2 5 



FUNGOUS DISEASES OF PLANTS 



that portion of a limb bearing a side branch. It may arise inde- 

 pendently, or near an old knot. As the swelling increases in size 

 the bark is broken and the stroma of the fungus then becomes 



FIG. 1 08. PLOWRIGHTIA MORBOSA, BLACK KNOT OF PLUM. (After Longyear) 



evident. By midsummer the knot will have attained full size, and 

 from that time until the winter, or as long as the remnants of the 

 knot may persist, it will be deep black and carbonaceous in tex- 

 ture (Fig. 1 08, a). In the case of small twigs which are affected, 

 bending may be caused, so that a right angle will be made from 



