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ROYAL HORTICULTURAL SOCIETY. 



canker. Something, indeed, of this kind had already been tried by 

 Mr. Knight ; but it was certainly most desirable that the experi- 

 ment should be confirmed, whether Mr. Pearson was acquainted 

 or not with what had been done previously. 



There can be little doubt that the main cause of Canker is 

 penetration into an un genial or badly drained soil, and a fre- 

 quent lowering of temperature in consequence of the presence 

 of constant wet ; but in many cases a naturally weakly consti- 

 tution must be taken into account, which gives way under rapid 

 alternations of cold and heat. In no case, I believe, is any para- 

 sitic fungus concerned, though, where branches have perished from 

 Canker, such fungi as Tulercularia vulgaris, Spliceria ambiens, &c. 

 often make their appearance, and are occasionally considered the 

 cause rather than the consequence. 



The different forms which Canker assumes do not very readily 

 admit of classification. The most convenient plan will probably 

 be to consider separately those which affect each particular tree 

 or group of trees. I begin, therefore, with those which occur on 

 Apple-trees, of which there are several varieties. 



1. One of the most common forms of Canker in Apple-trees is 

 that which is produced by the woolly Aphis. The little insect 

 gains admission generally at the base of a young shoot or bud, 

 and by constant imbibition of the juices and consequent irritation 

 causes an irregular growth, accompanied by a greater or less decay 

 of the tissues, so that in a short time a ragged hollow is produced ; 

 and where these hollows are scattered over the whole tree, the fer- 

 tility is greatly impaired, and death at length ensues. The 

 common Codlin is perhaps more subject to this form of Canker 

 than any other variety. A careful inspection will enable the cul- 

 tivator frequently to arrest the evil in an early stage. I have 

 found nothing so effectual as the common mixture of grease and 

 tar which is applied to horses' hoofs ; if this be rubbed in carefully 

 with the finger, the evil will in general be arrested. Where, how- 

 ever, it is of long standing, it may be more difficult ; and even if the 

 insect is destroyed, the diseased tissues may taint those beneath, 

 and the malady will thus continually burrow deeper and deeper. 



2. A second form of Canker, to which the Keswick Codlin is 

 peculiarly subject, at first sight appears very similar to this, but 

 on close inspection it will be found to be of a totally different 

 nature. Probably from something wrong about the roots, a quan- 

 tity either of adventitious buds or roots are produced in little 

 shield-like patches. If buds, they are undeveloped ; if roots, the 



