DISEASES OF VEGETABLES. 289 



without injury. If the whole bark be intended for 

 defence of the stem only, and on this account pre- 

 served, it appears to be superfluous, because the young- 

 shoots, the most delicate parts of the tree, have only 

 one bark, and this we see is a sufficient protection to 

 all hardy trees ; therefore all the layers are not neces- 

 sary, as is proved by the remedy above mentioned 

 being- effectual. It is the opinion of some practical 

 men, that the chief energy or vital vigour resides in 

 the head rather than in the root of a tree, i. e., the 

 head receives from the atmosphere a maturing influ- 

 ence which alone qualifies, while it excites supplies 

 from the earth. The roots, if in good soil, however 

 old, never fail ; and, therefore, they say, if the head 

 be kept healthy, the system flourishes. To do this, 

 they recommend every feeble or dead shoot to be 

 cut off, and every layer of the old scabrous bark 

 to be periodically removed; so that every latent 

 principle of the growth be called into action, and the 

 progressive expansion of the tree encouraged. This 

 doctrine, with some qualification, we think, is not 

 injudicious. 



Pear, apple, and other fruit-trees, are the proper 

 objects for this treatment. Such as have a watery, 

 being fitter for the operation than those having a 

 gummy or resinous sap. 



