THE GREEN ALGAE OF NORTH AMERICA 223 



of simple or branching filaments, of a single series of uninucle- 

 ate cells ; chromatophores generally of many longitudinal bands, 

 with many pyrenoids ; cell division by the rupture of a circular 

 ring, which forms the membrane of the new cell. Asexual re- 

 production by multiciliate zoospores, each produced from the 

 entire contents of a cell, and germinating immediately ; also in 

 some cases by akinetes. Sexual reproduction by oogonia and 

 antheridia ; oogonia single or seriate, formed by transformation 

 of vegetative cells ; opening by a lid or a pore to admit the 

 spermatozoids ; when fertilized the oospore assumes a mem- 

 brane ; after a period of rest the oospore produces four zoospores 

 (occasionally fewer or more), which germinate at once. Anther- 

 idia either in the same filament with the oogonia or in separate 

 individuals ; male plants either of about the same sized cells as 

 the female plants, or much smaller ; in the latter case the male 

 plants arise from androspores, similar to zoospores but smaller ; 

 spermatozoids produced one or two in an antheridium, smaller 

 than the androspores, but of similar appearance. Fresh water. 



The Oedogoniaceae are distinct from all other families, only 

 the very small family of the Cylindrocapsaceae showing any 

 near relationship. There are two genera of world- wide dis- 

 tribution, Oedogonium and Bulbochaete ; Oedocladium, a mono- 

 typic genus, is found in Europe. 



The vegetative structure is of the simplest, but the mode of 

 cell division is found nowhere else ; the reproductive characters 

 are elaborate and varied, and the special variations peculiar to 

 the different species seem to be quite constant. A very thor- 

 ough study of the family has been made by Hirn, and his mono- 

 graph is the basis for the following pages ; his descriptions have 

 been closely followed, few changes or additions being required 

 for present purposes. 



i. OEDOGONIUM Link, 1820, p. 5. 



Frond of a single, unbranched series of cells, vegetative cells 

 cylindrical, rarely with constrictions; basal cell with holdfast ; 

 terminal cell obtuse, apiculate or produced into a lon^ seta ; all 

 cells capable of division ; oogonia produced dirt-ctly by division 

 of a vegetative cell. 



In this genus there are more definite characters for distinc- 

 tion of species than in any other of the larger genera of grei ' 

 algae, and these characters are qu'te constant in each specie> ; 

 abnormal developments are of course to be expected, but tiny 



