OF TRAINING. 265 



The foregoing are the principal advantages which 

 arise from training plants ; let us next consider what 

 disadvantages there may be. The only trees which 

 at all approach in nature the state of trained plants are 

 climbers and creepers, whose stems, unable to support 

 themselves, cling for a prop upon whatever they are 

 near ; some of them enclose the stem of another plant 

 in their convolutions ; others simply attach themselves 

 by means of tendrils as the Vine, by hooks as the 

 Combretum, or by other contrivances; and some, 

 like the Ivy, lay hold of walls, rocks, or the trunks 

 of trees, by their minute roots. To none of these 

 can that motion be necessary to which plants are 

 naturally exposed, and which, as has been already 

 seen (p. 157), is of so much importance to the healthy 

 maintenance of their functions. Hence it is, that 

 among fruit trees the Vine never suffers from being 

 trained : indeed its anatomical structure is especially 

 suited to such a mode of existence ; while all erect 

 trees, of whatever kind, whose branches nature 

 intended to be rocked by the storm, and perpetually 

 waved by the currents of air to which they are 

 exposed, in all cases suffer more or less. 



One of the commonest and worst diseases induced 

 by training is a gradual impermeability of tissue 

 to the free passage of sap, which appears to stagnate, 

 so that in time the branches become debilitated and 

 juiceless ; the obstruction to the flow of the sap 

 tends to produce coarse shoots from various parts of 

 the branches, and especially from the roots. The 

 cause of this seems to be the too rapid deposit 

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