3. Cells solitary pleurochloridaceae (in part) 



3. Cells in clusters, colonial 8 



4. Cells cylindrical, growing by 



increasing in length* chlorotheciaceae (in part) 



4. Cells fusiform, ovate, globose, or subglobose, 



not growing in length characiopsidaceae 



5. Cells globose, several to many included 



in a gelatinous sheath gloeobotrydaceae (in part) 



5. Cells not inclosed in a gelatinous sheath, of various shapes 6 



6. Cells rectangular, or cylindrical ( usually elongate ) , 



growing by increasing in length _ .. 7 



6. Cells globose, ovate, triangular, or polyhedral, 



not increasing in length pleurochloridaceae (in part) 



7. Cells cylindrical, circinately 



coiled or S-shaped chlorotheciaceae (in part) 



7. Cells quadrate or, if cylindrical, straight 



or only slightly curved centritractaceae 



8. Cells compactly arranged, adjoining walls flattened 



by mutual compression -. botryochloridaceae 



8. Cells in colonies but not closely 



aggregated; walls not flattened gloeobotrydaceae (in part) 



FAMILY PLEUROCHLORIDACEAE 



Mostly solitary ( incidentally clustered because of autospore libera- 

 tion ) , mostly free-living cells of various shapes, globose, tetrahedral, 

 short-cylindric, or spindle-shaped, sometimes narrowly so and de- 

 cidedly needle-like; cells not growing in length; wall smooth or 

 sculptured and spiny, in 1 or 2 sections; chromatophores parietal, 

 varied in shape, disc-like, band-like, or lobed plates; pyrenoids and 

 reddish oil bodies and pigment-spots ( ? ) usually present; reproduc- 

 tion by aplanospores or zoospores. 



This is an artificial family erected to include the one-celled 

 Heterococcales which are free-living and which do not increase in 

 length. It no doubt will be divided when more is learned about the 

 life histories and when the significance of structural features of the 

 cell wall are better understood. The sculptured forms especially 

 may constitute a separate group. 



Key to the Genera 



1. Cells solitary, attached, sessile on submerged plants Perone 



1. Cells solitary or colonial, free-floating or intermingled with other algae 2 



2. Cell wall smooth 3 



2. Cell wall sculptured or spiny 7 



3. Cells cylindrical Monallanttis 



3. Cells globose or fusiform 4 



^Cells which increase in length usually show very clearly 2 cross breaks in the wall, one 

 near either end of the cell, with an interconnecting cylindrical and newer wall piece. See 

 Chlorothecium. 



[348] 



