Blight Canker of the Apple Tree. 



189 



the cankers spread, the leaves often die and dry up on the branches (Fig. 

 6;^,). Sometimes badly affected trees will pull through until autumn or 

 even live for two or three seasons. Such trees have scanty foliage, blos- 

 som profusely and frequently set a heavy crop of fruit. This fruit falls 

 prematurely or is small and inferior in quality. Fig. 64 shows a large 

 body canker at the base of one of the main limbs on an old tree. The 

 canker had nearly girdled the limb. 

 This spring the branch was loaded 

 with blossoms to the exclusion of 

 foliage, while the other limbs of the 

 tree bore a normal quantity of 

 flowers and leaves. Such affected 

 limbs and trees, as if in anticipation 

 of their approaching death, seem to 

 devote their expiring energy in one 

 grand and final effort to reproduce 

 themselves. 



As I have already pointed out, 

 small cankers may not of them- 

 selves seriously aft'ect 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 excel- 

 lent infection court for the entrance 

 into the tree of " heart rot " an:l 

 decay-inducing fungi. ]\Ioisture, so 

 necessary to the germination and 

 growth of the spores of fungi, is re- 

 tained for a considerable time in the 

 dead tissue. This is more espe- 

 cially 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 com- 

 monly found to be soft and rotted, t?,^ at u j -t u 



•' ^ ^^ , J, jQ gj — Large body canker near base 



with only a thin rim of sound sap- of tree, often referred to as "collar 



wnnd QnrronnfUno- ?f ^''^•" The tree has made repeated at- 



woocl surroundmg it. ^^^p^^ ^^ j^^^^ ^^-^ wound. 



