THE FRESH-WATER ALGAE 



143 



65 (66) Chromatophore an axial plate, with several pyxenoids. Zygospore 

 lens-shaped or flattened and angled, in the conjugating tube. 



Mougeotia Wittrock. 

 Conjugation ladder-like or between two adjoining cells of the same filament. Zygospore in 

 the inflated conjugating tube, separated from the conjugating cells by two or more transverse 

 walls. 



Fig. 140. Mougeotia sp. «. showing the surface of the chlorophyll plate, b. showing the edge of the 

 chlorophyll plate. X about 500. (Original.) 



66 (65) Vegetative portion as in Mougeotia but zygospore not known. 



Gonatonema Wittrock. 



Aplanospores produced between two transverse mem- 

 branes near the center of an elongated cell. Spore 

 membrane double. 



Fig. 141. Gonatonema ventrkosum Wittrock. X 2S0. 

 (After West.) 



67 (2) Plants unicellular or of few cells. Chromatophore one or more 



parietal bodies, rarely central ; . . 68 



68 (190, 249) Plants unicellular, or of few cells united into minute families; 



frequently imbedded in gelatinous substance. 



Order Protococcales . . 69 



Each cell carries on all functions independently, and complexes may be regarded as an aggre- 

 gate of individuals. 



Three forms of reproduction may occur: i, purely vegetative; 2, by asexual zoospores; 

 3, by isogametes. More than one method frequently occurs in one species; the vegetative 

 reproduction may be by simple fission or internal division. 



69 (89) Vegetative cells or colonies for a portion or the whole of their exist- 



ence motile Family Volvocaceae . . 70 



70 (77) Cells single or in clusters, not forming a definite colony 71 



f I (72) Cells spindle-shaped; chromatophores several, indefinite, with two or 

 more pyrenoids and a pigment spot. 



Chlorogonium Ehrenberg. 



Cells with two cilia; membrane very thin, pigment spot in 

 anterior part. Numerous vacuoles and several pyrenoids present. 

 Division transverse. Reproduction by isogametes. Wille makes 

 this genus a section under Chlamydomonas. 



Fig. 142. Chlorogonium euchlorum Ehrenberg. a. a cluster of 

 X about 300. (After Ehrenberg.) i. single cell. (After Stein 



a cluster of cells. 



