Classification of Green Algce. 139 
Cliloroplast a single parietal plate of irregular form, which may be 
locally thinned or perforated, and in a few cases may he broken up 
into a number of separate discs. Pyrenoids present. 
Reproduction typically by quadri-jlagellate zoospores arising in 
zoosporangia, which closely resemble the vegetative cells, and also by 
bi-flagellate isoplanogametes. The occurrence of mega- and micro- 
planogametes has, however, been proved for one genus. Akinetes 
and palmelloid stages are usual. 
[This family contains a large number of genera often not sharply 
separable, which seem to form a series in which the branch-system 
became more and more reduced from the Stigeuclonium type—with a 
small attachment-plate and abundant erect branches—to forms which 
consist only of a small plate without any free branches. The branches 
become reduced, successively, in this series to (1) true “hairs” (a 
sequence of one or more tapering elongated cells with nuclei, and poor 
in chlorophyll) then to (2) “setae” (long tapering extensions of cells 
with a definite lumen and containing protoplasm but no nucleus or 
chlorophyll, and only secondarily shut off from the cavity of the 
generating cell by local swelling of the walls) and finally to (3) “filar 
processes” (which are very fine tapering outgrowths of the cell-wall 
only, mucilaginous in nature, and entirely devoid of lumen or contents). 
The abundance of these reduced structures is known to be determined by 
external conditions and some species and genera in their natural 
habitats have very few or none.] 
Genera. 
: Thallus with abundant erect tapering branches and attached by a 
small basal plate of coherent branches to a substratum; rarely 
epiphytic. End-cells of branches always tapering and 
poor in chlorophyll. 
1. Stigeoclonium. Kiitzing, 1843. 
Thallus form very variable, devoid of a main axis, 
branching of erect part is lateral and irregular; branches 
all quite free and without mucilaginous investment. 
Chloroplast a parietal band lining all or part of the 
cell-wall. Reproduction by quadri-flagellate zoospores 
and bi-flagellate isogametes. 
2. Chaetophora. Schrank, 1789. 
Thallus an erect branch system, without a main axis? 
imbedded in dense mucilage which may be cushion¬ 
shaped or foliaceous and lobed. All branches end in 
very long tapering colourless cells. 
Reproduction by bi-flagellate zoospores alone observed. 
3. Draparnaldia. Bory, 1808. 
Thallus a straggling erect branch system with an 
obvious main axis on which tufts of small lateral 
branches with tapering ends are borne regularly. 
The cells of the main axis are very large and the 
chloroplast only occupies their central zone. 
Reproduction by quadri-flagellate zoospores alone 
observed. 
