3. Filaments with setae or hairs, not forming zoospores in special sporangia ... 4 



4. Filaments forming monostromatic expansions or cushions, 

 bearing setae which are sheathed at the base; sexual 



reproduction oogamous colecx:haetaceae (in part) 



4. Filaments forming prostrate or erect thalli, sometimes 

 both types of thalli shown by the same plant; branches 

 usually tapering ( see Microthamnion, however ) and 

 setiferous; setae and hairs not sheathed chaetophoraceae 



FAMILY CHAETOPHORACEAE 



In this family, as the name imphes, most of the genera bear setae 

 or hairs. These may develop as outgrowths of the cell wall or they 

 may be formed by the attenuation of cells toward the apices of the 

 branches, forming short or long hyaline bristles, one or more cells 

 in length. The two chief expressions of these plants are the erect, 

 branched filament, and the prostrate, cushion-like expansion. In 

 some forms the thallus involves both a horizontal and an erect por- 

 tion. In prostrate species the thallus may be a single layer of cells 

 or it may be cushion-like and several cells in depth, especially in the 

 center, becoming 1-celled in thickness at the margin. In such plants 

 the true filamentous character may be lost because of the compact- 

 ness of the cells and the irregular habit of branching. 



Key to the Genera 



1. Plant a prostrate or creeping filament, little or not at all branched 2 



1. Plant a much-branched filament; filaments 

 often adjoined and forming erect tufts, or 



pseudoparenchymatous expansions — 3 



2. Filament creeping, little or not at all 



branched, if so, with branches not erect Aphanochaete 



2. Filaments creeping,. with infrequent, short branches Chaetonema 



3. Plant consisting of an axial row of large, barrel-shaped or cylindrical 

 cells giving rise to nodal whorls of branches, or oppositely arranged 

 fascicles, of much smaller cells; thallus inclosed 



in a soft, copious mucilage Draparnaldia 



3. Plants without an axial row of distinctly larger cells; branch cells 



about the same size as those of the main axis 4 



4. Plant a branched filament, the cells of the branches scarcely smaller 

 than those of the main axis, gradually tapering to long or short setae 

 or to pointed apical cells; horizontal or prostrate portion of the 

 thallus often present; thallus inclosed in a thin mucilage which 



may not be evident — Stigeoclonium 



4. Plant not as above 5 



5. Plant an erect, branched filament 6 



5. Plant a horizontal or pseudoparenchymatous expansion — - 7 



6. Plant a much-branched filament inclosed in firm, copious mucilage, 

 forming macroscopic thalli of definite 



shape; branches attenuate Chaetophora 



6. Plant microscopic; branches not at all or scarcely 



attenuate; investing mucilage wanting Microthamnion 



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