BRAUN, ON UNICELLULAR ALG.E. 91 



tlie wider sense of the term, would be distinguished by a 

 more essential character, if with them were conjoined all 

 those which exhibit similar generations of cells, so that a spe- 

 cific idea is equally represented^ in each cell, either free or 

 united with others. But such a character, if the matter be 

 more closely scrutinised, is scarcely anywhere really exhibited 

 among AlgcB endowed with the property of vegetative di\dsion, 

 since, at any rate, the cells of the cardinal generation differ 

 from the rest physiologically and sometimes also morpho- 

 logically; and in the cells themselves of the ordinal gene- 

 rations some differences, which can hardly be regarded as 

 fortuitous, and chiefly relating to magmtude,t may be ob- 

 served. It is obvious, therefore, that in all these instances a 

 specific idea can only be really completed by a certain cycle 

 of cells. 



The more strictly unicellular Algos, however, present con- 

 ditions altogether different, their entire and undivided -\-ital 

 cycle being completed by the continuous evolution of a single 

 cell. In them there is no division of the cell throughout the 

 whole course of vegetation, nor any multiplication and diver- 

 sity of generations, since the same cell successively assumes 

 the functions of thaUus and of organ of fructification (of gonio- 

 cyst or sporo-cyst, vuJg. " sporangiimi ") . But among these 

 also some diversity is presented, by which the forms, in the 

 strictest sense of the term, unicellular, are separated from 

 those which, in a certain sense, hold an ambiguous place ; for 

 the unicellular AJgce differ mth respect to the generation of 

 the gonidia, which in some is efFected by the direct separation 

 and transformation of the cell- contents, J and in others is 

 preceded by a previous repeated act of division. § That the 

 former are unicellular, in the strictest sense of the term, no 

 one will doubt, since they exhibit no series of generations 

 within the \ital cycle ; but the latter, which, after the uni- 

 cellular state of vegetation, pass through intermediate quasi 

 multicellular states, in order to complete their fructification, 

 might be regarded as multicellular Algcp, if indeed the term 

 cells could properly be applied to those transitory generations, 

 composed merely of portions of the plasma of the primary 



fication, amono^ the. unicellular Alga, are very closely allied to the Zygnema- 

 cea among the multicellular Alga ; and in tlie same way the Chroococcaceae 

 are intimately related to the Nosiochitiea (in the wider sense). 



* Nageli, einz. Alg., pp. 2 and 3. 



f Compare the Diatomacea and Desmidiacece (especially the Closteria), as 

 •well as the Glceocapsce, Tetranpora, &c. 



% As in Bydrocytium, Codiolum, Chytridium, Bryopsis, Botrydium, and 

 Hydrodietyon. 



§ lu Cystococcm, Characium, aud Pediastnm. 



VOL. V. I 



