GENERATION AND DEVELOPMENT OF DES3I1DIACE.E. 267 



the sporangia of Cosmariuni are transformed by repeated binary- 

 subdivisions into 8 or 16 cells, which assume the original form of the 

 parent before they are set free by the rupture or diffluence of the 

 wall of the sporangium. The observations of Jenner and Focke 

 render it probable that the same is the case in Closterium; but 

 much has still to be learned in regard to the development of the 

 products of the Generative process, a as it is by no means certain 



Fig. 114. 



Conjugation of Closterium striatolum : — a, ordinary frond; b, empty 

 frond ; c, two fronds in conjugation. 



that they always resemble the parent forms. For it is affirmed by 

 Mr. Ralfs that there are several Desmidiacese which never make 

 their appearance in the same pools for two years successively, 

 although their Sporangia are abundantly produced, — a circumstance 

 which would seem to indicate that their sporangia give origin to 

 some different forms. It is a subject, therefore, to which the 

 attention of Microscopists cannot be too sedulously directed. 



207. The subdivision of this Family into Genera, according to 

 the method of Mr. Ralfs ("British Desmidiese "), as modified by 

 Mr. Archer (Pritchard's " Infusoria"), is based in the first instance 

 upon the connection or disconnection of the individual cells ; two 

 groups being thus formed, of which one includes all the genera 

 whose cells, when multiplied by binary subdivision, remain united 

 into an elongated filament ; whilst the other comprehends all those 

 in which the cells become separated by the completion of the 

 fission. The further division of the filamentous group, in which 

 the Sporangia are always orbicular and smooth, is based on the 

 fact that in one set of genera the joints are many times longer 



