144 THE FRUIT-TREE AND SHRUB PRUNER. 



formed below, towards which a natural current of sap 

 flows, and it is a difficult thing to prevent this when once 

 it is thoroughly established. It sometimes proves 

 almost death to the trees to remedy this one evil, and 

 it all arises from the mutilation of the roots by digging. 



The Canker, or Gangrene. — This is a troublesome 

 and in some cases a fatal disease. Some think it is 

 caused by atmospheric influences, while others attribute 

 it to the unsuitable state of the soil, and others again 

 to the overgrowth of the branches. It seems rather 

 difficult to determine which is the true cause, since not 

 every variety of the same species is affected alike, 

 although growing side by side. For instance, the 

 Hawthornden Apple suffers more from this disease than 

 most other Apple-trees ; while some equally as delicate 

 in character and growing upon the same spot escape, 

 this sort generally gets it. Now, if it arose from 

 atmospheric causes all would suffer more or less ; if it is 

 constitutional, then no one instance would be found 

 exempt from it, which is not always the case, there 

 being some instances in which no gangrene attacks 

 this kind. 



In my opinion, canker, or gangrene on trees arises 

 not from anything in the air, nor from overgrowth, nor 

 from pruning alone, but chiefly from the disagreement 

 that exists between the state of the roots and the con- 

 dition of the atmosphere ; for instance, if the subsoil is 

 too cold. It is something like a person living in a 

 locality consisting of a cold clay, and which holds 

 water, causing rheumatism and at the same time aggra- 

 vating his appetite. The subsoil being so much below 

 the heat of the air, and the roots not being in active 

 operation with the demands of the branches, a weaken- 

 ing power exists among them, and, as a matter of course, 

 those channels that are the weakest sutler first ; hence 

 a limb here and a limb there fails, there being perhaps 

 some minor defect previously in that particular part, 

 which becomes suddenly paralyzed, and, as a rule, gets 

 beyond remedy. A bruise with the hammer, or a nail 

 pressing against the branch, will produce the like effect, 



