GO A Monograph of the Erysiphaceae 



Myc. 86, Wint. in Rabenh. Krypt. Fl. Deutschl. i-: 34. It is prob- 

 able that this fungus is S. huDudi, as this species occurs on sev- 

 eral American species of Rubles, The record of '' ^. Castagnef 

 on the vine probably rests merely on the occurrence of '' Oidium 

 Tuckeri'' on the plant, as the latter was supposed by Fuckel 

 and others, to be a conldial form oi '' S. Castagneiy 



S. Junmdi^ when it occurs on hops, is well-known as ** hop 

 mildew," a disease which causes serious injury in hop-gardens. 

 On the leaves, the fungus does not occasion much damage, prob- 

 ably only slightly weakening the vitality of the host-plant, but 

 when it occurs on the cones it materially injures their quality, and 

 in severe attacks causes them to completely shrivel up. The 

 "hop mildew/* although recorded on cultivated hops on the Con- 

 tinent in many places, does not apparently cause so much damage 

 there as In England, where it is one of the most dreaded diseases 

 of the hop-grower. In the United States, also, although Burrill 

 (60, p. 6) says that 5. hiunidi ''is a very destructive parasite, es- 

 pecially on cultivated hops " the disease would appear, judging 

 from the absence of any reports (which have been so much made 

 by American mycologists on other plant-diseases) to be less prev- 

 alent or less severe than in English hop-gardens. As in the vine 

 powdery mildew, sulphur has been found to be an efficacious 

 remedy. The best results have followed from the use of flowers 

 of sulphur applied during sunshine. For full details of the prepar- 

 ation and application of the sulphur reference may be made to the 

 papers of Whitehead (392, 393) on the subject. 



I cannot confirm the statement made in the Journal of the 

 Board of Agriculture for 1897 (181) that in hop-cones infected by 

 S. Jiumidi the mycelial hyphae penetrate into the epidermal cells 

 of the bracts, as in material examined I have found within these 

 cells only the usual haustoria. 



Whitehead (393, p. 247) recommends as a preventive method 

 agamst the hop-mildew the removal of all other plants which are 

 the hosts of the fungus from the hop-gardens, and mentions espe- 

 cially Taraxacum^ Scnccio vidgaris and other Composites, and 

 Planiago, These host -plants of the old aggregate species '' S. 

 Castagnd'' all belong, however, to the form now separated as S. 

 hiiundi, wdiV. fuliginea, while the hop-mildew is caused bv the tvoe 



