1*4 



FUNGOUS DISEASES OF PLANTS 



very short period of growth. Nevertheless, under conditions 

 more favorable for the host plant the blight may never extend 

 more than a few inches, resulting merely in a tip pruning. In 

 the case of the apple this twig blight is the rule, the disease 

 apparently being usually unable to maintain itself in the larger 

 branches. Young fruits of the apple, an inch in diameter, are 



FIG. 32. WATER SPROUTS OF APPLE KILLED BY BLIGHT 



frequently affected ; and the copious growth of the organism 

 gorges the fruit with the slime which may be exuded in droplets. 

 The progress of the disease is ordinarily very clearly indicated 

 by the appearance of the bark. The growth of the organism 

 within the tissues of the soft bark causes a water-soaked appear- 

 ance, and finally a blackening and shriveling. The organism 

 may, however, extend to a distance of several inches, or even 

 a foot, below the water-soaked area. When the organism ceases 

 to spread rapidly in the tissues, a sharp line of demarcation is 

 noticeable, separating the dead from the healthy or comparatively 



