210 AGRICULTURAL EXPERLMENT STATION. [Jan. 



made during the past season, and it is hoped that the work 

 of the coming year may shed some hghton these questions, 

 which bear so directly and so practically on the treatment 

 and prevention of the disease. 



The Cucumber Mildew. — Plasnioj^ara Cubensis 

 (B. & C). 



In 1868, Berkeley and Curtis described* a fungus of the 

 Dovjuy Mildezu group from specimens on a cucurbitaceous 

 plant from Cuba, under the name Pcronospo?'a Cubensis. 

 This fungus remained then comparatively unknown for 

 twenty years ; but meanwhile Spegazzini f had described a 

 species on a cucurbitaceous host from the Argentine Re- 

 public, which he called Pcronospora aiistralis, and Trel- 

 ease:]: found the same species on the one-seeded star 

 cucumber {Sicyos augiilatiis), in Wisconsin. 



In 1889 Dr. W. G. Farlow § reported having .received 

 from Japan the previous year a fungus on cucumber leaves, 

 and in 1889, from New Jersey, the same fungus on the 

 leaves of hot-bed cucumbers. The same fungus appeared 

 during 1889 on leaves of cucumbers and squashes in vari- 

 ous parts of the country, and seemed likely to become a 

 serious pest. The structure of the fungus is quite different 

 from that of the only mildew heretofore known on Cncurbi- 

 tacccB in the United States, namely, Peronospora austral is 

 (compare Figs. 11 and 15) ; but a comparison with orig- 

 inal specimens of the little-known P. Cubensis has shown it 

 to be undoubtedly that species. Its almost simultaneous 

 discovery in widely separated parts of the earth, where it 

 had previously been wholly unknown, is a remarkable 

 instance of the apparent vagaries of fungous epidemics, 

 and shows how much we have yet to learn of the condi- 

 tions which govern them. 



This fungus attacked with fatal result a plot of cucum- 

 bers in Amherst the past season, and was received on 



* Journal LinnsEan Society, Botany, Vol. X, p. 363. 



t Annales Sociedad Cientif. Argentina, 1881, XII, p. 81. 



X Botanical Gazette, 1883, p. 331 ; see also Paras. Fungi Wisconsin, p. 6. 



§ Botanical Gazette, 1889, p. 187. 



