212 



Diseases of Economic Plants 



the leaves, similar oval spots, 3-10 mm. in diameter, with 

 the pycnidia usually in concentric circles, are abundant. 

 The lower, older leaves are affected first, resulting in their 

 death. The younger leaves die 

 later. Stems are subject to the 

 same attack — first near the 

 ground, later upon all parts; the 

 spots often penetrating through 

 the woody part, thus causing 

 wilting and death of the parts 

 beyond. The stem attack is the 

 most serious form, since it di- 

 rectly causes death to a large 

 part of the plant. This is espe- 

 cially true if the disease be fol- 

 lowed by dry weather. 



All forms of the disease tend to 

 decrease the yield in proportion 

 to their prevalence. Plants not 

 Ivilled before flowering may de- 

 velop pods, though of lessened 

 yield. 



Disease upon the pod may 

 penetrate completely through it 

 and appear upon the opposite 

 side, or more frequently it may 

 grow into the seed within the 

 pod. Seeds badly diseased in 

 this manner adhere to the pod; 

 if less affected, they thresh out, 

 according to the color of the 

 variety, more or less discolored spots. Often seeds are 

 diseased, and yet so slightly disfigured as to escape ob- 

 servation. 



Trial has demonstrated that of badly infested seeds only 

 6 per cent are capable of germination, and that even when 

 they do germinate, the resulting plants seldom reach ma- 



FiG. 115. — Spotted pods of 

 French June field pea. 

 After van Hook. 



are shrunken, and show. 



