PERONOSPORALES 203 



which later the oospore develops. The mature sexual apparatus 

 thus consists of a balloon-shaped oogonium with a thick-walled 

 oospore in its upper swollen portion and with its funnel-shaped 

 base within and surrounded by the antheridium. Murphy 

 studied cytologically a member of this group, Phy. erythroseptica, 

 and demonstrated that, following the protrusion of a receptive 

 papilla (manocyst) into the antheridium, a fertilization tube 

 enters the oogonium and discharges into it a single male nucleus 

 which later fuses with a nucleus in the oosphere. In other 

 species of the genus, designated the cadorum group, sexual 

 organs of the usual oomycetous type are developed, the antherid- 

 ium being applied more or less laterally and sending into the 

 oogonium a fertilization tube as in Pythium. Pethybridge, 

 impressed by the unique type of sexuality in the infestans group, 

 split the genus PJujtophthora into two and applied the generic 

 name Nozemia to the members of the cadorum group, retain- 

 ing Phytophthora for the infestans group because he regarded 

 Phy. infestans as the type species of the genus. Wilson went 

 even farther and suggested the recognition of a new family 

 Phytophthoraceae and a new order Phytophthorales for the infes- 

 tans group. Since the sporangial stage is wholly similar in the two 

 groups, and since this vagary of the sexual process constitutes 

 the only difference between them, the spHtting of the genus was 

 questionable and proved to be premature. Later Lafferty and 

 Pethybridge found that in some species both basal (amphigynous) 

 and lateral (paragynous) antheridia are produced. The separa- 

 tion of tJie groups, therefore, can no longer be justified and 

 Nozemia has been abandoned. Species in which the basal type 

 of antheridium is known include Phy. infestans, Phy. phaseoli, 

 Phy. erythroseptica, Phy. parasitica, Phy. arecae, Phy. cryptogea 

 and others Only the lateral type has been observed in certain 

 others. 



Although the observations of Pethybridge concerning the 

 penetration of the antheridium by the oogonium were at first 

 received with scepticism, the observations of other workers and 

 in particular the cytological study by Murphy (1918) have cor- 

 roborated his statements. Moreover, Tabor and Bunting (1923) 

 have described and figured the same phenomenon in a new genus, 

 Trachysphaera Recently Rose and Lindegren (1925) have 

 figured for Phy. cactoruni oogonia bearing both amphigynous 

 and paragynous antheridia; and one oogonium bearing two 



