KXPEKIMENT STATION l.'EFOKT. 523 



is found in Eurnpo, Asia, Ja])an and the I'nited States. iSpivruihcca 

 phytoptoptrylla K. & S. is a reeently-discovered American species, 

 described in 1888, which has been fotind only uj^on the hackberry 

 (Celtis occidentalis) and only associated with the distortions of the 

 branches due a gall mite (Phijtoptus). This limitation contrasts 

 greatly with Erysiplie Cichoracearum DC, which is a world-wide 

 species, described with its present scientific name in 1805, thriving 

 upon a long list of hosts. For example, in the United States it has 

 been found upon 105 species of plants. It is this species that mil- 

 dews the ragweeds, asters and goldenrods in the fields and neglected 

 land, and the dahlia, sunflower and cucumber among cultivated 

 plants. The Microsphcera Alni (Wallr.) is an old species, with a very 

 wide range of hosts in sixteen different families of plants, usually, 

 however, upon trees or shrubs. This species has been mentioned in 

 the opening paragraph as the mildew of the lilac. It is quite gener- 

 ally upon the nut trees, birches and has a special liking for the dog- 

 woods and viburmmis. Having such a long list of hosts, it is not 

 surprising that it is met with in Europe from Italy to Xorway, as 

 it is with us from Maine to California and Manitoba to the Gulf. 



Po'wdery Milde\(rs of the Orchard. 



The leading powdery mildews of the orchard are Spcvrotheca jian- 

 nosa Wallr., which grows upon the peach, and Podosphara oxyacanilice 

 (DC.) DBy. upon apple, cherry and pltmi. The mildew of the peach 

 is not very common, but has been abundant the present season. It 

 appears upon the young twigs and their younger leaves, covering all 

 with a thick, white coat, while the leaves are prevented from making 

 their normal growth and are sometimes distorted, suggesting the 

 work of the leaf-curl parasite, which, however, is a very different 

 fungus. The peach mildew is found upon only a few species of 

 plants, the roses being the chief of these, and the subject will be con- 

 sidered again in this paper. 



The mildew of the apple, plum and cherry is, in appearance, similar 

 to the one of the peach, but very much more common and destructive. 

 It is most frequently met with upon the cherry, the young leaves of 

 which in autumn are often whitened with it and more or less dwarfrd 

 and distorted. Young trees seem more disposed to the mililow tliim 



