ARBORICULTURE. 379 



suitably prepared and adapted to the species of tree, pruning will 

 be found but of small efficacy. 



It was supposed that when branches are taken from a tree, so 

 many organs of waste are cut off; and it has been practically 

 insisted upon that, by the removal of large branches, the supply 

 of sap and nourishment which went to their support would go to 

 a proportionate increase of the stem. From what has already 

 been stated respecting the course and movement of the sap, it 

 may be unnecessary to add that this opinion is erroneous in 

 principle, and that when a branch is cut off a portion of nourish- 

 ment to the stem is cut off also specifically from that part of it 

 which lies between the origin of the branch and the root, 

 downwards to the root. Every branch of a tree, of whatever 

 size it may be, not only draws nourishment and increase of 

 substance from that part of the stem which stands under it, and 

 from the roots, but also supplies these with a due proportion of 

 nourishment in return, and by which their substance is increased. 

 If the branch, whether large or small, acted merely as a drain on 

 the vessels of the stem, and that the sap it derived from it was 

 elevated to the leaves of the branch, and from thence returned 

 no farther than to the origin or point of its union with the stem, 

 then the above opinion would be correct : on the contrary, 

 however, when it is found that the existence and increase of 

 every twig, branch and leaf, depends on a communication with 

 the root, and that this communication passes through the stem 

 downwards to that organ, and from it upwards periodically, and, 

 moreover, that every periodical series of new vessels thus formed 

 in the branch has a corresponding series of vessels formed in the 

 stem from its point of emitting the branch to the root, it is clear 

 that a branch not only increases in substance by the functions of 

 its own organization, but must, of a necessity, periodically 

 increase the substance or diameter of the trunk. 



The results of practice agree with this ; for if an overgrown 

 limb or branch of a free-growing tree be pruned off, the annual 

 increase of the diameter of the stem is not found to exceed its 

 previous rate of increase ; or the excess, if any, is not equal to 



