372 



Conjugate 



and with the solitary exception of Desmidium cylindricum, there is no definite 

 conjugation-tube. Except in Desmidium Baileyi, and to a much less-marked 

 degree in Desmidium Swartzii and D. aptogonum, all the filamentous Desmids 

 dissociate into individual cells prior to normal conjugation (consult fig. 233 C, 

 D and K ; and fig. 235 ./). Also, the zygospores are formed between the 

 gametangia (or conjugating cells) in all Desmids with the solitary exception 



Fig. 234. A C, three stages in the conjugation of Staurastrum Dickiei Ralfs, x 356. D and E, 

 Peniutn didymocarpum Lund. ; D, conjugation of four individuals just produced by division ; 

 E, completed conjugation showing the double zygospore, x 464. F, Closterium lineatum 

 Ehrenb., showing the double zygospore, x 100. z, zygospore. 



of Desmidium cylindricum Grev., in which the zygospore is formed within the 

 female gametangium and a distinct conjugation-tube is developed (fig. 235 </). 

 The two conjugating cells, which are sexually indistinguishable, approximate 

 and usually become enveloped in mucus. In the CosmarieaB the longitudinal 

 axis of one conjugating cell is very often at right-angles to that of the other 

 (fig. 234 A and B ; fig. 235 J) and at the commencement of conjugation the 

 semicells of each individual come apart at the isthmus. Each gamete issues 



