186 FRESH-WATER ALG^ OF THE UNITED STATES. 



Multiplication takes place by a vegetative division of the 

 cells; propagation by transitory goniclia arising by various 

 divisions of the protoplasm from the last vegetative generation ; 

 gonidia without integument, mostly furnished with two cilia at 

 the anterior end, and moving about actively. Rabenhorst. 



Genus 51, DICTYOSPHAEBIUM, Naeg. 



Cells green, egg or kidney-shaped, united into a somewhat 

 globose, hollow family, involved in a gelatinous, more or less 

 liquid tegument; sometimes wanting; swimming free. Cells 

 furnished with a single chlorophylous vesicle and a lateral trans- 

 parent spot, surrounded with thick coats which are confluent 

 into a homogeneous jelly ; united by very fine filament, which 

 are dichotomously divided and radiate from the center to the 

 peripheral families. Division of the cells occurring primarily 

 in all directions, later only radiately. 



* 



DlCTYOSPHAERIUM EHREXBERGIANUM, Naeg. 



Family subglobose or suboval ; cells somewhat ovate or 

 subglobose, with thin smooth membrane. 



Diameter of cells, 4-7 f*. 

 Diameter of family about 15-18 yw. 

 Not infrequent in ponds. 



Syn. Dictyo. pulchellum, Wood. 



A form not to be separated from Dictyo. Ehrenbergii, as 

 illustrated and described by Naegeli. It is indeed more like 

 the typical form than the plant which has frequently oc- 

 curred to me. 



Plate CLYI, figs. 29, 30, two families ; fig. 31, a family 

 after Naegeli' s figures. 



DlCTYOSPHAERIUM RENIFORME, Bulnh. 



Cells reniform, nearly twice as broad as long. Families 

 somewhat oval or irregular. 



Diameter of cells, 6-9 )JL by 10-20 ^ 

 Diameter of families, 40-70 ^. Very variable. 



Ponds, now and then. 

 Plate CLVI, fig. 28, a regularly shaped family. 



DlCTYOSPHAERIUM HlTCHCOCKII, Wolle. 



Cells green, broadly oval, nearly one-half longer than 

 broad ; often constricted in the middle indicating the pro- 



