t 38 
Blackman and Tansley. 
4. Binuclearici Wittrock, 1886. 
Thallus with no distinction between apex and base. 
Older transverse cell walls considerably thickened, 
Chromatophore ring-shaped with no pyrenoid and 
producing oil. Reproduction by akinetes, which 
germinate in situ. Motile cells unknown. 
[It is very doubtful if this genus is correctly placed here.] 
Fam. II. Pkasiolace^e. 
Thallus a simple unbranched thread or band-shaped to leaf-like 
by longitudinal division of the cells, any of which may produce a 
rhizoid. Chromatophore central, star-shaped , with a single central 
pyrenoid. 
Reproduction by the formation of akinetes and aplanospores. 
Motile cells unknown. 
Prasiola. C. A. Agardh 1821. 
Characters of the family. 
[This genus, in which Schisuguniuw, Kutzing, is included, is often 
placed in Ulvaceae, but it seems much more probable that it has 
descended from a filamentous form.] 
Fam. III. Microspo raceme. 
Thallus an unbranched, free-floating filament. 
In the growth of the cell-wall the freshly formed layers are 
not continuous along the length of the cell, hut are so laid down that 
the filament separates into “ H-pieces f each corresponding with the 
halves of two adjacent cells, at the escape of the zoospores. Chromato- 
phores several in a cell, band-shaped , constricted at intervals. 
Pyrenoids absent. Zoospores 4-flagellate. Gametes (?) biflagellate. 
Microspora. Lagerheim, 1888. 
Characters of the family. 
[This genus has been placed in a separate family on account of its 
peculiar characters. Its immediate affinities are not clear.] 
Fam. IV. Cylindrocapsace^:. 
Thallus of an unbranched filament, attached when young. Cell-walls 
thick, often shewing layering. Chromatophore parietal with a single 
pyrenoid. 
Reproduction by biflagellate zoospores of two sizes, by akinetes, 
and by antherozoids and eggs, which are developed from ordinary 
vegetative cells. 
Cylindrocapsa. Reinsch, 1867. 
Characters of the family. 
[The immediate affinities of this genus are obscure.] 
Fam. V. Chartophorace^:, 
Thallus always attached, usually epiphytic or endophytic, composed 
of an attachment-plate oj concrescent branched cells and of erect branches 
more or less developed, which usually bear or are replaced by * hairs,' 
‘ setae' or *filar processes.’ Cells elongated, or polygonal by compression. 
