57 



lated from a knowledge of the amount of the saline 

 constituents in the healthy sap, whereas in its diseased 

 state these are much and unnaturally increased. We 

 once were of opinion, that this disease does not arise 

 from a general diseased state of the tree, but that it 

 is brought on by some bruise or injury, exasperated 

 by an unhealthy sap consequent to an unfavourable 

 soil, situation, and culture ; but more extensive and 

 more accurate examinations convince us that the 

 disease is in the tree's system; that its juices are 

 vitiated ; and that disease will continue to break out 

 independent of any external injury, so long as these 

 juices continue peccant and unaltered. This conclu- 

 sion will be justified, we think, by the preceding facts, 

 as well as by those distributed through the following 

 pages. 



The disease is not strictly confined to any parti- 

 cular period of the tree's age. We have repeatedly 

 noticed it in some of our lately introduced varieties 

 that have not been grafted more than five or six 

 years; and a writer in the Gardener s Magazine, vol. 

 5, p. 3, states, that the trees in his orchard, though 

 " only of four years' growth, are sadly troubled with 

 the canker." Although young trees are liable to 

 this disease, yet their old age is the period of existence 

 most obnoxious to its attacks. It must be remem- 

 bered, that this is not consequently a young tree 

 which is lately grafted. If the tree from which the 



