Botanical Divisioy. 809 



seems to be generally distinct as shown by the characters of 

 germination, the growth in the agar plate, and the characters of 

 fructification on a more solid artificial substratum like sterilized bean 

 stems. A full comparison it does, not now seem best to make, reserv- 

 ing it for the study of the Glop,osjjoriuras which are now in progress. 

 Figures 1 and 2 drawn with aid of camera lucida; scale = 1 mm.; 

 object magnified 30 times more than scale, 



GEO. F. ATKINSON. 



POWDERY MILDEW OF CRUCIFERS. 



A powdery mildew of certain cultivated cruciferous plants is probably 

 of common occurrence in America, but thus far it does not seem to have 

 attracted much attention. This may be because it is not very injuri- 

 ous. At present this mildew is known only in the conidial stage, on 

 crucifers, and I do not remember ever seeing any reference to its occur- 

 rence on these plants in the United States. It frequently becomes very 

 injurious to turnips in England where it has been known for some time. 

 W, G. Smith records it in his little book: "Diseases of Field and 

 Garden Crops " under the name of Oidium hahamii, Mont. 



Oidium is a form genus which includes several species that are known 

 to be the conidial stages of some pyrenomycetous fungus especially of 

 the group Erysiphece. According to Saccardo several of the micro- 

 sporous species are probably more properly referable to the genera 

 Ovularia and Ramularia* Several of the larger species of Oidium 

 have already been correllated with their ascobporous form. 



Oidium baUam-ii, Mont, was named from specimens of the mildew 

 on Yerhascum, rnontanum, collected at Milan by Balsamo and referred 

 by him to Oidium tuckeri. Berkeley f first published the species using 

 Montague's manuscript name, and recorded its occurrence in England 

 on Verbascum, nignlm, and also to this species referred the mildew 

 which was at one time abundant and injurious upon the Culhill's Black 

 Prince Strawberry in the Kew Gardens. J In 1880 it appeared in 

 abundance in England on turnips § for the first time though it had been 

 observed there before that time. 



During the autumn of 1893 the present writer observed it on turnips, 

 Japanese cabbage and Scotch green curled kale at Ithaca, N. Y., and 

 in the autumn of 1889 at Auburn, Ala., upon ruta bagas. 



*See Syll. Fvmg. Vol. IV, p. 41. f Ann. Nat. Hist., Vol. XIII, 1854, p. 463. 

 tOard. Chron. Apr. 15, 1854, p. 283. §Gard. Chron. XIV, 1880, p. 392. 



