



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 



