24 SURVEY OF THE REPRODUCTIVE PROCESS 



with the endochrome, which escapes in a similar way from 

 a neighbouring cell, the two plastic masses unite by the 

 deliquescence at the meeeting point of their imperfect walls 

 and become fused into a single spore, the investment of 

 which subsequently acquires the character of a true cellulose 

 membrane.* 



The variations of the process in different cases appear to 

 depend very much on the mode of dehiscence of the original 

 cells. In Desmidiese, in which the cells generally isolated 

 are marked by a median constriction, each of the pairs 

 of cells concurring in the process of reproduction splits into 

 two, and the effused contents comingling in the void space 

 surrounded by the four empty valves, are there developed 

 into a germ mass, whose investing layer acquires subse- 

 quently a cellulose character, and usually becomes covered 

 also with siliceous spines. 



In Diatomacese the pair of conjugating frustules first be- 

 come embedded in a mass of gelatine, and then the valves of 

 each separate as if hinged at one side, so as to form fissures 

 along their contiguous margins, through which the contents 

 escape, and become amalgamated in the gelatinous matrix. 

 Two sporoid bodies are generally produced, f owing, there 

 is reason to believe, to a sub-division of the original germ- 

 mass. They appear as a pair of new frustules lying cross- 

 wise to the original ones, and of much larger dimensions. J 



In Meloseira a somewhat analogous kind of action seems 

 to take place between the ends of a single cell the cell 

 being an elongated cavity, apparently formed by the fusion 

 of two or three into one. 



In the confervoid filamentous Algae, Dr. Carpenter gives 



* Hoffineister Annals of Nat. Hist., 3d ser. I. 1. 

 f Thwaites in Ann. Nat. Hist., XX. pp. 9 and 343. In Fragillario, 

 however, there is bnt a single spore. 



J Thwaites in Ann. Nat. Hist. 2d Ser., I. 166. 

 J. H. Carter in Ann., 2d Ser., XVII. 1. 



