imperfect imitation of that which has come from the hands of the Creator. In the latter, there are many things which art in vain attempts to imitate, the mechanical skill is so exquisite, and the adaptations so nice. And then, with what waste of thought, with what laborious stretch of ingenuity, with what patient toil and pains is the human instrument constructed. Who will venture to compare with this the creative power of the Omnipotent?

SECOND WEEK-TUESDAY.

GROWTH OF VEGETABLES.

I HAVE, in a former volume, given an account of the first developement of vegetable productions, and detailed the general principles of their organization, and of their vital powers.*

What remains, as introductory to a sketch of the properties of individual plants, which arrive at maturity during the summer months, is to explain their mode of growth, and the various contrivances by which they are adapted to the climate and localities in which they are found.

The first thing worthy of observation on this subject, is, that two different modes have been adopted in the growth of vascular plants, with obvious reference to the state of external nature in the latitudes where they are respectively placed; the one of which is named exogenous, [growing from without] the other, endogenous, [growing from within.] In the former, the successive additions to the substance of the stem, are made on the exterior side of the parts from which they proceed; in the latter, this process is reversed, and the growth is the result of additions made internally. All the trees of the regions north of the tropics, belong to the exogenous or

*Spring,' Articles Vegetation, Developement of Seeds and Plants, Vital Powers of Plants, &c. 5

III.

IX.

der; while a large proportion of tropical plants belong to the endogenous.

Of endogenous plants, the palm-tree may be taken as an example. The stem of this tree, in its usual state, is perfectly cylindrical; it attains a great height, and from its summit sprouts a considerable tuft of leaves. It is composed of an extremely dense external layer of wood, while the texture of the interior gradually becomes softer and more porous as it approaches the centre. With re

gard to its essential character, however, it appears to be uniform in every part, having neither medullary rays nor true outward bark, nor any central pith; in all which respects it differs entirely from the ordinary exogenous

trees.

In the first stage of its growth, a circle of leaves is formed, shooting upwards from the neck of the plant, and attaining, during the first year, a certain height. The following year, another circle of leaves arises, which grow from the interior of the former circle, forcing it outwards as their vegetation advances, and as woody matter is deposited within. Thus the growth proceeds, each succeeding year producing a fresh crop of leaves intermixed with ligneous matter; and these, exerting an outward pressure, extend and swell outwards the layers in which they are enclosed, until the latter, acquiring greater density, no longer admit of further distention, and remain permanently fixed. This solidity of texture first takes place in the outermost and oldest layer, the internal layers being consolidated each in its turn. As soon as the outer layer is rendered too hard for yielding to internal pressure, the vegetative force of the inner layers is immediately directed upwards. In this manner, the tree rises by successive yearly stages, the growth always proceeding from the interior; a mode of developement which has been compared to the drawing out of the sliding tubes of a telescope. The whole stem, whatever height it may contain, never increases its diameter after its outward layer has been consolidated. A circle of leaves annually sprouts from the margin of the new layer of wood, leaving, when they fall off, a circular impression

round the stem, by means of which the age of the tree may be ascertained:*

Notice has elsewhere been taken of the complicated structure of exogenous trees,† which are composed of wood, bark, and pith. A few words may be here said of their mode of growth, which differs so entirely from that above detailed. The plant in both cases rises from a germ; but, in the trees now under consideration, the stem gradually swells in thickness as it extends in height, consisting of the first layer of wood, with its central pith and its covering of bark. This is the process of the first year. In the succeeding spring, a fresh impulse is given to vegetation, and a new growth commences from the upper end of the original stem, as if it were the developement of a new bud; and, at the same time, a layer of cellular tissue is formed by the deposition of new materials on the outside of the former wood, and between it and the bark. This is followed by a second layer of wood, enveloping the new layer of cellular tissue. While this process is going on in the wood, corresponding changes take place in the bark, and a new layer is added on its inner surface, which is called the liber. All these additions to the thickness, of course, press against the bark, which, being elastic, yields to the pressure to a certain extent, but at length gives way, forming numerous cracks; and these are filled up by the exudation of the vegetable matter, called cambium, formerly mentioned.

Such is a general statement of the different processes of growth in exogenous and endogenous plants, constituting a very striking difference in the constitution of vegetable substances in different climates. That this difference is the contrivance of Creative Wisdom to adapt vegetation to the diversities of light and heat, and the other constituents of the weather, in various latitudes, cannot reasonably be doubted by any person acquainted with

* [This rule is not without exceptions. The trunk of the Royal Palm, (Oreodoxa regia,) for instance, is perfectly smooth, the circular impressions, or rings, being obliterated till within a short distance of the summit.-AM. ED.]

+ See 'Spring,'-Developement of Seeds and Plants, &c.

the system of Nature; but the processes of vegetation are too obscure, and the effects of the atmosphere under different modifications are too little known, to enable us distinctly to show the final causes of these alterations; and all, perhaps, that can be positively asserted on the subject is, that the one class of plants droops and decays when transferred to the locality of the other, a sufficient proof of a profound and calculated adaptation.

In various other particulars, not elsewhere mentioned, the adaptation can be more easily traced, because it depends on known mechanical laws. Thus, the graceful curve with which the stem of a tree rises from the ground, is the form obviously best calculated to give stability to the trunk. Evidence of express mechanical design is likewise afforded by the manner in which the trunk is subdivided into branches, spreading out in all directions, manifestly for the purpose of affording the leaves a greater extent of surface, and thus enabling them to receive the fullest action of both light and air, so essential to the health of the tree. The branches also are so constructed, as to yield to the irregular impulses of the wind; and again, by their elasticity, to return to their natural positions; and by their alternate inflexions on opposite sides, to promote the motion of the sap, and thus to contribute to the healthy action of the vegetable powers.

If any person is inclined to attribute the circumstances we have mentioned to the accidental combinations of unintelligent agents, the best answer which can be given is to refer him to the thousand other instances of design which appear in every department of Nature. We do not rest the argument on a few insulated facts; but confidently appeal to the whole tendencies of the principles which regulate the material world, and to the innumerable minute particulars which display an intelligent and beneficent Hand. The facts above detailed might have little weight if they stood alone; but they are individual illustrations of a universal system, and in this light are valuable, as adding to the cumulative evidence, which so irresistibly constrains the mind to acknowledge a present Deity.

SECOND WEEK-WEDNESDAY.

HORTICULTURE.-PRINCIPLES ON WHICH IT IS FOUNDED.

In turning to the consideration of vegetable substances, as they exist during the summer months, it is necessary that we should make a very limited selection, for they are so various, and their history and properties are are so interesting, that volumes might easily be written on this subject alone. For this reason, I shall confine myself to plants which man has appropriated to his own use; and shall commence with the varied products of the garden, noticing those only which are the most valuable or the most remarkable.

Gardening is a branch of agriculture at once important and interesting. It depends for its existence on the bountiful provision which the Creator has made for the supply of vegetable substances fit for human nourishment and enjoyment during all the productive seasons of the year, exclusive of the cereal plants, which are only reaped in autumn, and seem more especially destined to furnish food to be stored up for relieving the wants of the unproductive season of winter. The paternal care of the Creator, in the respect I have mentioned, is very conspicuous. The constitution of these different kinds of plants points out their intended uses; and there is at once a grateful variety, and a wise adaptation to the circumstances of man, in such productions, which cannot be sufficiently admired. Had the whole of Nature's bounties been crowded into the autumn months, not only would the unequal distribution of labor, elsewhere mentioned,* have been productive of serious inconveniences, but we should have been deprived of the healthful and agreeable varieties afforded by fresh-culled vegetables, with their succulent properties and pleasant flavor. While corn is in every respect wisely contrived for hoarding, the grain being full

*See Spring,' Article, The Labors of the Husbandman wisely Distributed over the Year.