i 64 Blackman and Tansley. 
The spherical oospore rests for a long time, still retaining its 
chloroplast and then germinates by dividing into a radiating cluster of 
about thirty cells. In each of these resulting thin-walled cells there 
develops a single bi-fhigellate zoospore which escapes by rupture of 
the cell-wall. The zoospores after swarming grow at once into new 
plants. 
Genus. 
Colcocluiete. Brebisson, 1844 . 
Thallus a tuft of straggling branches, or a cushion of 
concrescent branches, or a flat monostromatic plate. 
The zoospores and the antherozoids arise singly in any 
of the cells of the thallus or only in the end cells of 
branches; eye-spot absent. 
[This family is separated from the three previous families by the 
occurrence of oogamy and the indirect germination of the oospore. 
The range of forms of thallus-reduction is very wide for a single genus 
but they are strictly comparable with different types of the Chaeto- 
phoraceae. The presence of sheathed setae suggests a common origin 
for this family and the previous one and the germination of the zoosporesof 
some species oiColcochactc recalls the mode of g\o\v\A\o[CliactosphaeriiUum~\ 
Fam. IX. Chroolepidaceae. 
Thallus hydrophytic or aerial , consisting of a more or less 
concrescent branch-system, without hairs , setae } or filar processes , and 
usually attached by a wide base. 
Chloroplast a single parietal plate, usually devoid of pyrenoid. 
Reproduction bv zoospores (typically bi-flagellate), arising in 
large numbers in a zoosporangium which usually dippers distinctly in 
size or shape from the vegetative cells. Isoplanogametes have also 
been observed in some cases. 
[This family stands opposed to the four previous families collectively 
by having no tendency to form hairs, setae, or filar processes, but like 
those families, it is apparently made up of reduction-series of forms 
derived from fretly branched types, 't hese hairless series have probably 
a common origin with the Chaetophoraceae; the lower members, 
however, are at present imperfectly known.] 
Sub-Family I. 
Gongrosireae. Hydrophytic forms devoid of haematochrom. 
Genera. 
*Thallus erect, freely branched with a small basal attachment. 
1 . Microth amnion. Nageli, 1849 . 
Thallus a di- or trichotomous branch-system, epiphytic 
by a basal cell. Branches elongated and quite free 
from one another. Cells cylindrical, long, with a 
single parietal chloroplast and no pyrenoid. Zoospo- 
rangia arise by swelling of the terminal cells of the 
branches, but the free zoospores have not been 
observed. Gametes unknown. 
2 . Chlorotylium. Kutzing, 1843 . 
Thallus a hemispherical cluster of branches, imbedded 
in mucilage and often calcified. Swollen cells occur 
