10. Cells not showing H-shaped sections upon dissociation; pyrenoids present; 

 sexual reproduction known ..._H 



11. Cells coenocytic, cylindrical, with thick walls; chloroplast a dense, parietal 

 net with pyrenoids at the intersections of the meshwork, or with many 

 ovoid parietal discs; walls without ring-Hke scars at the anterior end of 

 the cells. cladophorales (in part) 



11. Cells not coenocytic, cylindrical but usually perceptibly larger at the an- 

 terior end, which is ordinarily marked by one or more ring-like scars 

 resulting from cell division; chloroplast a parietal net; reproduction 



oogamous, the female cells in the filament appearing swollen 



OEDOGONiALES (in part) 



12. Plant an expanded plate or tubular strand formed by several series of cells; 

 chloroplast a parietal plate similar to that in the Ulotrichales 'ulvales 



12. Plant an expanded sheet, composed of several series of cells; chloroplast a 

 stellate, axial body "schizogoniales 



13. Filaments composed of cylindrical or rectangular, uninucleate cells which 

 have a single, plate-Uke and parietal chloroplast; branches terminating in 

 setae, or with cell walls bearing hairs or bristles which usually are not 

 distinctly bulbous at the base chaetophorales 



13. Filaments not as above 14 



14. Filaments composed of cylindrical, coenocytic cells which may become 



attenuated toward their apices; setae and bristles wanting 



cladophorales ( in part) 



14. Filaments composed of cells which are larger at the anterior end; bearing 

 setae with much-enlarged, bulbous bases; reproduction oogamous, the 



female gametes produced in conspicuously swollen gametangia _ 



OEDOGONIALES ( in part ) 



15. Plant composed of long, branched coenocytic strands without cross walls 

 except where reproductive structures are cut off siphonales 



15. Plant a single cell, or a colony of definite or indefinite form; cells various 

 in shape, spherical, pyramidal, or polygonal, incapable of division in the 

 vegetative state; reproduction by autospores, zoospores, or isogametes. 

 (Compare with Tetrasporales, in which Chlamydomonas-like cells form 

 colonies in mucilage that resemble some members of this order.) 



CHLOROCOCCALES 



ORDER VOLVOCALES 

 In this order both vegetative and reproductive cells are motile. 

 The prototype of the Chlorophyceae is to be found among the 

 1-celled members, from which colonial Volvocales, as well as other 

 orders of green algae, are thought to have evolved. There may be 

 2, 4, or rarely 8 flagella. Usually there is a conspicuous pigment-spot. 

 Although a few colorless forms are recognized, by far the majority 

 of these organisms have a cup-shaped, parietal chloroplast (rarely 

 stellate or axial) with one or more pyrenoids. Reproduction is by 

 cell division, by zoospores (formed 2—8 in a cell), by isogametes, 

 or by heterogametes, egg and antherozoids being formed in sexual 

 reproduction among the more advanced colonial genera. 



[67] 



