IN the above enumeration we first notice a unity of purpose under a variety of expedients. Nothing can be more single than the design, more diversified than the means. Pefficles, shells, pulps, pods,.husks, skins, scales armed with thorns, are all mechanically employed for the same end. Secondly we may observe, that in all these, cases the purpose is fulfilled within a just and limited degree. We can perceive that if the seeds of plants were more strongly guarded than they are, their greater security would interfere with other uses, many species of animals would perish if they could not obtain access to them. Here, as in many cases, a balance is to be maintained between opposite Uses. The provision for the preservation of seeds, appears to be directed chiefly against the inconstancy of the elements, and the inclement season. The depredations of animals and the injuries of accidental violence, seem to be provided against by the abundance of the increase.

When nature has perfected her seeds, her next care is to disperse them. The seed cannot fulfill its ends while it remains in the capsule. After the seed ripens, the pericarpium opens to let them out, which is according to rule in each specie's of plant. Some are opened by the action of the frost, some by elastic explosion, throwing the seeds to a distance. Those of most composite flowers are endowed with downy appendages, by which they float in the air, and are carried to great distances. We are compelled to omit to notice the store of nutriment laid up in the seed for the nutriment of the young plant. A striking analogy exists between seeds and eggs of animals; the same point is provided for in the same manner. The white, and that only, is used in the formation of the chicken. The yolk, very little altered or diminished, is wrapped up in the abdomen of the young bird, to serve for its nourishment till it has learned to pick its own food. We give the most common as illustrations because of their being the most forcible.

Our second observation on the mechanical structure of plants, is upon the general property of climbers. In these, plants from each joint issue close to each other, two shoots, one bearing the flower and fruit, and the other drawn out to a tapering spiral tendril, that attaches to anything within its reach, considering that two pur poses are to be provided, for the fruitage of the plant and the sustentation of the stalk. No means could be more mechanical than this arrangement presents to the eye. "We do not see," says a noted author, "so much as one tree, shrub or herb, that hath a stiff, strong, stem, that is able to mount up and stand alone without assistance furnished with these tendrils." We make a single, simple comparison, the pea and the bean, and remark that in the pea they do not make their appearance till the plant has grown to a height to need support.

The hollow stems of canes, straws and grasses; give the greatest possible amount of strength and elasticity for the amount of material used. Joints at stated distances in these tubes are another element of strength without increase of weight, the material being slightly different. With what uniformity and care has nature provided for these stalks of grasses, grains, and canes, by covering each with an impenetrable coat of weather proof varnish.

Grasses seem to be Nature's especial care. With these she carpets her green earth and paints the landscape; with these she feeds the human family, the birds of the air, beasts of the field, and the grub beneath the surface. Cattle feed upon the leaves, birds upon the smaller seeds, many insects upon their roots, and none need be told that corn, wheat, rye, etc., etc., are strictly grasses.

Corn is a monoecious panicious grass, and though the great staple of the west, it seems to be overlooked in its botanical and mechanical construe ture by intelligent growers. Our bread producing plants are grasses. Those families of plants known as grasses, exhibit extraordinary means and powers of increase, hardiness, and an almost unconquerable disposition to spread their faculties for recuperation coincide with the intention of nature concerning them. They thrive under a treatment by which other plants are destroyed. The more their leaves are consumed, the more their roots increase. Many seemingly dry and dead leaves of grasses revive and renew their verdure in spring. In lofty mountains and cold latitudes where the summer heats are not sufficient to ripen their seeds, grasses abound which are able to propagate themselves without seed. The number of the mechanical adjustments are so numerous, we must content ourselves as before remarked with a reference to the'more common and marked instances. Parasitical plants furnish marked illustrations. The Cuseuta Europea is of this class. The seed 'opens and puts forth a little spiral body which docs not seek the earth to take root, but climbs spirally from right to left upon other plants from which it draws its nourishment.

The little spiral body proceeding from the seed is to be compared with the fibres, the seeds send out in ordinary cases. They are straight, this is spiral. They shoot downwards, this shoots upwards. In the rule, and in the exception, we equally perceive the design.

A better known parasitical plant is the mistletoe. We have to remark in it a singular instance of "compensation." No aft hath yet made those plants root in the earth. Here, then, might seem to be a mortal defect in their constitution. Let us examine how this defect is made up to them. The seeds are endued with an adhesive quality so tenacious, that they adhere to the surface or bark of any tree, however smooth. Roots springing from these seeds insinuate their fibres into the woody substance of the tree from which this parasite draws its life and maintenance.

Another marked instance of rare mechanical action is in the Autumnal Crocus (Cholcicum autumnale). How I have sympathized with this poor plant. Its blossom rises out of the ground in the most forlorn condition possible, without a sheath, calyx, or cap to protect it, and that, too, not in the spring to be visited by the summer sun, but under all the disadvantages of declining year. When we come to look more closely at its mechanical organism, we find that, instead of being neglected, nature has gone out of her way to provide for its security, and make up for all its' defects. The seed vessel which, in other plants, is situated within the cup of the flower, or just beneath it, in this plant is buried ten or twelve inches under ground, in a bulbous root. The styles always reach the seed vessel, but in this by an elongation unknown in other plants. All these singularities contribute to one end. As this plant blossoms late in the year, and would not have time to ripen its seeds before the access of winter would destroy them, Providence has contrived its structure such that this important office may be performed at a depth in the earth out of reach of the effects of ordinary frosts. In the autumn nothing is done above the ground but the blooming and fertilization.

The maturation of the impregnated seed, which in other plants proceeds within the capsule exposed with the rest of the flower to the open air, is here carried on during the winter within the earth below the reach of ordinary frost. Here a new difficulty must be overcome. The seeds, though perfected, are known not to vegetate at this depth in the earth. The seeds, therefore, though so safey lodged through the winter, would after all be lost to the purpose to which all seeds are intended. To overcome this difficulty, another admirable provision is made to raise them above the surface, and show them at a proper distance. In the spring the germ grows up upon a fruit-stalk accompanied with canes. The seeds now, in common with those of other plants, have the benefit of summer, and are sown upon the surface.

"How great and marvelous are His works," and how carefully are the minute details of all His creatures, animate and inanimate, provided for. Relation of parts one to another is and must be harmonious in mechanics, so in the animal economy, so in the vegetable world. None of the works of the Deity want these harmonious relations of parts and offices.