There is, therefore, a medium between these two, by adopting which, the greatest quantity of the most valuable timber will be produced; although, at the same time, it is astonishing, when looked at from a physiological point of view, what a small quantity of foliage is required to keep a plantation tree in a healthy, growing condition, and to produce a trunk of useful dimensions. This may, however, be explained by the fact that the almost entire absence of large limbs and branches, which in some cases would amount to one-fifth the total bulk of the tree, renders the amount of sap, and consequently of leaves, required proportionately less, the nutriment being mainly elaborated in the building of the trunk. Independent altogether of the forests of northern Europe, Canada, etc., which have grown up naturally, examples might be given in our own country—the native Fir forests in the Highlands of Scotland, the valuable Beech woods on the Chiltern Hills, and a few Larch plantations in Yorkshire and Bedfordshire—where trees averaging 70 ft. in height, growing at from 4 to 6 yards apart, and with only a tuft of foliage atop, may be seen. It is only, however, by long and careful study and attention to different trees at different stages of their growth that any idea can be formed of the amount of branches and foliage required for preparing the sap that will be necessary for the profitable yearly increase of the trunk until maturity is arrived at. The questions now to be dealt with in growing timber for purely economical purposes are: (1) At what age should thinning be commenced? (2) To what extent should it be engaged in? (3) What time should elapse between each thinning? And (4) Which trees should be removed? At the outset, it may be well to mention, that in so far as any of the above questions are concerned, no hard and fast line can be laid down as to the universal management of plantations, each tract of wood, and even different parts of the same wood, according to the particular species of tree, quality of soil, altitude, and exposure, being dealt with on its own peculiar footing. Many serious mistakes have been committed, and irreparable damage done, by treating every plantation alike and according to the rule-of-thumb method. Upon the manner in which thinning is performed, much of the ultimate success of a plantation will depend, and it is a matter requiring great tact, forethought, and discrimination, which can only be acquired by long experience, and an intimate knowledge of trees and their surroundings. The quality as well as quantity of timber produced should be carefully considered in the management of every plantation. In dealing with the following questions regarding thinning, it may be well to state that the average plantation will alone form the basis of remarks.