102 



DISEASES OF ECONOMIC PLANTS 



tioned, those depending upon electrical or atmospherical 

 influences, freezing of the bark, too long culture of par- 



FiG. 42. — Pear blight ; healthy and diseased twigs. Original. 



ticular varieties, freezing of the roots, too high culture, 

 insects, fungi, and absence of needed food. One of the 



