CONJUGATION OF FILAMENTOUS D E S M ID I A C E^E. 275 



FIG. 76. 



jugation, the outer cell-wall of each splits or gapes at that part 



which adjoins the other cell, 



and a new growth takes 



place, which forms a sort of 



connecting tube, uniting the 



cavities of the two cells (Fig. 



77, D, E). Through this tube 



the entire endochrome of 



one cell passes over into the 



cavity of the other (D), and 



the two are commingled so 



as to form a single mass (E), 



as is the case in many of the 



Conjugates ( 199). The 



joint which contains the 



sporangium can scarcely be 



distinguished at first (after 



the Separation Of the empty Closlenum s triatolum. A , ordinary frond; B, 

 Cell), Save by the greater empty frond ; c, two fronds in conjugation. 



density of its contents ; but 



the proper coats of the sporangium gradually become more dis- 

 tinct, and the enveloping cell-wall disappears. The subsequent 

 history of the sporangia is still obscure ; since, although it can- 

 not be doubted that they give origin to new plants resembling 

 those by whose conjugation they are formed, it is not known 

 whether each sporangium in the first instance developes a single 

 cell, or a brood of cells. The latter seems, from the observa- 

 tions of Jenner and Focke, to be the case with Closterium ; 



whilst those of Mrs. H. Tho- 

 mas (loc. cit.) indicate that it is 

 likewise in Cosmarium, whose 

 sporangium has been seen by 

 her to emit large numbers of 

 bodies resembling zoospores. 

 This part of the history of 

 the group is yet involved in 

 much mystery ; more espe- 



FIG. 77. 



Didymoprium Grevillii: Apportion of filament, surrounded by gelatinous envelope; B, dividing 

 joint; c, single joint viewed transversely ; D, two cells in conjugation ; E, formation of sporangium. 



cially since, according to the observations of Mr. Ralfs, there 



