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1. Sexual reproduction by isogamous aplanogametes. Thallus unicel- 
lular or filamentous. Cells uninucleate chloroplasts single or 
several, usually large and of some definite shape, with pyrenoids 
........................................... VIII. Conjugatae 
2. Sexual reproduction not by isogamous aplanogametes. 
*Chloroplast single. 
+Without pyrenoids. Cells uninucleate, with a large parietal, 
reticulated or band like chloroplast. Thallus filamentous un- 
branched. .................................. .V. Microsporales 
++With one pyrenoid. Chloroplast single, central and substellate. 
Mostly subaerial. Thallus filamentous, sometimes parenchyma- 
tous or expanded by the fusion of the filaments in one plane. . , . 
IV. Schizogoniales 
+++ Pyrenoid one or more. Cells uninucleate, with a large parietal 
anastomosing chloroplast containing one or several pyrenoids. 
Thallus filamentous, simple or branched. Cell division character- 
ized by the intercalation of a new piece of cell wall between the 
mother cell and the distal end of the daughter cell. Sexual re- 
production by means of heterogamous gametes. Zoogonidia with 
an anterior circle of cilia. Exclusively fresh water forms. ..... 
.............................................. I. Oedogoniales 
** Chloroplasts generally one or more, parietal, with pyrenoids. Cells 
uninucleate. Sexual reproduction either isogamous or heterogam- 
ous, sometimes simple, but more often branched. .II. Chaetophorales 
***Chloroplasts numerous, parietal, each with a pyrenoid. Thallus 
filamentous, simple or branched, incompletely septate. Sexual re- 
production isogamous or heterogamous. Marine or fresh water. . . . 
IV. Cladophorales 
II. Thallus expanded, membranous, parenchymatous, attached at least when 
young. Cells uni-nucleate; chloroplasts single, parietal and with one 
pyrenoid. Sexual reproduction isogamous. Mostly marine forms 
III. Ulvales 
Order I. 
Oedogoniales. 
Only one family. 
Family I. 
Oedogoniaceae. 
One genus only has been reported from the state Oedogonium 
1. Oedogonium. 
KEY TO THE SPECIES OF OEDOGONIUM. 
A. Monoecious species. (Oogonia and antheridia born in same filament). 
1. Oogonia always destitute of median processes. 
a. Diameter vegetative cells 7-9 u. O. cryptoporum 
b. Diameter vegetative cells 12-19 u. 
* Terminal cell of filament with an apical bristle, short. . . .0. autumnale 
**Terminal cell without apical bristle O. fragile 
