CH. Yin.] THE DISEASES OF PLANTS. 283 



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 con- 

 vince- me that the disease is in the tree's system ; 

 that its juices are vitiated; and that disease ^ill 

 continue to break out independent of any external 

 injur}% so long as these juices continue peccant and 

 unaltered. This conclusion will be justified, I think, 

 by the preceding facts, as well as by those distributed 

 through the following pages. 



The disease is not strictly confined to any par- 

 ticular period of the tree's age. I 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. V. p. 3, states, that the trees in his orchard, 

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

 \sith 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 

 remembered, that that is not consequently a young 

 tree which is lately grafted. If the tree from which 

 the scion was taken be an old variety, it is only the 

 multiplication of an aged individual. The scion may 

 for a few years exhibit signs of increased vigour, 

 owing to the extra stimulus of the more abundant 



