MULTIPLICATION AND GENERATION OF DESMIDIACE.E. 265 



further and further from each other. This is a very different mode 

 of increase from that of the Conferracece , in which the terminal 

 cell alone undergoes subdivision (§ 249), and is consequently the 

 last formed. 



204. Although it is probable that the Desmidiacece generally mul- 

 tiply themselves also by the subdivision of their endochrome into a 

 number of Zoospores, only one undoubted case of the kind has yet 

 been recorded (the Pediastrece, § 218, being no longer ranked 

 within this group) ; that, namely, of Docidium Ehrenbergii, whose 

 elongated cell puts forth from the vicinity of the sutural line one, 

 two, or three tubular extensions resembling the finger of a glove, 

 through which there pass out from 20 to 50 motile Micro-gonidia 

 formed by the breaking-up of the endochrome of the neighbouring 

 portion of each segment.* 



205. Whether there is in this group anything that corresponds 

 to the Encysting process (§ 188) or the formation of Stato-spores, 

 (§ 197) in other Protophytes, has not yet been certainly ascer- 

 tained ; but the following observations may have reference to such 

 a condition. It is stated by Focke that the entire endochrome of 

 Closterium sometimes retracts itself from the cell-wall, and breaks 

 itself up into a number of globules, every one of which acquires a 

 very firm envelope. And it is affirmed by Mr. Jenner that "in 

 all the Desmidiacese, but especially in Closterium and Micrasterias, 

 small, compact, seed-like bodies of a blackish colour are at times 

 to be met with. Their situation is uncertain, and their number 

 varies from one to four. In their immediate neighbourhood the 

 endochrome is wanting, as if it had been required to form them ; 

 but in the rest of the frond it retains its usual colour and appear- 

 ance." It seems likely that, when thus enclosed in a fii-ru cyst, 

 the Gronidia are more capable of preserving their vitality, than 

 they are when destitute of such a protection ; and that in this 

 condition they may be taken-up and wafted through the air, so as 

 to convey the species into new localities. 



206. The proper Generative process in the Desmidiacece is 

 always accomplished by the act of Conjugation ; and this takes 

 place after a manner very different from that in which we have 

 seen it to occur in Palmoglcea (§ 186). For each cell here pos- 

 sesses, it will be recollected, a firm external envelope, which can- 

 not enter into coalescence with that of any other ; and this mem- 

 brane dehisces more or less completely, so as to separate each of 

 the conjugating cells into two valves (Fig. 113, c, D ; Fig. 114, c). 

 The contents of each cell, being thus set-free without (as it appears) 

 any distinct investment, blend with those of the other ; and a mass 

 is formed by their union, which soon acquires a truly membranous 

 envelope.f This envelope is at first very delicate, and is filled with 



* See Archer in " Quart. Journ. of Microsc. Sci.," Vol. viii. (I860), p. 227. 

 t In certain species of Closterium, as in many of the Diatomacece (§ 219), 

 the act of conjugation gives origin to two Sporangia. 



