Trees for Timber. 383 



forest trees, care must be taken not to over-prune (which would 

 injure the growth of the plant), never leaving less than three tiers 

 of branches untouched, and in exposed sites four tiers may be 

 left. If they are gone over every two years, it will not be 

 necessary to take off more than two tiers of branches at a time ; 

 the best season for this operation is in the spring, some weeks 

 before the sap is in motion : let it be done close and smooth, and 

 continued until a sufficient length of stem is obtained. In thin- 

 ning these plants, particularly in exposed situations, there is 

 some danger, and it ought to be proceeded in with caution. 

 These trees having thick tops, long stems, and being shallow- 

 rooted, the wind acts upon them with great force ; and when an 

 opening is made, either by plants dying, or by being injudiciously 

 thinned out, much damage is likely to ensue. To keep the tops 

 free from intermingling, yet not so much so as to introduce a 

 current of air, is the safest practice. By thus proceeding, each 

 plant, as in the case of deciduous trees, will have the means of 

 fully imbibing by its leaves, and perspiring away the crude part 

 of the sap, to make room for a succession. Having guarded 

 against the wind by moderate thinning, it becomes expedient also 

 to attend to the outsides of the plantation, to prevent its inroads 

 there, by leaving the outside plants unpruned ; which will not 

 only give warmth and security, but will present a better appear- 

 ance, by concealing the naked stems within. 



The leaves of trees seem destined by nature to perform two 

 essential functions : first, strongly to inhale, during hot and dry 

 weather, moisture from the atmosphere during the night, in order 

 to repair the waste occasioned by the perspiration of the preced- 

 ing day ; and, secondly, to receive the juices propelled to them 

 from the root, and, as secreting organs, to prepare and elaborate 

 the sap so received, to fit it for the support and enlargement of 

 all the woody parts of the plant. Hence every branch, according 

 to its size, after appropriating to its own use what is necessary, 

 sends down the residue to the stem and roots for their enlarge- 

 ment, as well as for the multiplication of the roots; which may 

 be proved from the roots of every tree being in the ratio of its 

 branches. Thus every part of the plant acts and reacts : the 

 branches are augmented by the roots, and the roots by the 

 branches. 



Pontey and some others consider that the principal use of 

 the leaves is to attract the sap upwards; and that tapering stems 

 are occasioned by branches obstructing the ascent of the sap, 

 and also- applying it to their own use ; thus preventing the en- 

 largement of the stem upwards : so that, according to their ideas, 

 if the lower branches are removed, a greater portion of sap will 

 go to the enlargement of the stem above. The author of these 

 observations believes the reverse to be the fact, and that the 



