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 J). 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, 

 Penium didymocarpum Luiid. ; D, conjugation of four individuals just produced by division ; 

 E, completed conjugation showing the double zygospore, x 464. F, Closteriiirn 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 conj ugation-tube is developed (fig. 235 J). 

 The two conjugating cells, which are sexually indistinguishable, approximate 

 and usually become enveloped in mucus. In the Cosmariese 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 



