Almost all vegetable physiologists, in describing the assimilation and growth of trees and plants, assume that the sap, being imbibed by the roots, and containing mineral and other matters necessary for growth, is first carried by the pores of the plant to the leaves, and there uniting with the carbonic acid gas imbibed by them, is, by the aid of sunlight, decomposed, and thus adapted to the growth of the plant. It is then returned downward by another set of vessels, and is deposited as new layers in the growth of the plant. This theory, like many others in the infancy of investigations, is likely to be modified, and one assumed more in conformity with the simplicity always observable in nature's laws when fully understood. Where is the evidence that sunlight does decompose carbonic acid gas, or release oxygen from its combination with carbon? The fact that carbonic acid gas is imbibed by the leaves, and oxygen given out, may account for the origin of the theory, but now, when chemistry is shedding its light on this branch of science as well as others, it would seem that electricity can, with more plausibility, be considered as the decomposing agent.

Professor Gray, in his Botanical Text-Book, considers "light" as affecting "the chemical decomposition of one or more of the substances in the sap which contains oxygen gas, and the liberation of this oxygen at the ordinary temperature of the air." He then continues: " The chemist can, in certain cases, liberate oxygen gas from its compounds, but only by the aid of powerful reagents, or of a heat equal to red-hot iron." But does not the beautiful art of electrotyping, or gilding by galvanism, separate " oxygen from its compounds" without a degree of " heat equal to red-hot iron?" And who will say that a very small stream of electricity from a galvanic battery, may not effect the same object, only requiring longer time? Nature effects by imperceptible degrees what man can only accomplish with more rapidity in less time, and on a smaller scale.

In the Farmers' Guide, published in numbers, and commenced in .1850 by Leonard, Scott & Co., and edited by Henry Stephens and John P. Norton, is an essay on "Electro-Culture" that serves to explain the theory under consideration. In this essay, William Sturgeon, of Manchester, who had successfully applied this principle to cultivation, and has shown the relation which exists betwixt the electricity of the air and the earth, says that "this active element of nature is so universally diffused throughout 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," and considers that " trees, shrubs, plants, flowers, and crops of every kind, partake of this electrical distribution, and that each individual object is possessed of more or less of this extraordinary element. A disturbance of the electric fluid, in any body, may be accomplished either by abstraction, addition, or by merely forcing a part of it to some particular side of the body operated on.

"In the first condition, the body would be electro-negative, in the second, electro- • positive, in the third, electro-polar. Any individual object or body may be positive to another, whilst it is negative to a third. Hence the absolute electric state that any body can appear in is in the polar - a condition growing plants must necessarily assame. 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. Hence the particles constituting each and every variety of soil, are endowed with a peculiar electric force - a circumstance of immense importance in the contemplation of the vegetable physiologist.

"The metals are the best electrical conductors, but there are many other kinds of matter which rank high in this capacity; such are trees when full of sap-water, and consequently all growing plants by virtue of the water they contain. Moist land is also a conductor of electricity. Dry sand is a bad conductor; so is dry mould of every kind; but limestone rock and dry chalk are still worse; and dry air is a worse conductor than any of the rest, though moist air is a tolerably good conductor.

"Another grand law of electricity is, that the transmission is uniformly from the positive to the negative parts. Now, as this is a universal law when electric fluid is transmitted from one body or object to another, it follows that the electropositive state of the air, contiguous to growing plants, causes the latter to become electro-polar, even when they are in the act of transmitting fluid to the ground, their upper parts being negative, relative to the roots, whilst the latter, in their turn, are positive to the contiguous manure and soil, to which they deliver up the fluid, or, rather, such portions of them as are not retained for the expansion and growth of the plants.

"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 electrochemical 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 electro-positive 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. This remarkable fact, based as it is on the strict principles of electric action, not only establishes a correct view of the modus operandi by which plants are, enabled to acquire food through the instrumentality of their foliage, but appears to be well calculated to give a clue to every operation by which vegetables become nourished, and elaborate their food, in all the variety of structure they so beautifully assume.

"Contemplations on electro-chemical forces, thus disencumbered of complexity, lead by easy gradations to many recondite operations of nature, and to the discovery of those hidden actions by which the ever-varying transformations of matters are accomplished. They are well calculated to afford a clue to those atomic operations which, in silent reclusion, select the appropriate materials, convey them to their destination, and elaborate them in the structure of every vegetable tissue that is found within and upon the land".

Here, then, this theory, for its simplicity and adaptation, challenges our consent - no roundabout way of attaining an end; for if the former were the true one, and all matters necessary for growth, had to be conveyed to the leaves to be organized or fitted for assimilation, we might reasonably suppose that the deposition of woody matter would be greatest near the leaves soon after it was prepared. But we know the reverse of this is the fact, and very wisely has it been so decreed.

The larger increase in bulk near the roots enables the tree to withstand the accumulated force of the winds, in consequence of an increase of its top.

One circumstance may be noted that has been brought forward as a strong argument for the downward flow of sap, and that is the fact that amateur cultiva-tors sometimes practise what is called ringing a branch to induce fruitfulness - that is, cutting a ring of bark out of a limb, say a quarter of an inch wide, or more, during summer. The effect is, that while the growth of leaves and smaller branches is retarded, that part immediately above the incision will increase faster than the part just below. And if we admit that the sap rises to the leaves through the sap-wood, and descends beneath the bark, carrying with it matter ready prepared for growth, the fact might be accounted for on the principle supposed. But, by admitting electricity as the decomposing agent, the fact can be as readily accounted for. The carbonic acid gas imbibed by the roots and by the leaves, if decomposed by electricity passing either upward or downward, would deposit its carbon nearest to the place of entrance - that is, that what was received by the roots would form wood nearest the roots, and that nearest the leaves would form the wood of the upper branches.

Hence the carbonic acid gas, in descending from the leaves through the sap-water (the largest part of which lies immediately beneath the bark), and meeting with an obstruction by the incision and removing a portion of the bark, would accumulate and be decomposed there, thus adding a larger portion of organizable matter to a less vigorous circulation, thereby inducing greater fruitfulness; for it is a well-known fact among orchardists, that a rapid growth in wood is opposed to fruit bearing, and vice versa.

The writer, having long felt an objection against the theory of the downward flow of sap, as never having seen any facts in support of that view, was gratified in reading the article on "Electro Culture," as the explanations on assimilation and growth of vegetables in that article appeared more reasonable, and more in accordance with known facts, and was entirely free from the difficulties of the old theory. Claiming the right of every individual, however humble, to give his views on any subject of inquiry, and wishing to see candid investigation promoted, this essay is submitted to the readers of the Horticulturist.