margins, 24-28/a in diameter, 37-44/* long. Male filaments 11-14/* in 

 diameter, 20-31/* long. 



Mich. 



OEDOGONIUM Link 1820, p. 5 



Attached, unbranched filaments (sometimes becoming free-floating 

 in age ) . Cells cylindrical or enlarged toward the anterior end, where 

 one or more ring-like scars resulting from cell division are usually 

 apparent. Chloroplast a parietal reticulum with many pyrenoids. 

 Nucleus at the periphery of the protoplast. Swollen female cells 

 (oogonia) present at maturity, one to several in each filament. 

 Male cells (antheridia) either short, compartment-like cells, each 

 bearing one or two antherozoids, occurring in filaments the same 

 size as those which bear the oogonia, or minute male filaments 

 growing epiphytically on the female plants. Fertilization by the 

 entrance of an antherozoid through a pore or lid of the oogonium 

 wall; resulting oospore of various shapes, surrounded by a wall of 

 two or three layers, which may be smooth or variously decorated. 



In the identification of Oedogonium species, the size of the 

 vegetative cells, the shape and size of the oogonia, the form and 

 decoration of the oospore wall, and the location of the antheridial 

 cells are the more important differentiating and specific characters. 

 There is no single specific feature which may be used for identifica- 

 tion purposes but rather a combination of the above-mentioned 

 features. Some of these (such as size, for example) vary considerably 

 within a given species, and the student should bear this in mind, 

 especially when using keys. Less than half the known species of 

 Oedogonium are listed here; consequently the key is incomplete. 

 The reader is referred to Tiffany (1930, 1937) when plants in 

 question cannot be identified by the scheme used below. 



The genus Oedogonium is a large one and is easily divided into 

 10 sections on the basis of the location of the male sex organs and 

 the character of the oogonium. Following are keys, one to the 

 sections and one to the species. (The species are alphabetically 

 arranged within each section. ) 



Key to the Sections of the Genus Oedogonium 



1. Plants dioecious, the male plants dwarfed and epiphytic 



on the female ( nannandrous ) 2 



1. Plants dioecious or monoecious, the male plants approximately the same 

 size as the female plants, or with the antheridia in 



the same filament as the oogonia 7 



2. Plants idioandrosporous , 3 



2. Plants gynandrosporous, or both gynandrosporous and 



idioandrosporous in the same species 4 



f 156] 



