PHYCOMYCETES 161 



properly spraying with Bordeaux mixture. Seven sprayings in 

 New York have almost invariably enabled growers to control this 

 disease. The 5-5-50 formula may be recommended. 



Plasmopara Halstedii Farl. is widely distributed in the United 

 States, where it is found on various members of the Compositae, 

 especially sunflower and Jerusalem artichoke, Helianthns animus 

 and Helianthus tuberosus, species of Bidens, etc. 



XIV. SCLEROSPORA 



Cugini, G., and Traverso, G. B. La Sclerospora macrospora Sacc. parasita 

 della Zea Mays. Le Stazioni speriment. agrar. italiane. 35 : 46-49. 



Traverso, G. B. .Note critiche sopra la Sclerospora parassite di Graminacee. 

 Malpighia. 16: 280-290. 1902. 



There are perhaps three species of this genus. The species 

 which has been apparently most widely distributed and best 

 known is Sclerospora graminicola (Sacc.) Schroet. This species 

 occurs upon several grasses, especially Setaria spp. The leaves 

 are affected, and in severe attacks they may be considerably 

 rolled and shredded. The conidiophores are relatively evanes- 

 cent. They are irregular in form and generally nodulose, or of 

 irregular diameter, generally short, branched, and slightly colored 

 with conidia 12-20 X 10-18 /it. The oospores are at first densely 

 granular and hyaline in appearance, later they are slightly colored, 

 thick-walled, united with wall of oogonium, and angularly glo- 

 boidal, usually 40-42 /j, in diameter. Another important species, 

 Sclerospora macrospora Sacc, formerly known only on a few true 

 grasses, has more recently been found to be the cause of an im- 

 portant disease of corn in Italy. The tassel is the chief seat of 

 infection. Fairchild reports this fungus from the United States. 

 In this species conidiophores are unknown, and the oospores are 

 about 60-65 V- m diameter. 



XV. DOWNY MILDEW OF CRUCIFERS 



Peronospora parasitica (Pers.) De Bary 



Wager, Harold. On the Fertilization of Peronospora parasitica. Ann. 

 Bot. 14: 263-279. pi. 26. 1900. 



This fungus seems to be particularly abundant in England, but 

 it is also found in other parts of Europe and in the United States. 

 Practically all cultivated Cruciferae are more or less subject to it, 



