I'EliONOSPOUALES 193 



may be recognized. Since the oospores of this genus were first 

 described by de Bary (1863) under the name Cydopus she 

 attributes the genus to him rather than to Leveille who first 

 used the name Cystopus for the sporangial stage alone. 



The wording of the rule is such as to leave open to question 

 the necessity of its application to the Phycomycetes, and in 

 other respects its meaning is not clear. Some workers (e.g., 

 Murphy 1918) have interpreted it as excluding the Phycomycetes. 

 Until it is further elucidated the writer prefers to retain the 

 name Albugo, now well established in the American literature. 



Pythiaceae 



The members of this family are clearly the most primitive 

 of the Peronosporales, and in certain respects stand as an inter- 

 mediate group between the Saprolegniaceae and Leptomitaceae 

 on the one hand, and the Peronosporaceae on the other. In the 

 lower members of the group the habit is aquatic, the sporangia 

 remain attached, and swarmspores constitute the usual method 

 of asexual propogation. In the higher members the habit is 

 terrestrial, the sporangia are deciduous, and germination is 

 sometimes by germ tube. Intermediate species exemplify inter- 

 mediate conditions. Parasitism is less highly developed through- 

 out the group than in the Peronosporaceae, and apparently is 

 never obligate. In some of the most highly developed forms 

 (e.g., Phytophthora infestans) a definite sporangiophore is devel- 

 oped, but in most cases the hyphae which bear the sporangia 

 are not sharply differentiated from those of the vegetative 

 mycelium. Even when a specialized sporangiophore is pres- 

 ent it does not mature its sporangia simultaneously at the 

 tips of its branches as in the Peronosporaceae. Instead, they are 

 developed successively, sporangia of different ages existing 

 together on the same sporangiophore. Moreover, the spo- 

 rangiophore m.ay develop extensively even after some of the 

 sporangia have reached maturity. The mycelium in the Pythia- 

 ceae is of small diameter (S-A/jl, rarely 7ai), is abundantly and 

 irregularly branched in most species, and may be septate at 

 maturity. (See Jour. Agric. Res, 40: 557, for "diplanetism.") 



The family was placed by Schroter (1893) in the Saproleg- 

 niales, but most authors have included it in the Peronosporales. 

 Its intermediate character has rendered difficult the task of 

 finding a satisfactory basis for a taxonomic separation of the 



