LAGENIDIALES 



IS 



With the removal of the type genus there is left a more uni- 

 fied group of 3 genera, Lagenidium, Myzocytium, and Achlyoge- 

 ton, all of which were originally described by Schenk (1857, 

 1858, 1859). Lagenidium is the largest genus, having about 15 

 species [Cook (1936)]; Achlyogeton is monotypic. The group 



Fig. 21. A. Portion of thallus of Lagenidiimt rabeiiborstii, showing swarm 



spores in vesicle, an empty sporangium, and two cells, an antheridium and 



oogonium. B. Lagenidhnn mnericaninn. (After Atkinson.) 



has been monographed by Schroter (1893) and von Minden 

 (1915), and the Japanese forms have recently been studied by 

 Tokunaga (1934). The species for the most part are obligate 

 parasites of desmids, diatoms, and filamentous green algae. A 

 single representative, hageiiidhnn giganteinn, has been grown in 

 pure culture [Couch (1935)]. 



The thallus throughout the order is not extensive, being usually 

 confined to a single host cell. A young thallus generally takes 

 the form of a unicellular cylindrical tube, which later becomes di- 



