466 CANKER. 



(1) Excessive rain succeeding a long period of 

 dry weather which had hardened the sap-vessels. 



(2) Severe pruning while the roots extended 

 themselves, under high cultivation, and disturbed 

 the equilibrium. 



(3) A sudden change of temperature. 



This malady is most likely to appear first where 

 the tree has been bruised, or cut with the knife. 

 When it results from excess of moisture in the soil, 

 thorough draining is a most effectual preventive ; 

 when from improper pruning, cutting the roots will 

 restore the equilibrium ; but when from vicissitudes 

 of temperature, it is entirely uncontrollable. This 

 malady is not as common in the United States as in 

 Great Britain, but nevertheless occasionally appears. 



Mr. Berkeley says: "I have before me some 

 branches of the Golden Pippin apple, which, in the 

 living portion, is still strong enough to bear very 

 fine fruit, though the tree is evidently fast approach- 

 ing the end of its existence. The fruit appears on 

 two kinds of branches, equally fertile ; the one, tall 

 spring twigs, grown with great rapidity ; the other 

 stunted, more or less divaricate branchlets, whose 

 growth has been extremely slow. Both are equally 

 affected with canker, though not visibly, in the same 

 way ; that upon the vigorous branches apparently 

 growing downward and casting their thin bark, 

 while the other perishes first at the base, and de- 

 prives the upper parts of nutriment. On closer 



