102 GENERAL PRINCIPLES. 



whole. We prime to induce fruitfulness, and to diminish 

 it. We prune in the growing as well as in the dormant 

 season, and, finally, we prune both roots and branches. 

 Thus we see that pruning is applied to all parts of the 

 tree, at all seasons, and to produce the most opposite 

 results. 



It appears necessary to treat of pruning, under each of 

 these circumstances, separately. 



1st. Pruning to direct the Growth from one part of 

 a tree to another. The first period in the existence and 

 growth of a tree in which this becomes necessary, is in 

 the nursery. Those who have had any experience in tree 

 culture, have observed that young trees in nursery rows 

 have a tendency to increase in height without acquiring a 

 well-proportioned increase in diameter. In certain cases, 

 this want of proportion becomes so great, that the tree 

 bends under its own weight, and hence it is necessary to 

 resort to some method of propping it up. This condition 

 is attributable to several causes. First, the absence of a 

 sufficient amount of air and light around the stem, to 

 enable the leaves on it to fulfill their functions properly. 

 It has been shown that the formation of new wood de- 

 pends upon the elaborating process carried on in the 

 leaves, and that this process can be maintained only in a 

 free exposure to the sun and air. This being the case, it 

 is obvious that any part of the tree excluded from the 

 action of these agents cannot keep pace in growth with 

 other parts to which they have full access. In nursery 

 rows, as trees are usually planted, the stems, after the 

 first year's growth, are to a great extent excluded from 

 the light, consequently the buds and leaves on them can- 

 not perform their parts in the creation of new wood. The 

 top of the tree, however, is fully exposed, and, conse- 

 quently, it makes a rapid growth towards the free air and 

 light. When this is continued for two or three years in 

 succession, the tree becomes top-heavy; the quantity of 



