THE GREEN ALGAE OF NORTH AMERICA 23 



Differs from Volvox in the absence of protoplasmic connec- 

 tion between the cells, and in that the differentiation of vegeta- 

 tive and gonidial cells does not occur in a colony until it is 

 freed from the mother colony. From Pleodorina it differs in 

 having vegetative and gonidial cells intermingled, not developed 

 in separate areas. 



B. POWERSII Shaw, 1916, p. 254. Mature colony 1800-2500 

 It. diam., usually about 2000 /* ; vegetative cells about 12 /x diam., 

 distant 50-250^; gonidia 10-78 in number ; new colonies less 

 than 150/11 diam. when leaving mother colony, differentiation 

 occurring later.* 



Page 135, for generic and specific account of VOLVOX, 

 substitute, 



Colonies spherical or ovoid, of 200-20,000 cells or even more ; 

 cells pyriform, in most species united by protoplasmic threads, 

 and closely set near the surface of the colony, the cilia pro- 

 jecting. A number of cells are specialized as parlhenogonidia, 

 asexually forming new colonies by repeated division. Sexual 

 reproduction by antheridia and oogonia ; the former containing 

 8-256 clavate antherozoids, with red stigma and two cilia ; 

 oospores round, with smooth or stellate membrane ; new colo- 

 nies formed by their germination, in the same way as by 

 parthenogonidia. 



Powers, 1907 & 1908, gives results of the author's studies of 

 the genus, leading to the belief that it is impossible to include 

 all our American forms under the European species, V.globator 

 and V. aureus ; indeed he found no plants agreeing with either 

 of those species. Only long-continued observations in many 

 localities can determine whether Powers' new species will be 

 maintained, but the following notes indicate the diagnostic 

 characters as far as possible ; the author does not give as full 

 comparative diagnoses as might be wished ; for details the two 

 papers should be consulted ; the "second form " Powers, 1907, 

 appears now as Besseyosphaera Shaw.t 



*The wording is somewhat changed from the author's description, 

 which is curiously zoological for a botanical subject. " Daughters less 

 than 150 fa diam. at birth." Figures of this species from photomicro- 

 graphs were given by Powers, 1907, but they are very unsatisfactory, and 

 as no fresh material is available, no figures are given with this paper. 



tPowers' papers appeared in a publication containing little botanical 

 matter; indeed he refers to his species, 1908, p. 142, as part of "our 

 fauna ", and they have not attracted the attention they deserve, whether 

 their conclusions are fully accepted or not. 



