90 



TRANSLATIONS. 



Algarum Unicellularium Genera nova et mimis cognita, 

 preemissis Observationibus de Algis Unicellularibus 

 in genere. 



New and less known Genera of Unicellular Algj5, preceded 

 by Observations respecting Unicellular Alg^ in general. 

 By Alex. Braun. (Lipsiae, 1855 ; with six Plates.) 



Continued from No. XVII, p. 16. 



In one respect only does tlie question appear to require 

 more strict definition, a careful distinction should be made 

 between Algoi which are unicellular only in the looser sense 

 of the term, and those which have a more direct title to the 

 name ; for several genera of Alga (among the Palmellacece, 

 Desmidiacece, and Diatomacea) , though formed indeed of 

 isolated cells, or of cells loosely connected merely by a gela- 

 tinous matter, nevertheless exhibit a vegetative di\dsion of 

 the cells, by means of which they are multiplied through a 

 more or less extended series of generations, until the cycle of 

 vegetation terminates in the production of gonidia or of 

 spores. In these genera, therefore, as in the multicellular 

 Algce, divers generations of cells are to be distingu.ished : — 

 1, ordinal* which by their conjunction constitute the vege- 

 tating individual, either continuous, or broken up and dis- 

 sected into parts (individuals of a lower order) ; and 2, car- 

 dinal,^ by which fructification is accomplished, and the tran- 

 sition to a new series of ordinal cells effected. It is obvious, 

 therefore, that Alga of this kind, since they really pass 

 through a multicellular vital cycle, and are unicellular only 

 in appearance (pseudo-uniceUular), must, in a biological 

 sense, be regarded as multicellular ; whence it is readily seen 

 that they cannot be separated from other multicellular Alga 

 formed of contiguous cells, by any strict line of demarcation 

 either morphological f or systematic. § Unicellular Alga, in 



* ' Rcihengcncrationen,' Niisr. eiiiz. Algen, p. 25. 



t ' Uebergangsgcneratioii,' ibid. (Schlussgcneration). 



X Compare i\\e Dlatomacea; and 5o\\iav^ Desmidiacefe with, the catenated 

 forms : Tetmspom with the Ulv^e, tlirough T. bullosa, which is referred by 

 Thurct to the Ulvacem, under the name of Monotrema ; compare also Hor- 

 mospora with Ulotriche, Slichococcus with Uormidium, Synechococcus with 

 Oscillaria, &c. 



§ The Diatomacem and Desmidiace/r, placed, according to Nageli's elassi- 



