ART. XIII.-Circulation in Vegetables; by Prof. E. EMMONS.

THE remarks in the following communication, are offered with some reluctance, as most of them are in opposition to the common opinions of the day. The subject too is one attended with difficulties, and investigations relating to it cannot result in the clearness and certainty which are so desirable in one of so much interest. The opinions advanced in this paper are not newly adopted or taken up recently or, suddenly, but have been deliberately formed and have been often expressed in my lectures on vegetable physiology. I confess however that they have not been formed so much from direct experiment as could be wished; they may therefore have little weight in the estimation of the public. But as the subject is interesting, suggestions of any kind may not be lost, as they may lead others more able than myself into a course of investigation, which, will result in discovering the true course of the circulation in vegetables. Writers on this subject seem to have desired to establish too much by analogy. They have studied the functions of the different organs in animals and those functions they have transferred to vegetables. Thus they make the leaves perform the functions of the lungs, and they discover also in vegetables a double circulation, notwithstanding there is not the vestige of a heart. There are doubtless analogies between the two kingdoms, bnt they are of a more general nature; such for instance as the following. The different orders of animals feed on different kinds of food, and we might infer what we already know, that different plants might require different kinds of soil. As climate has a controlling influence over animals, we might infer the same of vegetables. Different orders of animals are furnished with different kinds of apparatus for the circulation of the blood; so may the different orders of vegetables be thus diverse in the mode of circulating their fluids. Such are the analogies which it is safe to admit. But we may not compare the different parts of vegetables with those of animals and say that their functions are analogous, because the two kingdoms are not formed on the same general plan. I shall now proceed with the subject by noticing, in few words, the theory of Mr. Knight of England, as given in the Phil. Trans. for 1803. His theory may be stated concisely as follows, "water taken up by the roots of vegetables ascends principally through the central wood to the leaves, in which organs some of it

is exhaled; the remaining sap passes into a different sytem of vessels which commence near the surface of the leaves and pass out through the mid rib into the liber. It now receives the name of cambium. In its progress downwards, it adds a new layer to the alburnum and also to the liber. These deposits constitute the annual ring, so conspicuous in the oak and fir. The object of the ascent of sap to the leaves is to effect changes in it, by exposing it to light air and oxygen. The ascending sap is considered analogous to the chyme and the descending to the chyle of animals. Mr. Knight adduces the following experiments in support of his views. 1. When he removed a ring of bark from the limb of a tree, he found the deposits of new matter to be made principally on the upper edge of the ring. He explains the result of the experiment by saying, that the descending sap or cambium could not reach the lower edge of the ring, in consequence of the removal of a portion of continuous matter. Mr. Knight's statement of the result of this experiment is certainly remarkable. He does not say that the deposite is entirely on the upper edge but mostly. From an examination of a great many trees which have been girdled, or which have lost large patches of bark, I am satisfied that there is a deposit at both edges of the ring. He admits that if a leaf is left growing near the lower edge, the thickness of the deposit is augmented. 2. If two parallel rings of bark are removed, leaving between them a leaf, it dies in consequence, it is said, of cutting off the supply of cambium from above. But is not the supply of sap equally cut off from the root; the leaf it is evident, is as much insulated from the supply below as from above. 3. If a branch be stripped of its leaves it dies; "the organs," as Mr. Knight would say "which elaborate the cambium are destroyed." But may it not be said that the power which assists in the elevation of the sap is removed, and that the limb dies of starvation. These are the experiments of Mr. Knight to prove that the cambium descends, and that the office of the leaves is to effect a change in the sap, they acting as media through which the sap is exposed to the light, atmosphere, &c. similar in fact to what takes place in the lungs of animals.

In the farther discussion of the subject it will be my object to show that the descent of the fluids in vegetables is unnecessary and never takes place in ordinary circumstances. I do not undertake to prove that the sap cannot descend at all, but that the sap in a vegetable deriving its nourishment from the roots only ascends, and that it is not a function of the leaf to elaborate the fluids, or to effect those changes

in them, in order that they may be fitted for the nutriment of the vegetable.

1. It is evident that changes must take place in the fluids absorbed by the roots, to fit them for the nutriment of the plant. These changes commence, as soon as they are taken into the vegetable system: the most important change however is effected as they pass upward through the neck of the vegetable. This view of the subject is supported by the fact that the neck is the most important part of the plant. It is a vital part; divide a plant here and it is destroyed. The structure of this part appears different. But what seems to favor, still more, the opinion expressed above, is the change, which the fluids visibly undergo in passing through this part. To be convinced of this the reader may examine the Asclepias Syriaca, or milk weed. Divide the root below the neck, and the fluid which exudes is merely watery, but when the division is made at the neck, that peculiar milky fluid appears. In this case, we must admit that the fluid is changed as it passes upward, or as Mr. Knight supposes in the leaves and then passes down to the neck and there stops. If the latter supposition be true, would not accumulations of sap take place in this part. But this is not the case. 2. No power has been pointed out which can cause a descent of the sap in the uninjured vegetable, while the roots remain in the earth. It appears to me that it is unphilosophical to maintain that gravity is a principal cause of the descent of the cambium, as Mr. Knight has stated in the following passages in the Phil. Trans. for 1803. "These causes, (that is of the descent of the sap,) appear to be gravitation, motion communicated by the winds or other agents, capillary attraction, and probably something in the conformation of the vessels themselves which renders them capable of carrying the fluids in one direction rather than another. pp. 277-8. Again, when a tree is deprived of all motion by being trained to a wall, or when a large tree has been deprived of its branches, it becomes unhealthy and not unfrequently perishes, apparently from a stagnation of the descending fluids under the rigid cincture of the lifeless external bark. p. 282. Another cause of the descent of the sap to the root, I have supposed to be capillary attraction and something in the conformation of the vessels themselves; I however consider gravitation as the most extensive and active cause of motion of the descending fluids of trees. p. 283." But if gravitation be the active cause, &c., how can the vegetable overcome this power so as to raise the fluids at all? As

it regards CAPILLARY ATTRACTION, motion by winds, &c. 1 forbear to remark on them as causes of the descent of the sap. Of gravitation I would say, that we ought not assign it as an efficient cause of action or motion, where vitality exists. 3. The growth of stems can be effected where no leaves are developed. The vine of the potatoe growing in the dark or diffuse light of a cellar is almost destitute of leaves. It is a strong case to show that they are not required for assimilation. In all cases, the elongation of the branch and growth of the leaf take place simultaneously. 4. The evaporation of a large portion of the watery part of the sap so far inspissates it, that the descent becomes difficult. Gardeners know that watering delicate plants with barn yard water clogs the vessels and they die if the practice be long continued. If it be diluted with pure water, the practice is highly beneficial, showing us that the water is not poisonous. The phenomena of vegetable nutrition and assimilation may be explained without bringing in the agency of the leaves. The spongioles takes up water, more or less loaded with foreign matter, as carbon, coinmon air, ammonia and other alkaline salts. As soon as the fluids come in contact with the vegetable structure they are more or less changed. In their progress upward, especially in herbaceous plants, they are still more changed and while passing through the neck. When the sap has arrived at the extreme branches, its assimilation is complete and a part of it is employed in effecting the extension of the branches or expansion of the leaves; the remainder is exhaled. That the fluids are changed, in their upward progress, before they have reached the leaves is shown by the fact, that the sap of the sugar maple is sweeter in the higher parts of the trunk than in the roots. Its specific gravity is also greater, and it is to be remembered that the maple is yet leafless. The elongation of the branches is finished in about three or four weeks, and the leafing is perfected in the same time. These two processes engross all the fluids and bring into action all the energies of the plant. Afterwards the sap is differently employed, viz. in forming the annual layer and in developing the buds. I have been led to consider the leaves as organs of exhalation, and not of assimilation. The power, namely, vegetable irritability, which causes the ascent of sap is a vital property, and like animal irritability often acts periodically. Thus after the long repose of winter, with how much energy do vegetables carry on their functions on the opening of spring. A few weeks only are required to transform a desert waste, into a beautiful garden. It is not improbable that the

leaves may assist in the elevation of the sap. After their expansion, not a particle of sap will flow from the wounded vegetable. They assist in this process by the rapid evaporation from their surface. That they may accomplish the functions assigned them, they seem to be fitted to the various situations in which they grow. In tropical climates they are largely expanded, in cold regions they are narrow, contracted and rigid. The circulation of vegetables is not entirely suspended during the winter. As we may still see the buds gradually enlarging, especially in sheltered places. As the vegetable draws its nutriment from the bosom of the earth, beneath its icebound surface, we find it preserving an elevation of temperature above the circumambient air. I wish to present the above remarks rather as hints, than established conclusions; they are offered for the purpose of calling the attention of philosophers anew to the subject, that something more satisfactory may be taught than we find in the existing systems of vegetable Physiology.

Williams College, Dec. 12, 1833.

ART. XIV.-Notice of a Galvanometer; by Dr. JoHn Locke.

TO THE EDITOR.

Dear Sir.-The galvanometer concerning which, I wrote to you last spring has been changed, again and again, until I have finally constructed an instrument with which I am satisfied. The essential part of it is a wire wound around a flat ring of boxwood. The outside diameter of this ring is 3.75 inches, and the inside diameter three. inches. Its thickness is one fourth of an inch. The outside edges wheel, in order to

of it are cut or notched like the teeth of a clock cause it to hold the spiral wire which is coiled around it in a single layer, the several parallel turns as close as possible without being in contact; except at the diameter of the ring, where an opening of the tenth of an inch is left for the introduction of a magnetized needle within the coil. This flat coil is put into the bottom of a cylindrical mahogany box turned in the shape of a snuff box, four and a half inches in diameter and one and a half deep, outside dimensions; the projecting ends of the wire being passed through, near the bottom of it. Immediately above this coil is the card or divided circle, which is attached to a thin wooden ring. The needle is suspended by a silk filament. It is made of a simple