CH. VIII.] THE DISEASES OF PLANTS. 289 



most essential organs of nutrition, the leaves, of the 

 weakened plant, would promote and accelerate the 

 disease. These, reduced in number and size, do 

 not properly elaborate the sap ; and I have always 

 found that, under such circumstances, these stimted 

 organs exhale the aqueous particles of the sap veiy 

 abmidantly, whilst their power of absoi-ption is 

 greatly reduced. The sap, thus deficient in quan- 

 tity, and increased in acridity, seems to corrode, 

 and affect the vascular system of the tree in the 

 manner already described. 



These facts afford us most important guides in 

 attaining the desired objects, the prevention and 

 cure of the disease. 



If superluxuriance threaten its introduction, the 

 best remedy is for the cultivator to remove one of 

 the main roots of the tree, and to be particularly 

 careful not to add any fertile addition to the soil 

 ^^ithin their range. On the contraiy, it will be 

 well if the continued exuberant gro\\1;h shews its 

 necessity for the staple of the soil to be reduced in 

 fertility by the admixture of one less fertile, or even 

 of drift sand. 



If there be an excess of branches, the saw and 

 the pruning knife must be gradually appHed. It 

 can be only trees of very weak vital powers, such 

 as is the golden pippin, that \\ill bear the general 

 cutting of the annual shoots, as pursued by Mr. 



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