98 THE PHYCOMYCETES 



"A studv of the water molds and Pythiums occurring in the soils of 



Chapei Hill," /. Elisha Mitchell ScL Soc, 41: 151-164, 1935. 

 HoHNK, A\\, ''Saprolegniales und Alonoblepharidales aus der Umgebung 



Bremens, mit besonderer Berucksichtigung der Oekologie der Sapro- 



legniaceae," Abkandl. Nat. Ver. Brd7?ien, ^29: 207-2}7, 1935. 

 "Zur Cytologic der Oogon- und Eientwickelung bei Saprolegnia ferax,''^ 



Abbaiidl. Nat. Ver. Bremen, 25^:308-323, 1935a. 

 Kasaxowsky, v., ''''Aphanomyces laevis de Bary. I. Entwickelung der 



Sexualorgane und Befruchtung," Ber. dent, botan. Ges., 25^:210-228, 



1911. 

 Kexdrick, James B., "The black-root disease of radish," Indiana Agr. Expt. 



Sta. Bull., 311. 32 pp. 1927. 

 PArrERSON, P. AL, "Fertilization and oogenesis in Acblya colorata,'" J. Elisha 



Mitchell Sci. Soc, 43: 108-123, 1927. 

 Raper, J. R., "Heterothallism and sterility in Achlva and obser^-ations on 



the cvtologv of Achlya bisexnalis,^'' J. Elisha Mitchell Sci. Soc, 52: 



274^289, 19V6. 

 "Sexuaht}^ in Achlya ainbisexualis,'" My col., 32: 710-727, 1940. 

 ScHR-\DER, E., "Die Entwickelung von Thraiistotheca clavata,''^ Flora, N. P., 



32: 125-150, 1938. 

 Shaxor, Lelaxd, "Observations on the development and cvtologv of the 



sexual organs of Thraiistotheca clavata (de Bary) Humph.," /. Elisha 



Mitchell ^Sci. Soc, 53: 119-135, 1937. 

 Tiffxey, W. X., "The host range of Saprolegnia parasitica,^'' My col., 31: 



310-321, 1939. 

 "The identity of certain species of the Saprolegniaceae parasitic to fish," 



/. Elisha Mitchell Sci. Soc, 55: 134-151, 1939a. 

 Wolf, F. T., "Cytological observations on gametogenesis and fertiliza- 

 tion in Achlya flagellata,'" My col., 30: 456-467, 1938. 



PYTHIALES 



The Pvthiales are characterized by possession of a well-devel- 

 oped mycelium that lacks haustoria and that bears sporangia 

 sympodially and in succession at the tips of sporangiophores 

 which are little differentiated from the mycelium. It is a small 

 group, intermediate phylogenetically between the Leptomitales 

 and Peronosporales. A wide diversity of opinion exists among 

 mycologists on generic and specific limits ^^'ithin the order. 

 Some workers maintain that there are only 4 or 5 o-enera; others 

 recognize as many as 14. Of these Pvthium and Phytophthora, 

 which some students would combine, are the best known, are of 

 most importance, and contain the larger number of species. 

 These two genera include destructive pathogens capable of at- 

 tacking both herbaceous and woody plants and also of main- 



