THE FRESH-WATER ALGAE 



153 



135 (133, 134, 136) Characteristics as in Pleurococcus, but sometimes forming 

 short filaments Pseudo-pleurococcus Snow. 



This form may remain indefinitely in either 

 a filamentous or unicellular state according 

 to the conditions in the environment. In 

 the filamentous state it resembles a small 

 form of Stigeoclonium, but is distinguished 

 from it by the absence of zoospores. 



Chodat regards a form similar to this as 

 a true Pleurococcus and believes that short 

 filaments are characteristic of that genus. 



FIG. 176. Pseudo-pleurococcus vulgaris Snow. 

 X 600. (Original.) 



J 36 (133, 134, 135) Reproduction by fission in three directions and by inter- 

 nal division . . Palmellococcus Chodat. 



Chromatophore a parietal plate, without a pyrenoid. In addition to reproduction by fission 

 and internal division, a rejuvenescence of the cell contents may occur, accompanied by a cast- 

 ing off of the mother-membrane. An orange-red oil is sometimes present. 



137 (i3 2 > I 55> I 74) Reproduction by'internal division only. 



Family CHLORELLACEAE . . 138 



138 (142, 151) Cells spherical, ellipsoidal, or irregular. Membrane 



smooth 139 



139 (140, 141) Cells spherical; chromatophore a single, hollow sphere with 



one pyrenoid Chlorella Beyerinck. 



Cells spherical or somewhat elongated; chromatophore lining the mem- 

 brane, open on one side, with a single pyrenoid. 



The name Zoochlorella Brandt has been given to this same genus and ante- 

 dates the name of Chlorella by some years, but the name Chloretta seems 

 more appropriate. 



FIG. 177- Chlorella sp. X 600. (Original.) 



Cells spherical, chromatophore of many parietal discs, each 

 with a pyrenoid Eremosphaera de Bary. 



Size relatively large; chromatophores many, parietal; nucleus 

 prominent. Reproduction by internal division. 



The cells are large, spherical, and conspicuous. The nucleus is 

 distinct, suspended in the middle of the cell by strands of proto- 

 plasm. Two or four daughter individuals may originate by succes- 

 sive division of the contents and are liberated by the rupturing of 

 the mother membrane. Eremosphaera is almost constantly found 

 among Desmids in Sphagnum swamps. 



FIG. 178. Eremosphaera viridis de Bary. X 125. (Original.) 



Cells spherical or irregular; chromatophores many, angular, 

 radially arranged; many pyrenoids in each. 



Excentrosphaera Moore. 



Plant consisting of a single cell, in mature condition varying 

 in outline from spherical and elliptical to irregular and eccentric 

 forms. Chromatophores large, angular, usually radiately ar- 

 ranged, closely lining the wall. Pyrenoids minute, numerous in 

 each chromatophore. Multiplication by non-motile spores 

 (aplanospores) which escape by the dissolution of a part of 



the cell wall. Reaction to all external stimuli negative. 



FIG. 179. Excentrosphaera viridis Moore. X 160. (After Moore.) 



142 (138, 151) Cells spherical or elongated, membrane with hairs, spines, or 

 reticulate markings 143 



140 (139, 141) 



HO) 



