Classification of Green Algae. 165 
at similar positions along all the branches, giving rise 
to a concentric arrangement. Bi-fla gel late and quadri- 
flagellate swarmers of unknown function occur, also 
akinetes and palmelloid-states. 
::: 'Thallus a creeping basal branch-system, from which erect branches 
arise. 
3. Acroblaste. Reinsch, 1879. 
Thallus a richly branched basal plate with erect simple 
or compound branches. Cldoroplast large, single, no 
pyrenoid. 
Reproduction by numerous zoospores arising in swollen 
terminal zoosporangia. 
4. Leptosira. Borzi, 1883. 
Thallus a clustered, dichotomous branch-system. Cells 
barrel-shaped, with a single chloroplast and no 
pyrenoid. 
Reproduction by bi-flagellate zoospores and isoplano- 
gametes. Any thallus-cell may develop to a swollen 
zoosporangium or gametangium. 
5. Gongrosira. Kiitzing, 1845. 
Thallus flat or cushion-shaped, often incrusted, con¬ 
sisting of a clustered irregular branch-system. 
Chloroplast typically a single parietal plate, but 
often fragmented ; 1-3 pyrenoids occur. 
Reproduction by bi-flagellate zoospores, occurring 
in large numbers in usually terminal swollen 
zoosporangia. Isoplanogametes observed. 
6. Foreliella. Chodat, 1898. 
Thallus a straggling branch-system or sometimes pseudo 
parenchymatous, perforating fresh-water shells. Zoo¬ 
sporangia and swollen akinetes arise on the superficial 
erect branches. Zoospores not observed. 
***Thallus a creeping branch-system, devoid of erect branches. 
7. TricJiophilus. Weber v. Bosse, 1887. 
Thallus an irregular branch-system, all in one plane, 
and sometimes concrescent to form a disc. Cells 
thick-walled with several small chloroplasts and no 
pyrenoid. Zoosporangia intercalary, swollen, and 
containing swarmers of an uncertain nature. 
8. Gloeoplax. Schmidle, 1899. 
Thallus a flat mucilaginous matrix in which are 
embedded a number of short branch segments, any 
cell of which may swell up to form a zoosporangium. 
Zoospores bi-flagellate and germinating to re-form 
this palmelloid mucilaginous mass. 
[The affinities of this alga are obscure, and possibly the whole life- 
history is not yet known.] 
