Chapter IV 

 EUPHYCOPHYTA 



CHLOROPHYCEAE {continued) 



oedogoniales3 chaetophorales5 

 siphonocladales5 dasycladales 



* Oedogoniales 



Three genera, Oedogonium, Oedocladium and Bulhochaete are com- 

 prised in this order. They are characterized by the presence of 

 motile bodies with a ring of cilia around their anterior end. Because 

 of this they were placed in earher classifications in a special group 

 called the Stephanokontae. The mode of ordinary cell division is 

 also unique (see below). Sexual reproduction is by means of an ad- 

 vanced type of oogamy (see below) not found in any other order. 

 These characters indicate that the order represents a speciaUzed 

 end Hne in the evolution of the green algae. The species are all 

 fresh water and their taxonomy is difficult because it depends on a 

 knowledge of the sexual plants and type of reproduction. 



* Oedogonium {oedo, sv/dling ; gonium, vessel). Figs. 35, 36 



The three genera, Oedogonium, Oedocladium and Bulhochaete, 

 which comprise this order were at one time classed as a separate 

 group, the Stephanokontae. Under the new scheme of classifica- 

 tion, however, they must be regarded, together with the other 

 members of the old Isokontae, as forming the Chlorophyceae. 



In Oedogonium the thallus consists of long unbranched threads 

 which are attached when young, though later they become free- 

 floating, whilst in the other two genera the filaments are commonly 

 branched. Each cell possesses a single nucleus together with an 

 elaborate reticulate chloroplast containing numerous pyrenoids. 

 The cell wall contains, according to some workers, an outer layer of 

 a chitinous material, and if they are correct this is of great interest 

 because chitin is essentially an animal substance. The chromo- 

 somes of Oedogonium are especially interesting among those of the 



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