As the tree advances in growth, and approaches toward its natural period of maturity, it is supposed that there is an accumulation of nutritive matter within it, and at the same time the roots will have exhausted the soil, to some extent, of the elements that contributed to the production of wood-growth, and the result is the formation of flower-buds. Now it becomes a nice matter to preserve the proper balance between these two systems of growth, the wood producing and the fruit forming. Two opposite systems of production have become established in the tree, the one infertile, the other producing the desired fruits; the one preserving the health and vigor of the tree, the other tending to preserve the species at the same time that it satisfies our demands for fruit, but also meanwhile tending to the destruction of the tree, for all old trees are apt to overbear. Young trees, on the contrary, in which the vigor of wood-growth remains in full activity, very often produce fruit-buds and blossoms, but do not perfect their fruit, which either fails to set, from some imperfection of the organs of reproduction, or falls prematurely, in consequence of the wood system absorbing the nutriment, or failing to prepare the proper juices for their support. Trees, in these different conditions, require an entirely opposite treatment. The younger need summer pruning and pinching, to check their too great vigor, and to develop the laterals or spurs with their blossom buds; the older need winter pruning, for the double purpose of reducing the amount of fruit, and also to excite renewed vigor in the production of wood growth that shall take the place of that which has been removed. This subject will be more appropriately discussed in another chapter, to which the reader is referred; while we proceed to the legitimate topic of thinning fruit.