conspicuous a part in the building up of organic bodies. It may, and no doubt is, present in the cellular tissues, for the same purpose that it is present elsewhere-as a counteracting power to the one which causes decomposition, or acetous fermentation. It is urged that the green part of wood, when burnt, exhibits a greater proportion of carbon than either the albumen or woody fibre. This is owing to the abundance of mucilage and gluten which that part contains, and not to the mere colouring matter. The quantity of carbon extracted from the burnt green wood might, with greater propriety, be suspected of having formed the principal part of the organic structure; for if it was so plainly recognized, there was more than enough to unite with the yellow fluid, as a quantity scarcely perceptible would be sufficient for the purpose. In our opinion, the matter which forms the blue tint is yet unknown to us.

A very curious phenomenon has recently come within our own knowledge, which will throw some light on the subject. We discovered that snow which fell on tanner's spent bark, when the ground underneath was not frozen, became immediately tinged with a beautiful green colour. This green snow lay in patches on a tan walk, and on closely investigating this singular circumstance, we observed that those parts alone of the snow were coloured which lay on pieces of bark that were covered with a dingy, yellow dust. In sprinkling dust of this kind on a board, and covering it with a slice of newly fallen snow, the colouring matter of the dust rose slowly through the pores of the snow, and tinged it throughout with a beautiful, bright green colour. Both the snow and the dust were perfectly dry at the time. This phenomenon did not appear when the dust was laid on ice, or on frozen ground, and then covered with

snow.

If carbon alone were the cause of the green colour, or of the change in the yellow sap, then this green tint would remain fixed, as it were, even when the vitality of the plant had ceased. The very character of carbon consists in its preserving its identity; that is, the perceptible part of carbon remains fixed, and it is only in its perceptible state, as a substance, that we can ever know it. But this is not the character of the matter which produces the green tint in leaves, for let the blue tint come from either a mineral or vegetable pigment, for both can furnish it, its evanescent nature is the same. Be it what it may, light and a slight degree of heat seem necessary to its development. And, as regards its formation in snow, the blue tint must exist in the interstices of snow; and we recollect seeing a remark in corroboration of this, "that snow, when presented to certain rays of light, had a bluish cast throughout." A writer, whose name is not now recollected, attributes the

generation of the green tint to the monas or other infusory animalcules; but this is a gratuitous supposition, and, were it correct, we should still be in the dark respecting the nature of the essence which produced the blue tint in the monas. There is no doubt that animalcules exist in the pores of the cuticle of the leaf, as well as in the interstices of snow and ice, but with the aid of excellent glasses we never could discover in them the least approach to the blue tint.

Although that portion of light which remains perceptible in snow, in conjunction with the heat which all bodies contain when above the freezing point, be sufficient to produce a union between the blue tint of the snow and the yellow tint of the bark, yet a great quantity of solar light is necessary to the continuance of the blue principle in the green colour of leaves. A few days of cloudy weather, as has been observed by Professor Eaton and others, will not only prevent any new union of the blue and yellow tints, but will cause the greater part of the blue tint already formed to disappear from the foliage. As soon as the sun breaks out in full splendour, the pale, sickly colour of the leaves becomes a vivid green again. Can it be proved that there is a deficiency of carbon in the atmosphere, either at night or in cloudy weather.

In the autumn, as soon as the atmosphere is deprived of heat, the circulation of plants becomes languid, the fibres contract, the vessels collapse, there is no action in the cellular tissues, the blue tint is decomposed, and disappears from the leaves. Nothing remains but the yellow colour of the sap, which, being detained in the leaf, undergoes all the changes, from the deepest yellow to orange and red-just such changes as the sap itself undergoes, when brought immediately in contact with the air. This change is not only seen in bruised bark, but in the juices of all fruits, most conspicuous in the common bough or green harvest apple. The green tint, however, never leaves the bark of plants, for, as has been observed, there is always a little circulation in plants, even in the coldest winters. Nor does this green tint ever disappear from the leaves of the family of resinous plants; which latter fact is a good hint to chemists in the fixing or setting of colours.

The green tint appears to be only necessary to the surface of the leaves and bark, its use being to mitigate the intensity of the rays of light, which otherwise would too suddenly decompose the fluids contained in the cellular tissues. These fluids are propelled to the surface for the purpose of evaporation, and for undergoing some change. The green tint continues down the back of a living plant until it reaches the point whence the roots emanate; here solar influence ceases- -or rather the action of light ceases. The green colour not only disappears, but

the roots have not their sap tinged with the yellow colouring

matter.

Roots, when exposed to the light for a length of time, have their bark sometimes tinged with green, but it is not in consequence of the absence of colour, as some suppose, that roots descend or gravitate, or that trunks and branches ascend, in virtue of possessing that colour. It might as well be urged, that a parrot extends and elevates its wings in virtue of the green feathers, and that the feet gravitate or cling to the perch in consequence of being deprived of them.

From the radiating points of a plant proceed differently constructed organs-one set performing the office of feet and mouths, and perhaps lungs, and the other acting as arms and lungs, and perhaps mouths likewise. The construction of the cuticle of the leaves is so different from that of the spongelets at the roots, that it will be seen at once that the spongelets are not destined to excite or produce the green colouring matterand they have not this power for the simple reason that the green tint is not essential to the necessities of the roots.

In sickly plants, where there is a want of vigour, the cuticular action is feeble, and the leaves, even with the aid of light and heat, are unable to generate the green colour. If restoratives are not administered-such as shade and moisture-the plant must die. The cuticle of the leaf is as tender and delicate as the retina of the eye, which cannot, any more than the cuticle of the leaf, bear the strong glare and heat of the sun. When the eye is diseased we protect it from the light by a shading of green. The disease in peach trees, throughout the United States, called the yellows, is nothing more than a disease of the cuticle. If there is a want of healthy action in the pores of the leaf, the tree declines in health, and is not able to resist the cold of winter, the leaves put out in the spring, sickly and pale, and the fruit drops off prematurely ripe; such a tree scarcely survives the next winter. We have frequently restored trees in which the yellow had just made its appearance, by removing them to damp, shady places, and we have seen whole orchards of peach trees, thus diseased, recover their green colour, in the course of a wet summer.

The mere length of the body or trunk of a tree, is of no particular advantage to it; on the contrary, tall trees, with long limbs, are very apt to be injured by wind and lightning. It is well known that trees which have no stems or trunks, but with limbs springing immediately from the ground or radiating point, are rich in fruit and foliage.

After bestowing great pains in the investigation, we are of opinion that the ducts, commonly called sap vessels, as soon as they have sufficiently elaborated the sap, which they abstract

from the interstices, deposit this secretive matter to the parts immediately in the area of the same circumference with them selves. There rests no doubt on our minds that the nutritive fluids enter the spongelets, pass up through the interstices, and are absorbed by the ducts exactly as is the case in that part of the circulatory process of animals. Every thing in the economy of the plant proves that the absorbent vessels deposit the elaborated sap in a lateral direction.

1. If all the leaves and leaf buds be stripped from any section or twig of a tree having fruit buds on it, the fruit on that section never grows, although those above and below it grow.

2. If a hole, about two inches square, be cut in the trunk or limb of a tree, the secretive vessels will furnish matter for a renewal of the abstracted part-but the healing process will proceed from the sides of the wound, and not from the top or bottom. The granulations which are seen above and below the wound, on close inspection, will be found to have proceeded from the sides. The hole, when entirely covered with new bark, shows the true manner in which the healing proceeded, for the middle of the closed wound has a cicatrice of an oblong form.

3. If a square or round piece of bark, of about two inches diameter be cut from a tree, and a piece of bark from another part of the tree is made to fit in the hole very exactly, the edges will unite at the sides first. The top and bottom cut will only adhere by a glutinous ligament, which in time will be displaced by granulations proceeding from the side edges. In most experiments, however, when the piece set in is of two inches diameter-the edges of the top cut never unite.

4. If a limb be cut off closely to the trunk or limb of a tree-so closely to the bark as that no ring or swelling is left attached to the trunk or limb--the wound will heal from the side edges first, and from these side edges granulations will be pushed out, which will in time cover the whole of the wounded parts, leaving an oblong cicatrice, with an indentation in the centre.

5. If part of the base of the limb or twig-the ring or swelling from which all limbs and branches grow--be left attached to the trunk, the healing process goes on rapidly; and from the edge of the whole circumference, leaving the cicatrice round, with a round indentation in the centre.

6. If a limb be cut between the joints, the wound never heals. The edges of the bark, where separated, shrivel, and all that part above the swelling or ring, of which we spoke, decays and becomes a naked stump.

Therefore, the trunk, and all the spaces or intervals between the joints or articulations, are mere shafts or supporters; and it matters not whether they be one inch or twenty feet, as it

The

respects the quantity of nutritive matter they convey. sole use of trunks and limbs is to allow of the upward ascent of crude sap, which sap is conducted through the interstices. The spiral, clostral, and other ducts, being the true absorbents and elaborating vessels, the mere length of the trunk or shaft adds nothing to the goodness of the fruit, or beauty to the foliage. But at the same time that the whole tree has to be supported by the nutriment thus raised, yet a certain portion of it is necessary to the enlargement and repair of these trunks and limbs; consequently, the additional sap, which a high trunk raises up, would be necessary to sustain the mere increase of this trunk.

The vessels, and the porous interstices, which surround each joint, are quite sufficient for the purpose of nourishing the different organs which lie in embryo at the base of every limb or twig where the joints are. It is in these annular swellings that a concentration of nutriment exists, the sap being detained rather longer at this spot.

From these incontrovertible facts, we must draw the conclusion that the crude sap rises through the interstices, and not through any of the vessels or elongated ducts, whether spiral or otherwise. That this crude sap rises to the extreme points of the terminal shoots, and those parts, if not wanted for the uses of the plant, disappear from the leaves and bark. The elaborated sap, or cambium, or whatever it may be called, does not rise at all, but is given out, laterally, as the sap rises, by the vertical ducts, to those parts on a level with each section of these ducts. The elaborated sap of each vesicular division never rises with that which is ascending in the capillary pores.

The elaborative or digestive process, in certain stages, is carried on nearly in the same manner as in animals; the different tubular vessels absorb such portions of the fluid mass which is ascending, as is requisite for the economy of the section that lies on a level with these vessels. Instead, therefore, of a continued stroke from the top to the bottom of the plant and then back again, as in the circulation of the blood, the elaborated mass moves only in its own little sphere. In fact, as Dr. Dutrochet has satisfactorily shown, the fluids must necessarily be confined to a small space, as the absorbents are interrupted at short intervals, and being hermetically closed, as it were, there could be no continued flow or circulation of this digested sap.

To corroborate this opinion of the lateral direction of the proper juices, and the limited action of the vessels which absorb it, we have only to examine the bark of large trees. There is an interlacing, at intervals, of some of these absorbent vessels; they are ranged at right angles with those that are placed vertically, and are very distinct in the bark of the cherry tree.