280 DISEASES OF VEGETABLES. 



the sore, prevent the efforts of nature to heal it up, 

 till at last the branch on which it appears is destroyed. 

 Partial attacks are sometimes cured by cutting away 

 the diseased parts and applying plasters of grafting 

 wax, or of cow-dung, clay, and urine. 



That the taint of canker spreads from its first 

 visible station, is very apparent to the operator when 

 cutting out the infected part. The principal sap 

 vessels are tinged with a brown unhealthy colour for 

 a considerable distance from the first seat of the dis- 

 ease ; all which contaminated organs must be cut 

 away before a cure can be effected. 



Canker is more frequently seen on orchard fruit 

 trees than on others. Among forest trees the ash 

 and elm suffer most. It is invariably found, that the 

 most luxuriant growing trees are more subject to the 

 attack than such as are of moderate growth ; and 

 those on dry sound situations, less liable than such 

 as stand in wet soils where the drainage is imperfect. 

 Low sheltered situations, where there is not a free 

 and constant ventilation, also appear to invite this 

 disease. 



This being the history of the distemper, it is quite 

 obvious that no topical application can be effectual 

 as a cure. If the poison be taken in by the root, 

 from pernicious qualities in the soil, or if generated 

 by unwholesome air, these circumstances must be 

 changed before the attack of canker can be averted. 

 Shallow planting, perfect drainage, and the application 



