greatest distance from the sun, causes that luminary to ascend higher in the heavens, and to be longer above the horizon, and thus produces longer and warmer days. It is a wellknown physical fact, formerly noticed, that the more perpendicularly the sun's rays fall upon the surface of the earth, the greater is the heat they excite. Hence, as the sun, in his northward progress in the ecliptic, daily ascends higher above the horizon, and consequently darts his rays upon our hemisphere in a more perpendicular direction, the temperature of the earth and air gradually increases, and milder and more genial weather ensues. The effect upon the economy of vegetables is more or less rapid, according to their different structures; but in no long period the increased and increasing heat produces a universal developement of foliage and flowers. The earth opens, as it were, her bosom to the sun; all her veins feel the genial influence; and a vital energy moves and works in all her blossoms, buds, and leaves. What was lately barrenness becomes fertility; from desolation and death start up life and varied beauty, as if beneath the reviving footsteps of a present Deity. Hence result all the beautiful and amazing phenomena of spring.

As it is a general property of heat to expand all bodies, so the fibrous and cellular substance, of which vegetables are mainly composed, is now subjected to a gradual expansion; and hence the sap ascends from the roots through the innumerable minute tubes and cells in the trunks and branches, and circulates through the finest veins of the leaves and flowers. There is a curious species of attraction, in virtue of which the sap of plants, and liquids in general, ascend through tubular substances, in seeming contradiction to the law of gravity. It is called capillary attraction, that is, the attraction of hairs, from the hairlike smallness of the tubes in which its effects are greatest and most visible. Its very remarkable phenomena are not yet satisfactorily accounted for; nor have its laws been fully investigated. It has been clearly ascertained, however, that the ascent of liquids is high in proportion to the fineness of the tubes through which they rise. Now, as the tubes of plants are perhaps the

finest that exist, the effects of capillary attraction are more striking in trees than in any other substances; for in them the liquid juices frequently ascend to a height of more than a hundred feet, and circulate to the extremities of their largest branches and leaves.

It may be difficult to say how much of this process is merely mechanical, and how much depends on that mysterious property, the living principle; but there can be no doubt that heat, by promoting the ascent of the sap in plants, is the great external agent in vegetation. It increases in intensity gradually; and its excessive accumulation is frequently checked by atmospheric changes. Herein is the highest designing wisdom. remark yesterday incidentally made, were a summer To recur to a temperature immediately to succeed the cold of winter, many of our plants would be greatly injured, if not totally destroyed. Their delicate vessels and cells would burst by a too sudden expansion, and the bud, prematurely thrust forth into the light and heat of day, would wither and fall off, or remain an abortive excrescence on its paWe should also be deprived of the beauty and interest attached to the gradual developement of leaf and flower, were the great annual transition in the table world effected instantaneously.

rent stem.

vege

In the average winter temperature of our climate, most of our shrubs and trees cannot put forth their leaves. But as, in the advancing season, the temperature increases, one plant after another, according to the sensibility of its buds, and other peculiarities of its structure, sends forth its tender shoots and leaves, in beautiful succession, till every field, and garden, and grove, is teeming with vegetable beauty and perfume. When once a plant has begun to put forth its foliage, and its vegetation has received a momentum, as it were, from the action of the solar heat, it will bear a temperature considerably below its vegetating point, without being much injured or wholly checked in its growth, provided that temperature be not of too long continuance. Here, again, is beneficent arrangement; for, were it otherwise with plants, we should frequently see the beauty of the forest and the field blasted,by a single night's frost.

To

There is a striking analogy between the vegetative effects of the daily increasing temperature of this season, and the wellknown influence of climate upon the geographical distribution of plants. From the first dawn of spring, before the chillness of winter has left the air, to the commencement or middle of autumn, when the year is beginning to wane, flower succeeds flower, and tree after tree comes into leaf, in regular succession. So, also, from the polar circle to the equator, race after race of vegetable forms appears, ascending from the lichens. of Lapland to the spice trees of the tropics. In our gardens, as the temperature of the atmosphere rises, come successively the snowdrop, the crocus, the auricula, the polyanthus, and, in their season, the rest of the splendid train of flowers. In the forest, the willow and the hazel bud earliest in the year; then follow the larch, the beech, the plane, the oak, and the ash; and soon all the silvan scenery is one verdant mass of leaves. These pleasant successions have their parallels in each hemisphere. take the northern, in which we dwell, we find in the remote Arctic coasts of Europe and America, only mosses, lichens, ferns, and a few diminutive creeping plants and shrubs. As we advance southward, appear the various species of firs and pines, which, again, are closely succeeded by the oak, the elm, the lime, the beech, and other forest trees; and, among fruit trees, by the apple, the pear, the plum, and the cherry. More southward still, flourish the vine and the olive, the lemon, the fig, and the orange, fruit trees of a richer and more delicate description; and, intermingling with these, grow the cypress, the cork, the cedar, and the mulberry. Of cereal plants, wheat extends from the sixtieth degree of latitude to the neighborhood of the tropics. Oats, barley, and rye, endure a greater degree of cold; but none of these are found to arrive at perfection within the tropics, except upon elevations several thousand feet above the level of the sea. Within the torrid zone, maize and rice begin to be cultivated. As we approach the equator, the vegetable productions of the earth increase in richness and luxuriance. In the tropical regions, we

meet with the finest fruits and aromatics, and all the plants that most administer to the luxury of man. There flourish the sugar-cane, the coffee-tree, the bread-tree, the palm, the date, the cocoa, the cinnamon, the nutmeg, the pepper, the camphor-tree, and numerous other vegetable treasures.

Thus, between the Arctic circle and the equator, we have every variety of vegetation, as in each of the intermediate regions there are, annually, beautiful successions of trees, shrubs, and flowers. And how can we withhold our admiration from the matchless skill of the Creator, when we consider that all the lovely variety of the phenomena of our Spring, and all the benefits accruing to commerce and civilization, from the present varied distribution of plants, are made simply to depend on modifications of the solar heat? Hence, among other joyful recurrences, the sweet return of Spring, and all the delights that intervene between the appearance of the earliest sprout and the full glories of summer vegetation; and hence the marvellous diversity of aspect, assumed by the vegetable world between the equator and the poles. What surprising, and beneficent, and varied effects! The cause, how grand and simple! But need we wonder at this, seeing it is but in accordance with all the operations of the Great Supreme ? J. D.

FIRST WEEK-WEDNESDAY.

THE COLOR AND FIGURE OF BODIES.

THE admirable variety which we have seen to obtain over all Nature, may be said chiefly to consist of diversities in the color, size, and figure of bodies. We have formerly adverted to the enjoyments and advantages that accrue from this variety; and here it may not be improper to dwell a little on the subject of color and figure, the sources of so much utility and beauty. The term color has two distinct significations. It may merely

express that feeling of the mind which accompanies the sensation produced by any colored object in our organs of sight; or it may denote the peculiar quality of that object, in virtue of which it excites in the mind a certain feeling, or perception of color. Color generally expresses, however, a particular quality of bodies; and it is in this popular sense that we would here understand the term.

We cannot open our eyes, and cast an observant glance upon Nature, without being struck with the beautiful and varied phenomena of color. The fields, the

woods, the mountains, the sky, and the ocean, are tinged with a thousand different hues. Whence proceed all those splendid tints that give such variety and beauty to the drapery of Nature? Are they ideal creations of the mind? Do they exist merely in the eye?—or are they truly qualities of matter? To these questions, the answer is, that, instead of being any of these exclusively, they result rather from a series of beautiful adaptations. First, every beam of light, as was discovered by Sir Isaac Newton, consists of seven distinct kinds of rays, all fitted to produce different colors; next, the surfaces of all bodies are so constituted, as to reflect one or other, all or none, of these classes of rays, or sometimes a mixture of several, or different proportions of them all; and, again, the eye is so exquisitely formed, as to be differently affected by the various kinds of reflected rays, and thus to be the faithful organ of the mind in discriminating between them, and thereby giving rise to all the delights of vision. The rays of color, taking them in the order of their refrangibility, and beginning with the most refrangible, are violet, indigo, blue, green, yellow, orange, and red. One body, absorbs all the rays but the green, which it reflects, and is consequently green. Another reflects the red rays, absorbing all the rest, and is red. An entire unrefracted beam is white; and when a body absorbs all the component rays, there is a negation of color, that is, it is black. A body seldom reflects one of the prismatic colors solely and exclusively; but a greater or less portion of another, or even of several, is