It appears, then, that while cultivation accelerates the period of fruit-bearing and perfects the fruit, it is also accompanied with premature age and liability to diseases. We do not wish to be understood as opposing the habit of _cultivating_ fruit, or as prejudiced against grafted varieties—we are neither opposed to the one nor to the other. But we would deduce from facts, some conclusions which will enable us to perfect our fruits by a more discriminating treatment.
The question will arise, Is it only by accident that liability to disease increases, with increase of cultivation? Is there an _inherent_ objection in _all_ artificial treatment? or is there objection only to particular methods of artificial cultivation?
Although there may be too many exceptions, to allow of our saying, that quickly-growing timber is not durable, it may be said in respect to trees of the same species, that the durability of the timber depends (among other things) on the slowness of its growth. Mountain timber is usually tougher and more lasting than champaign wood; timber growing in the great alluvial valleys of the West, is notoriously more perishable than that grown in the parsimonious soils of the North and East.
The reason does not seem obscure. In a rich soil, and under an ardent sun, not only is the growth of trees greater in any given season, than in a poor soil, but the growth is coarser and the grain coarser. But what is a _coarse_ growth, and what is fine-grained, or coarse-grained timber?—timber in which the vascular system has been greatly distended, in which sap-vessels and air-cells are large and coarse. Where wood is formed with great rapidity and with a super abundance of sap, not only will there be large ducts and vessels, but the sap itself will be but imperfectly elaborated by the leaves. We may suppose that overfeeding in vegetables is, in its effects, analogous to overfeeding in animals. The sap is but imperfectly decomposed in the leaf—it passes into the channels for elaborated sap in a partially undigested state—it deposits imperfect secretions, and the whole tissue resulting from it will partake of the defects of the _proper juice_.[12]
Thus a too rapid growth not only enlarges the sap passages, but forms their sides and the whole vegetable tissue of imperfect matter. This accounts, not only for the perishableness of quickly-grown timber, but, doubtless, for the short-lived tendency of cultivated fruit in comparison with _wildings_. For where the tissue is imperfectly formed, general weakness must ensue.