274 OEDOGONIUM. 



A curious character of the genus is that all the motile 

 reproductive cells agree in having at the anterior clear 

 end a circle or crown of cilia. This is also the case in 

 another genus, Bulbochaete, which resembles Oedogonium 

 in most respects and like it grows in fresh water, but 

 which consists of branching filaments. 



The plant is attached at one end when young, and in 

 those species which grow in running water this condition 

 remains throughout life, the plant being attached to 

 stones and other objects in streams. Most of the species, 

 however, grow in quiet waters, especially in ponds and 

 ditches, either attached to water-plants, twigs, etc., or 

 floating freely on the surface in masses which somewhat 

 resemble those of Spirogyra, but are not so slippery. Like 

 various other Algae without a thick mucilage coat, Oedogo- 

 nium is often covered with Diatoms and other epiphytes. 



391. Culture of Oedogonium. If only sterile material 

 can be obtained, attempts should be made to induce it to 

 form sexual and asexual reproductive organs. 



(a) Keep plants in weak (O'l or 0'2 per cent.) Knop's 

 solution in a cold place, the water being chilled from 

 6 to by addition of ice from time to time, and then 

 bring the culture into a temperature of 15 or 16. In a 

 day or two abundant zoogonidia may be produced, as the 

 result of this treatment. 



(6) Sexual organs may be produced if plants are 

 placed in plenty of water, in bright light, at the ordinary 

 room temperature 15 to 20. 



Light does not seem, as a rule, to have any influence on 

 the production of zoogonidia, but it is necessary for the 

 formation of sexual organs. 



392. Structure of Thallus. Mount Oedogonium 

 threads in water. If it is an attached species (often 

 forming a fuzzy covering on water-plants) and has been 

 scraped carefully from the substratum, note the basal 

 colourless attachment disc consisting of finger-like 

 outgrowths of the lowest cell. 



