CONJUGATION OF FILAMENTOUS DESMIDIACE^. 275 



Fig. 76. 



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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 tuhe, uniting the 

 cavities of the two cells (Fig. 

 77, D, e). Through this tuhe 

 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 

 Conjugatem (§ 199). The 

 joint which contains the 

 sporangium can scarcely be 

 distinguished at first (after 

 the separation of the empty 

 cell), save by the greater 

 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 Olosterium ; 



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- 



dosUrium striatolu/m : — a, ordinary frond ; B, 

 empty frond ; c, two fronds in conjugation. 



FlO. 77. 



Didymoprtum GreiiQlii :—a^ portion of filament, surrounded by gelatinous envelope; a, dividing 

 joint; 0, single joint viewed transversely ; D, two cells in conjugation ; e, formation of sporangium. 



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



