When philosophers began to make observations on the operations of nature, and to form theories respecting its laws, they did so by observing but a few of the facts bearing upon the subject Thus their theories were often very imperfect at first, and founded more upon fancy than fact.. But as facts began to be more and more observed, and finally acknowledged as the only true base of theory, most of these, being fanciful, have been so modified, as to conform nearer to what appears to be the true laws of nature. Witness the ancient theories of the motions of the earth and the planets, Ac., of the circulation of the blood, and the process of - nutrition and growth of animals, as well as the process of nutrition and growth of vegetables. Philosophers have given so much attention and research to the motion of the heavenly bodies, and made themselves so well acquainted with the laws governing the same, as to be able to predict the time and place of the appearance of a hitherto undiscovered planet. The theory of the circulation of the blood, and of nutrition, is believed to correspond very nearly to the laws of its government, and will account for the varied phenomena we witness.

The science of vegetable physiology, being of later origin, may be said to have not yet reached that degree of perfection of which it is capable, nor so fully to correspond to the facts bearing upon it.

When philosophy began to turn its attention to the circulation of the sap, and the growth of vegetable matter, and to form a theory of its laws, the circulation of the blood in the animal economy, and its Jaws of nutrition, were supposed to present a parallel case so nearly, allied, as to be taken as the type of the law in that case. The fact of the circulation of the sap from the roots to the leaves, and the proof that carbonic acid gas was imbibed by them, while water and oxygen gas was given off, seemed to point strongly to the conclusion that the leaves acted to-the vegetable in a similar manner to what the lungs did in the animal. It was believed that the carbonic acid and other substances were taken up by the roots in a fluid or gaseous state with the sap, and then carried by it to the leaves, where, being exposed to sunlight in their broad surfaces, a decomposition or change took place, making these materials organizable, or ready to be assimilated by the plant. This newly prepared matter was now supposed, to descend between the bark and the wood,, and to be deposited as growth, thus carrying out the parallel between the animal and vegetable economy. This parallel is beginning to be seen not to exist to the extent it was once thought.

Professor Gray, in his Botanical Text-Book, says "there is no circulation in plants similar to that in animals".

In the last number of the last v61ume of the Horticullurist (page 555), is an article on the "True Theory of Grafts." In this article, Dr. Lindley's " own words" are directly applicable to the case. "It is, however, now certain," he says, " that although wood is formed by a descending process, yet that Us descent is not in an organized state. Fluid matter - out of which it is produced - passes indeed from above downwards, but the formation itself is wholly local and superficial, and, consequently, there is no such thing as an incasement of the lower part of a tree by wood descending from above."This "important fact," as he terms it, receives " a new demonstration" from the experiment of " Dr. Maclean," who, in grafting a white beet on a red beet, "and vice versa," showed that there was no "blending of the two colors," but that the growth of the white part made white growth, and of the red part made red growth, whether the.root from which it received its sap was red or white. Thus proving, that of each part "its own cells produced its own coloring matter as they formed superficially." "This is entirely consistent," says the writer of the article alluded to, " with all that has been discovered by the modern physiologists who have applied themselves to a study of the natue of the individual cells of which plants consist".

Admitting these positions to be true, and "that each cell has its own inherent power of secretion," and that "fluid matter out of which wood is produced," is " not in an organized state" in its supposed downward descent, it may be asked, where is the necessity for such " descending process" at all? What advantage is gained by the "fluid matter" being carried to the leaves, as is supposed, if, in its descent, it is not organized, but that " each cell has its own inherent power of secretion," and "perseveringly retains that which is natural to it?" Indeed, there are strong reasons for believing that there is no such downward process at all. Where is its evidence? where is the necessity for its existence? It has been supposed that light acts by decomposing the carbonic acid gas in the sap as it is carried through the leaves, and thus enables the plant to appropriate the carbon in building up its own structure. Bnt is there any evidence in- chemistry that sunlight can decompose carbonic acid, or release oxygen from its compounds in any case. Until this is shown, it would seem to be hardly proper to attribute to it an effect without some proof of its power to produce such an effect.

That such an effect is produced, is no evidence that that was the agent in producing it; more particularly, as there is an agent in nature that is known to produce such an effect, and one within reach of every plant.

That agent is electricity, the power of which is perhaps not yet fully ascertained, but enough is already known to consider it fully capable of performing all that may be required of it in the growth of plants. The beautiful art of gilding by galvanism is proof of this. In. this case, the metal is dissolved in acid, the oxygen here dissolving the metal, making it fluid and colorless. Now, if the object to be gilded is connected with the pole of a battery, and galvanism applied, the one pole will attract the oxygen, and the metal in solution will be drawn to the other pole, and will be distributed over the surface to be gilded. Now, as carbonic acid gas is a union of carbon and oxygen (and it is from this that vegetable physiologists generally consider wood is derived in its growth), and as carbon is positive and oxygen is negative, it is fair to presume that the application of electricity in such case would release the oxygen and retain the carbon, and unite it to the already formed wood of the plant.

That carbonic acid gas is carried up by the sap as well as imbibed by the leaves, is now generally admitted, and as this gas is readily imbibed by water, and will unite with it in large proportion, we have the exact condition necessary to effect the object desired, on the application of electricity, without retorting to any supposed hypothesis.

That electricity is present, in sufficient quantities, during the growing season, we have reason to believe from experiments already made. In a work published in New York, and styled "The Farmer's Guide to Scientific and Practical Agriculture," by Henry Stevens, of Edinburgh, and J. P. Norton, of Yale College, is an article on " Electro-Culture." In this article, the author quotes the language of William Sturgeon, of Manchester, who has bestowed much attention to the subject of electricity in all its bearings, and who asserts that "this active element of nature is so universally diffused through every part of the terrestrial creation, that it becomes an occupant Of every part of the earth's surface, and of the shell of air that surrounds it; that trees, shrubs, plants, flowers, and crops of every kind, partake of this electric distribution;" and then goes on to show that "each individual object is requisitely susceptible of disturbance when the circumstances vary," when they become "positive" and " negative" to each other. This condition, "the various objects which, constitute the vegetable clothing of the land are now in precisely the same condition, being positive and negative with regard to each other.

A similar inequality of electric force occurs among growing plants and their manures, and even amongst the various elements which constitute the latter, no two of them being precisely alike at the same time." And after describing the manner of electric action, the writer concludes: "From this train of reasoning, we are led to some of the most interesting points in vegetable physiology. The electro-polar condition of plants qualifies them in an eminent degree for the performance of those operations which develop electro-chemical phenomena; and, what is very remarkable, the laws of this beautiful branch of electricity are rigidly enforced, and admirably complied with, in the decomposition of carbonic acid gas by their foliaceous, parts; for, in this process, the electropositive carbon is drawn to the electro-negative poles of the plants in precisely the same manner as any electro-negative pole, artificially made, would release the carbon from the oxygen, and select it in preference".

Here, then, we have a theory of nutrition and growth of vegetable matter, in connection with the living principle, that will account for all we see of growth, without having recourse to the doubtful theory of the downward flow of sap, and the decomposing power of sunlight. Admit that the sap carries up with it, from the roots, matter suitable for growth, and that with the carbonic acid gas imbibed by the leaves, and distributed through the sap (as it no doubt is), then, by the agency of electricity passing through the sap, and decomposing the gas, the carbon is precisely in the place where needed for growth, .and its conditions, as far as we know them, are as completely fulfilled in that case as they can be supposed to be in the other. It will set aside the necessity of a supposed downward flow of sap, which has been often asserted, but never proved. It will further release the theory of the absurdity of supposing two sets of vessels, one for the upward, and the other for the downward flow of sap, when no such distinction can be perceived, and when there is no power that we know of can produce such an effect Physiologists will doubtless see cause to advance this further step in theory, and no longer assign to nature's laws a round-about way of producing a result, when all we see in her laws are remarkable for simplicity.