To gain a philosophical conception of this all-important topic, requires an acquaintance with the structure of the plants we have to deal with, and limiting ourselves, for the present, to fruits, we find that the plants which produce them are with very few exceptions, of the most compound organizations - all being composed of vascular and cellular tissues, and the greater part capable of forming permanent woody fibre.

It is well known to all vegetable anatomists, that plants are composed entirely of cells, which are of different kinds, and disposed, in various ways, to build up the general structure, that through this multitude of variety the fluids and gases permeate, to support the waste and enlargement of the integral parts, and that the periodical action is kept up by the influence of heat, light, and moisture, so long as the vital principle is present with the individual. The first burst of growth after the period of rest, is nothing more than the development of these cells or structural embryo, which were formed the season previously, and accordingly as the centralization was. more or less favorably constituted, or, in other words, well, evenly, and perfectly ripened heretofore, so will the expansion be vigorous, or not, and the show for blossom be abundant and fine, or sparse and deformed. This centralization can only be obtained complete when the plant is under the most genial influences, and has the advantage of favorable circumstances. According to. the constitution of each individual species, so will these requirements differ.

One, for instance, would do with more steady heat than we generally possess, while another is better suited in a cooler climate; and taking these differences, we must readily conclude, that in neither of these two examples will there be an uninterrupted and equal formation of the required peculiar organism for another season's fruitfulness. In the former, there is a want of concentration, and, consequently, a deficiency of fruit, but abundance of leaves; and, in the latter, the cells will be too hastily formed to properly act the part for which they were destined, and the cell walls too indurated to allow the juices to flow freely, producing stunted growth, depauperated and few flowers, and small fruit, deficient in quality, having a tendency to dryness and austerity.

It is from the free and healthy action of the leaves that we must look for all ' success in fruit growing; they are the great chemical laboratories; the crude juices which are absorbed by the roots are here elaborated and changed, by the combination of gases from the atmosphere, when pure structural cells are formed. In a natural state, we find that, in fruits generally, there is more of woody fibre than in those which are cultivated; they are also situated in the climate which is adapted to their peculiarities. Here is the more hardy constitution unimpaired, and a less tendency to disease or premature decay; but, in the cultivated, we have comparatively more of the cellular, a gorged body (if the expression.may be used), which has become constitutional and hereditary; consequently, there is less hardihood to resist any unfavorable influences - hence the necessity of careful attention. In cultivated fruits, generally, we have larger and more robust leaves, which, if they be favored with uninterrupted action during their natural period, will do their full share of work in storing up the extra demand for true sap that is needed for the larger and more numerous cells, or those of a character which are suitable for the after development of fine fruit, and, in a plant of permanency, of also adding to solid bulbs.

An equipoise of root and leaf is necessary to support life, but, as the latter is the great store for maturity, it is more essential to our purpose than the encouragement of extreme extension of the roots. The pear or quince stock is an example in proof of this assertion; the roots of the quince do not extend so far away from the tree as do those of the pear; the spongioles are comparatively more numerous, but they are not capable of absorbing so much crude matter from their smaller proportions, yet they are sufficiently so to keep in health the more robust varieties for many years. In this case, the leaves are forced, as it were, to deposit the carbonized juices in the body of the tree in a more fluid state, and the downward current is arrested; and hence is composed the shorter but more plethoric growth, with an increase in fleshiness and size of the fruit.

The same causes that affect the leaf will affect the fruit also, for they are co-existing parts of the same organism, the latter being different only in having arrived at that highly concentrated state to which all vegetable action tends when the circumstances have been in accordance with the want. We shall understand by this, that at maturity, nature casts off the fruit in the same way that the leaf falls when it has fulfilled its office; but there is this difference in the two: the leaf has been forming a bud in its axil which remains behind, and attached to the parent, while each receptacle of the fruit has, in the mean time, been perfecting its bod or buds, according to the structural complexity in the centre of, or upon its own body, and which becomes an independent germ, liberated from the main body when in a fit state to develop itself. It is then evident that injury to one will likewise affect the other.

Light is tire great solidifier of the juices of plants, and the more a leaf or fruit is exposed to it, the more vascular will the progress of growth become. Now, this being the case, as the leaf has to provide for another period of development, it is requisite to expose it to all the influence of light that the plant's constitution will bear; but, in the fruit, as we want pulpiness and good flavor, we find a partial Shade the best, so far as may be consistent with the securing of sufficient saccharine matter, and the particular aroma for which some fruits are so much prized. Generally speaking, nature has provided, in her own economy, for this particular, but there are individual cases where a partial shade would improve the quality, providing it be applied so that the leaves may be exposed. This is more particularly feasible when we consider that the leaves exhale a great portion of the fluids, and pates the more solid parts into the increasing bulk of the plant, while the fruit retains nearly all that is absorbed with which to feed and mature the seed. The fleshy part of the fruit, and that for which it is valued, is a complete organization of cellular formation like all other parts, only that the cellular preponderates.

While the fruit is swelling, or increasing in size, these cells are active, and imbued with the principle of life, but, like all other parts, they have only their allotted period of existence, which extends to the ripening of the seed. After this, they become disorganized, chemical action and consequent expansion take place, and, by a beautiful arrangement of elementary particles, the carbonic principle forms sugar in solution with water, and combines with other minor products, so as to establish the varied lusciousness that is so grateful to the palate. According as each individual variety has, during the time of development, received its just mete of necessaries in food, light, and heat, so will the ultimate combination of elements be, and from such proportions will the chemical action be guided. If there has been any undue disturbing cause during growth by excessive shade, heat, cold, dryness, moisture, or sudden transitions, or from one to the other of any of these, so will it act to a disadvantage, and more particularly will this happen at the time of the last "swell." The uneven balance of these nice points is the main reason why grapes, under artificial culture, so often ripen off a bad color, and remain coarse in texture; the natives rot and fall off prematurely, and many pears become gritty and cracked, from the simple fact of there having been a sudden check to nature's action, the result of which is, the cells do not break up uniformly, the coloring matter is not duly deposited: in the right parts, chemical action is arrested, and the flavor is deficient.

The blistering of the leaves may be traced to the same origin, and there is little doubt but most of the diseases we have to complain of are the effect from the same cause.

We have nothing to gain by all cultivators becoming simply theorists, but this does not argue against the necessity for a more general diffusion of physiological knowledge in practical pomology, and the above few remarks are hastily thrown together with the hope that the subject may be freely discussed in future pages of your valuable, journal, as the merit of the case demands.