PERONOSPORALES 33 



P. pygmaea on various Ranunculaceae, P. Halstedii on various 

 Compositae, P. australis on Cucurbitaceae, P. obdticens on the 

 cotyledons of seedling Inipatiens, and several other species on 

 various hosts. Of the forms which germinate without zoospores, 

 Bremia has a single species parasitic on lettuce and allied 

 plants, while Peronospora has numerous species parasitic on a 

 wide range of host plants. 



LITERATURE. 



Fischer. Loc. cit. 383-489. 



Schroeter. Loc. cit. 108-119. 



Saccardo. Sylloge Fungorum, 7: 233-264; 9: 340-345; n: 

 242-244. 



The following include more or less complete enumerations, 

 descriptions and notes on American species : 



Farlow. Enumeration of the Peronosporeae of the United 

 States. Bot. Gaz. 8 : 305-315 ; 327-337. 1883. 



Farlow. Additions to the Peronosporeae of the United States. 

 Bot. Gaz. 9 : 37-40. 1884. 



Swingle. Some Peronosporaceae in the Herbarium of the Divi- 

 sion of Vegetable Pathology. Jour. Mycol. 7 : 109-130. 1892. 



The Phycomycetes may properly be regarded as the descend- 

 ants of degenerate algae which have lost their power of inde- 

 pendent existence through parasitism. They have probably 

 descended not from any single ancestral algal stock, but different 

 members have risen from various parent stocks. 



