51 



the strong shoots of these totally destroyed by it, 

 when the old trees growing in the same orchard, and 

 from which the grafts had been taken, were nearly 

 free from the disease. The latter have ceased to grow 

 larger, bnt continue to grow well, if not of very old 

 kinds of fruits. The young stocks, by affording the 

 grafts a preternatural abundance of nourishment, seem, 

 in this instance, to have brought on the disease ; and 

 Mr. Knight states that he always found that trans- 

 planting, or a heavy crop of fruit, which checked the 

 growth of the tree, diminished its disposition to canker. 

 In middle-aged trees of very old kinds a succession of 

 young shoots is annually produced by the vigour of 

 the stock, and destroyed again in the succeeding 

 winter : the quantity of fruit these produce is, in con- 

 sequence, very small. In this disease something more 

 than a mere extinction of vegetable life appears to take 

 place. The internal bark bears marks of something 

 similar to erosion, and this Mr. Knight originally 

 believed to be the first seat of the disease ; but sub- 

 sequent observation satisfied him that the canker is a 

 disease of the wood, and not of the bark, and led him 

 to the conclusion that canker is never a primary or 

 merely local disease, but arises from the morbid habit 

 of the plant, and to be incurable by any topical appli- 

 cation. {Knight on the Apple 3 10.) 



This last opinion is very contrary to the opinion of 

 the mere empirical gardener; for, whatever may be the 

 e 2 



