DISEASES OF ROSES 91 



on the peach, apricot, almond, and cherry-laurel until Woronichin 

 (9) proved it to be confined to the rose. 



Symptoms. The first signs of the disease are grayish or whitish 

 spots on the young leaves and shoots. Frequently, the unopened 

 buds are white with mildew before the leaves are affected to any 

 great extent. These spots quickly enlarge, a felt-like coating of a 

 white, powdery appearance being commonly found on the stems 

 and thorns. Later the mildew appearance is less conspicuous or 

 entirely lost, the affected areas turning black. 



Dwarfing, curling and various deformations of young leaves, 

 stems and buds occur. Injured leaves may fall, and the leaf sur- 

 face of the plant may be greatly reduced. Growth and flower 

 production is materially interfered with, young buds being fre- 

 quently attacked and rendered entirely worthless. 



Etiology. 



Powdery mildew is caused by the fungus Sphaerotheca pannosa 

 (\Yallr.) Lev. rosae Wor. 



Identity. The fungus was first reported by "Wallroth^ under 

 the name of Alphitomorpha imnnosa. Subsequently the fungus 

 was called Eurotinm rosarum by Greville,- Erysibe panJiosa by 

 Schlechtendahl ^ and Link,* and Erysiphe pannosa by Fries.^ 

 Leveille ^ transferred the fungus from the genus Erysiphe to 

 Sphaerotheca. 



Salmon (7) states that roses in America are attacked by two 

 species of fungi, viz., Sphaerotheca pannosa and S. humili and that 

 the American fungus which has passed under the name of S. 

 pannosa is for the most part S. humili. He had seen onlj' two speci- 

 mens of true S. pannosa from America. Stewart (8) reports several 

 cases of rose-mildew in which the fungus was unquestionably' S. 

 pannosa. 



1 Wallroth, K. F. W. Naturgeschichte des Mucor Erysiphe L. Berl. Ges. Nat. Freunde 

 "Verhandl. 1:6-45. 1819. 



' Greville, R. K. Scottish Cryptogamic Flora 3: pi. 164. fig. 2. 



3 Schlechtendahl, D. F. L. von. Flora Berolinensis 2: 168-170. 1824. 



«Lmk, H. F. Willdenow, Species Plantarum 6: 104. 1824. 



' Fries, E. Systema Mycologicum 3: 236. 1829. 



« Leveille, J. H. .\nn. sci. nat. Ill, 16: 13S, pi. 6, fig. 8. 1851. 



