94 PLANT DISEASES 



below following suit ; at the same time new conidia are 

 being produced at the base of the chain. This formation 

 of numerous chains of upright conidia gives to the patches 

 a minutely powdery appearance, hence the popular name. 

 Myriads of conidia are produced throughout the summer, 

 and being washed by rain on to the surface of healthy 

 portions of the vine, where they germinate at once, the 

 disease spreads rapidly. 



Towards the end of summer a second and higher form 

 of fruit develops on the patches of conidia-bearing 

 mycelium, first appearing as yellow points, which finally 

 change to black. These bodies are called perithecia, and 

 are hollow spheres, containing in their interior spores pro- 

 duced in asci. The perithecia are provided with several 

 spreading appendages or branches, each of which is more 

 or less spirally curved at the tip. The ascospores are 

 liberated from the perithecia in the spring, when they 

 germinate and give origin to the conidial form of the 

 fungus. The conidial form of the fungus was the only one 

 known in Europe until quite recently, when the perithecia 

 were observed in France. 



Preventive Means. — According to Professor Galloway, 

 the disease is easily checked. ' It succumbs readily to 

 sulphur, either in the form of flowers of sulphur, or solutions 

 of the sulphide. In applying the sulphur, bellows should 

 be used, and the first applications should be made ten or 

 twelve days before the flowers open, the second when in 

 full bloom, and a third three weeks or a month later, if the 

 disease seems to be on the increase. The best results are 

 obtained with the thermometer ranging from 80° to 100° 

 F. In this temperature fumes are given off which quickly 

 destroy the fungus. We have obtained excellent results in 



