observed this same species feeding on the exuding sap of can- 

 kered limbs and stubs. That it may carry the bacteria to the 

 crotches seems obvious. Besides this, many of the crotches are 

 of. such form that they readily retain moisture and thus afford 

 the best of conditions for bacterial growth. 



How the Disease Affects the Tree. 



The effect of the canker on the tree is to lower its vitality to 

 a greater or less degree by cutting off the food supply to the 

 roots, and thus indirectly reducing the flow of sap to the branches 

 and leaves. The " collar rot " and- " crotch cankers " seem to be 

 the most fatal to the tree. The effects of the canker are first 

 evidenced in the foliage. If there is a large body canker, the en- 

 tire tree may show the effects of the trouble. More often the first 

 symptom noted by the grower is the peculiar appearance of the 

 foliage on one or more of the limbs. Either these branches fail 

 to leaf out at all in the spring, or if they do, the leaves never fully 

 expand but remain undersized and curled or inrolled. They never 

 take on the dark green color of healthy foliage, but remain pale 

 and gray. Growers often refer to such trees as having " mouse 

 ear " leaves. As the season advances and the cankers spread, 

 the leaves often die and dry up on the branches. Sometimes 

 badly infected trees may live for two or three seasons, but such 

 trees have scanty foliage, blossom profusely and frequently set 

 a heavy crop of fruit, which falls prematurely or is small and 

 inferior in quality. 



As I have already pointed out, small cankers may not of them- 

 selves seriously affect the health of the trees. When the trees 

 are strong and vigorous they frequently succeed in promptly 

 healing the wounds. The dead bark of the canker, however, 

 makes an excellent infection court for the entrance into the tree 

 of " heart rot " and decay-inducing fungi. Moisture, so necessary 

 to the germination and growth of the spores of fungi, is retained 

 for a considerable time in the dead tissue. This is more especially 

 true of crotch cankers. No doubt these rot fungi are often to 

 blame for the final death of the tree. The heartwood of badly 

 affected limbs and trees is commonly found to be. soft and rotted, 

 with only a thin rim of sound sap-wood surrounding it. 



