Classification of Green Algce. 135 
1-5 nuclei. Sporangia arise by the swelling of single 
thallus-“cells ” and attain a very large size, usually 
developing adventitious rhizoids. The contents may 
divide to form (a) many bi-flagellate zoospores which 
germinate into a new thallus, or (b) a few large 
aplanospores which germinate in situ or after escaping 
[The unique sporangia and the specialisation due to the peculiar 
habitat leave the exact affinities of this genus obscure.] 
Fam. IX. Cladophorace^e. 
Thallus filamentous, branched or unbranched, abundantly septate 
with two or more , often many, nuclei to each segment. 
Chromatophore a perforated parietal plate or a network of 
polygonal discs. Pyrenoids many. Reproduction by bi-or-quadri- 
flagellate zoospores , akinetes or bi-flagellate isoplanogamctes. All the 
genera except Pithophora are marine. 
[By Schmitz and other algologists this family is held to be derived 
from the filamentous branched Valoniaceae, and the strong similarity of 
the cytological characters of Cladophora with those of Microdictyun , 
Siphonocladus, etc., certainly supports this view. If Cladophora is the 
primitive form, the simple almost unbranched genera with but few nuclei 
in each segmeut must be regarded as reduced forms. 
Usually, however, the unbranched forms in any mixed family are the 
primitive ones, and it is possible that in this case they have been derived 
from an unbranched filament of the Ulotrichoid type by increasing 
suppression of the formation of septa between dividing nuclei. Wille’s 
account of the simplest species of Rhizoclonium strongly supports this 
view. Further cytological investigations may decide between these 
theories, but at present systematists are agreed that it is hardly possible 
rigidly to separate Cladophora from Rhizoclonium .] 
Genera. 
1. Urospora. Areschoug, 1866. 
Filament usually unbranched, the attachment strength¬ 
ened by endo-mucilaginous rhizoids. Nuclei several. 
Zoospore quadri-flagellate. 
2. Chaetomorpha. Kiitzing, 1845. 
Filament unbranched, attached when young by a long 
“cell” with branched unseptate free rhizoids. Segments 
broad. Nuclei several. Zoospores bi-flagellate. 
3. Rhizoclonium. Kiitzing, 1843. 
Filament creeping, usually unbranched, but bearing free 
rhizoid-outgrowths from some of the “cells” ; attached 
when young by a basal cell. Segments narrow. 
Nuclei 2—4, occasionally one. 
4. Cladophora. Kiitzing, 1843. 
Filaments more or less branched, free or in clumps, the 
attachment strengthened by endo-mucilaginous rhi¬ 
zoids. “Cells” large with very many nuclei and a net¬ 
work of discoid chloroplasts. Zoospores quadri- 
flagellate. Isogametes bi-flagellate. 
