94 BRAUN, ON UNICELLULAR ALG^. 



ducing-, from a single motlier-cell, secondary, tertiary, and 

 quaternary, &c., cells up to a certain stage ; whilst the latter, 

 formed, as it were, from sister-cells, and never producing any 

 oifspring admitted into the society, might rather be termed 

 ccenobia. One exception to this rule only is known to the 

 author, presented in Sciadiimi, a strictly unicellular plant, but 

 which is nevertheless evolved into a true family, formed, 

 however, not by vegetative multiplication, but by way of 

 propagation. 



The author, therefore, from the foregoing considerations, 

 would classify the associations of the lower Algce, according 

 to their principal diflFerences, in the following manner : 



A. An association evolved by successive generations of cells from a single 



mother-cell (spore, (/onidium) : Familia ; 



a. Cells arising by vegetative division (more or less distinct, bvit retained 



in connection by means of the parent membrane) : the family repre- 

 senting an individual biologically single (a thallus broken up) : 



a. Order of cells immutable : Hormospora ! Fctlmodactylon ! Merismo- 



peedia ! Tetraspora, Glaocapsa, Glceocystis ; 

 (3. Order mutable : Nephrocijtium, Gltsoihece, Aplmnothece, Apioci/siis. 



h. Cells arising by true propagation : Familia c^nobiotica, composed 

 of individuals really distinct : Sciadium. 



B. Association constituted of several cells {gonidid) originally distinct : 



C^NOBIUM ; 



u. Constituted of zoogonidia, which become united after a motile stage, 

 and grow into immotile cells ; 



a. Order immutable : Ilydrodidyon ; 

 (i. Order mutable : Fediastrum. 



b. Of immotile gonidia, which grow into immotile cells ; 

 «. Order immutable : Scenedesmus, Sorastrum; 



ji. Order mutable : Ccelesirum ? 

 e. Of immotile gonidia, which change into vibratory cells ; 

 a. Order immutable : Gonium, Stephanosphcera, Synaphia ; 

 (3. Order mutable : Pandorina. 



To this arrangement another is subjoined, in which a 

 synoptical comparative view is given of the differences exhi- 

 bited in the lower Algce, derived from the simple or multiple 

 generation of cells described above ; 



A, MoNOCYTiDE^, or Uuicellularcs,. exhibiting a unicellular vital cycle : 



a. True, or unicellular in the strictest sense of the term ; no transitional 

 generations of gonidia ; 



«. Eremohi(B, growing with a solitary cell : Protococcus, Nag., Hydro- 

 cytium, Codiolim, Ophiocy Hum, Poly edrium !' {Chytridmm) ; 



