38 SPECIES OF ALGJE. 



b. Marine; 1-4 mm. long in close fringe; branches rarely opposite, 



often hairy virgatula, 61 



c. Terminal cells cuspidate or piliferous .... Hermannii, 60 

 c. " " rounded pygnuza, 61 



7. HILDEBRANTIA. 



a. Fresh water; cells red; on river stones rivularis, 61 



a. Marine; cells spherical rosea, 62 



8. COMPSOPOGON. 



One species cceruleus, 62 



9. COLEOCH^ETE. 



A. Filaments irregularly disposed, variable in form . irregularts, 65 



A. radiating (a). 



a. Filaments not laterally adhering, forming small disks . soluta^ 64 



a. " adhering side to side, forming a disk (b). 



b. Disk irregularly orbicular; cells subquadrangular . . scutata, ^4 



b, " exactly orbicular, thin, flat, orbicularis, 64 



b. " orbicular, upper surface rounded, about 2 mm. high, 



pulvinata, 64 



10. CEDOGONIUM. 



It is only possible to identify the sixty-three species of this genus 

 when the plants are in fruit, the forms being arranged in groups ac- 

 cording to some characteristic or peculiarity of the oospore (the seed 

 or spore), and of the oogonium (the sac containing the oospore). It 

 is therefore scarcely possible to devise an artificial key. 



Male and female organs on the same plant (A). 

 Male and female organs on different plants (B). 

 Male organs of fructification not known (C), 

 A. Oospores globose or nearly so (D). 



A. " elliptical or ovate (/). 



B. Males short (dwarf), i -celled (k). 



B. Males short (dwarf), 2 many-celled (/). 



B. Males filamentous, many-celled plants (gg). 



C. Oospores globose or nearly so (//). 



C. " elliptical or ovoid (ss). 



D. Oogonia globose or nearly so (a). 

 D. " elliptical or ovoid (h). 



a. Oogonia opening by a pore (b). 



a. " " lid (/). 



b. Pore median; veg. cells 4-6 times as long as wide . cryptoporum, 70 



