434 



BUSH-FRUITS 



are soon attacked in the same way and partially or entirely 

 checked in their growth, being rendered wholly unfit for use in 

 most cases. It first appears as a patch of cob web -like threads, 

 which soon form a dense mat and become white and powdery 

 from the development of white conidial or summer spores. These 

 are produced in immense numbers, and are readily blown about 

 by the wind, to contribute to the further spread of the disease. 

 A few weeks later the winter spores, or ascospores, begin to 



'Fig. 78. Mildew on a young shoot. 



develop. These are contained within chestnut -colored perithecia, 

 which give a dirty brown appearance to the affected parts. These 

 spores remain over winter within the protecting perithecium and 

 germinate in spring, thereby spreading the species the succeed- 

 ing year. 



This disease, unlike many other fungi, seems to develop best 

 in dry, hot climates, and for this reason causes much more 

 trouble in America than in England. It is less serious in the 

 northern portions of the United States and in Canada than 

 farther south. Many English varieties or their seedlings have 



