LEPTOMITALES 871 



ings by Gilpin (1954) on the carbon and nitrogen requirements for 

 growth in Apodachlya brachynema do not completely agree with prev- 

 ious reports on nutrition in this species. Those interested should consult 

 his paper. With respect to the Rhipidiaceae, Minden (1916) earlier 

 described the growing in culture of species of Rhipidium and Araiospora 

 in various natural and synthetic media. Subsequently, Bishop (1940) 

 pointed out something of the nutritional requirements of Sapromyces 

 elongatus ("S. reinschii"), but neither of these workers attempted a 

 comprehensive study nor presented an extensive analysis of his results. 

 Emerson (1950) isolated Rhipidium americanum in pure artificial culture 

 by streaking zoospores, produced at 15°C, on agar plates of glucose- 

 yeast media. Similarly, he also brought Sapromyces androgynus into 

 pure culture and, very recently (comm.), Mindeniella spinospora. 

 Webster (1943) mentioned that Araiospora streptandra had been brought 

 into pure culture and that the formation of spiny sporangia was aided 

 by favorable conditions of nutrition, smooth ones by reduction of 

 nutrition. He also said that smooth-walled sporangia discharge their 

 zoospores "in a shorter time" than do the spiny ones, and that they are 

 the chief means of dispersal of the species. 



SYSTEMATIC ACCOUNT 



LEPTOMITALES 



Microscopic saprophytic fresh-water fungi, the thallus with or without 

 a well-defined basal cell and holdfasts, the hyphae divided into constrict- 

 ed pseudocells by pseudosepta of cellulin, walls giving a cellulose reac- 

 tion; reproductive organs consisting of segments of the hyphae or 

 specialized pedicellate structures cut off by cross walls and constrictions 

 from the attendant mycelium; zoosporangia forming mono- or dipla- 

 netic biflagellate zoospores ; oogonia with or without periplasm, forming 

 (except in Apodachlyella) a single egg; antheridium either a single seg- 

 ment or borne on specialized branches of mono- or diclinous origin, 

 with or without a fertilization tube; oospores single (except in Apo- 

 dachlyella), thick-walled, upon germination forming hyphae. 



The order differs from the Saprolegniales primarily in the division of 



