PERONOSPO RALES 1051 



in groups of four, at the tips of short verticellate supporting hyphae, 

 30-35 [L, germinating by zoospores or a hypha; zoospores laterally 

 biflagellate, swarming briefly before encystment; oogonium spherical, 

 25 [x in diameter; oospore nearly completely filling the oogonium, with 

 a large central oil globule. 



Saprophytic in soil, capable experimentally of causing root rot of 

 various phanerogams, United States ; Germany. 



Evaluation of Diasporangium jonesianum is unfortunately hampered 

 by the fragmentary evidence on zoospore development and discharge. 

 Although separation of the protoplasm outside the sporangium into 

 masses, as in Pyt/uogeton, was noted, Hohnk considered it abnormal. 

 In the few cases of zoospore formation that he saw, the process was 

 completed within the sporangium and the zoospores emerged fully form- 

 ed as in Phytophthora. Only scant observations on the sex organs were 

 recorded, but a true peronosporaceous oospore is figured. 



The most impressive distinguishing character, it seems to this writer, 

 is the Pythiogeton-Wkt, verticellate sporangia, which typically produce 

 the zoospores endogenously and without a vesicle. New investigations 

 will undoubtedly establish the genus on a firmer basis and make clear 

 generic versus specific differences. 



PHYTOPHTHORA de Bary h 2 



J. Roy. Agr. Soc. England (2d ser., 1),12: 240, figs. 1-8. 1876 



(Figs. 89 A-G, p. 1055; 90. p. 1059) 



Kawakamia Miyabe, Bot. Mag. Tokyo, 17: 306. 1903. 

 Myeelopfiagus Mangin, C. R. Acad. Sci. Paris, 136: 472. 1903. 

 Phloeophthora Klebahn, Centralbl. Bakt. Abt. II, 15: 336. 1906. 

 Pythiacystis R. E. Smith and E. H. Smith, Bot. Gaz., 42: 221. 1906. 

 Pythiomorpha H. E. Petersen, Bot. Tidsskrift, 29: 391. 1909. 

 Nozemia Pethybridge, Sci. Proc. Royal Dublin Soc. (N. S.), 13: 556. 1913. 

 Blepharospora Petri, R. C. Accad., Lincei , V, 26: 299. 1917. 

 Pseudopythium Sideris, nom. mid., Phytopath., 20: 953. 1930. 



1 The writer feels strongly his own inadequacy in formulating this generic de- 

 scription. It was made necessary by the total lack of a formal diagnosis (in English) 

 of the genus in Tucker's (1931) monograph. A parallel remark applies to the generic 

 description given for Pythium (p. 1031 ). 



2 See also Waterhouse's (1956) recent account. 



