16 THE PHYCOMYCETES 



vided bv septa into a number of cells. The thallus is unbranched 

 in Achlvos^eton and Myzocvtium, whereas in Las^enidium it is 

 more or less profusely branched. Each cell of the thallus eventu- 

 ally becomes transformed into a sporangium, an oogonium, or 

 an antheridium. In asexual reproduction an exit tube from the 

 sporangium penetrates the cell ^^•all of the host, and eventually 

 the laterally biciliate zoospores are formed. In Lagenidium and 

 Myzocytium a vesicle may or may not be present; in Achlyoe^e- 

 ton the zoospores are fully delimited within the sporangium but 

 encyst at its mouth. 



Sexual reproduction is unkno^^■n in Achlyogeton. In the re- 

 maininor genera, the plant body is homothallic, adjacent cells 

 functioning as antheridia and oogonia. The antheridium is 

 usually cylindrical, whereas the oogonium is spherical in shape, 

 but the o-ametanoria are not so well differentiated as in the higher 

 Oomycetes. The contents of the antheridium are dischargred 

 into the oogonium through a conjugation tube, and the oogonial 

 contents become transformed into thick-walled oospores. 

 Oospores may occasionally be formed parthenogenetically. The 

 conjucration tube is persistent, remaining attached to the wall of 

 the oospore. Germination of the oospore occurs by the forma- 

 tion either of a germ tube or of zoospores. Sexual reproduction 

 has been studied cytologically in only a single species, Myzo- 

 cythmi vermicohim, by Dangeard (1906), and further work is 

 necessary to clarify all the details. 



Probably also to be considered as belonging to this order is 

 Lagena radicicola [Vanterpool and Ledingham (1930)], a para- 

 site of cereal roots, reported from Canada. 



The taxonomic account of Sparrow (1943) is most useful as 

 a guide in classification of this order. The possession through- 

 out the order of an oomycetous type of sexual reproduction, 

 together with simpUcity in thallus structure, suggests that the 

 order is intermediate between the chytrids and the higj^her fila- 

 mentous oomycetes, such as the Saprolegniales [Scherffel (1925), 

 Cook (1936)]. 



» 



LITERATURE CITED 



Berdax, H., "Revision of the genus Ancylistes," MycoL, SO: 396-415, 1938. 

 Cook, W. R. I., "The genus Lagenidium Schenk, with special reference to 



L. Rabenhorstii Zopf and L. entophytinn Zopf, Arch. Protistenk., 86: 



58-59, 1936. 



