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of all the rest. Wars, migrations, and crusades, travel, curiosity, and commerce, have all contributed to store Europe with a multitude of foreign productions, and to transplant our own productions into foreign quarters. Almost all the culinary plants of England, and the greater number of our species of corn, have reached us from Italy or the East*; America has since added some; and it is possible that Australia may yet add many more.
The utmost period of time to which seeds may hereby be kept, and be enabled to retain their vital principle, and, consequently, their power of germination, has not been accurately determined, but we have proofs enough to show that the duration may be very long. Thus, M. Triewald relates that a paper of melon-seeds, found in 1762, in a cabinet of Lord Mortimer, and apparently collected in 1660, were then sown, and produced flowers and excellent fruit; and Mr. R. Gale gives an instance of a like effect from similar seeds after having been kept thirty-three years.
M. Saint-Hilaire sowed various seeds belonging to the collection of Bernard de Jussieu, forty-five years after the collection had been made. consisted of three hundred and fifty distinct species; of these many, though not the whole, proved productive. In some the cotyledon appeared to have nearly, but not entirely, perished: in which, therefore, though the seeds swelled, and promised fairly at first, they died away gradually. And as it is a well-known fact that melons improve from seeds that have been kept for two or three years, he con
* Willdenow, Principles, &c. § 357. + Phil. Trans. vol. xlii.
+ Id. vol. xliii.
ceives that in this case the cotyledons have been ripened during such period.*
Animal seeds or eggs, when perfectly impregnated, appear capable of preservation as long. Bomare, indeed, affirms, that he himself found three eggs, which, protected from the action of the air, had continued fresh in the wall of a church in which they must have remained for a period of three hundred years.t
The integument which covers seeds, eggs, insects, and worms, seldom consists of more than two distinct layers, and is sometimes only a single one; but in the four classes of red-blooded animals it consists almost uniformly of three layers: first, the true skin, which lies lowermost, is the basis of the whole, and may be regarded as the condensed external surface of the cellular substance, with nerves, blood-vessels, and absorbents interwoven in its texture; secondly, a mucous web (rete mucosum), which gives the different colours to the skin, but which can only be traced as a distinct layer in warm-blooded animals; and, thirdly, the cuticle, which covers the whole, and is furnished in the different classes with peculiar organs for the formation and excretion of a variety of ornamental or defensive materials-as hairs, feathers, wool, and silk.
The CUTIS, or TRUE SKIN, is seldom uniformly thick, even in the same animal: thus, in man, and other mammals, it is much thicker on the back than in the front of the body; but in the different classes
Tilloch's Phil. Mag. vol. xlii. p. 208. article of M. Saint
+ Dictionnaire, art. Oeuf.
or genera of animals it offers us every possible variety. Generally speaking, it is thinnest in birds, excepting in the duck tribe and in birds of prey. Its consistency and elasticity in horses, oxen, sheep, and other cattle, render it an object of high value, and lay a foundation for a variety of our most important trades and manufactures. In many
animals it is so thick and tough, as to be proof against a musket-ball, unless propelled by a high charge of gunpowder. It is sometimes found so in the elk, but usually so in the elephant, which, at the same time, possesses the singularity of being sensible to the sting of flies. The skin of the rhinoceros despises equally the assault of swords, musketballs, and arrows.
I have observed already, that in many animals the skin performs the office of a muscle, though it is seldom that any thing like a fibrous structure can be traced in it. The skin of man offers a few partial instances of this power, as in the forehead and about the neck. In most quadrupeds we trace the power extending over the whole body, and enabling them to throw off at their option insects and other small animals that irritate them. The skin of the horse shudders through every point of it at the sound of a whip, and is said to be generally convulsed on the appearance of a lion or tiger. Birds, and especially the cockatoo and heron tribes, derive hence a. power of moving at pleasure the feathers of the crest, neck, and tail; and the hedgehog, of rolling himself into a ball, and erecting his bristles by way of defence.
The colour of the skin is derived from the RETE MUCOSUM, OF MUCOUS WEB, which, as I have already
remarked, is disposed between the true skin and the cuticle. The name of rete, or web, however, does not properly apply to this substance, for it has no vascularity, and is a mere butter-like material, which, when black, has a near resemblance in colour, as well as consistency, to the grease introduced between the nave of a wheel and its axletree. It is to this we owe the beautiful red or violet that tinges the nose and hind-quarters of some baboons, and the exquisite silver that whitens the belly of the dolphin and other cetaceous fishes. In the toes and tarsal membrane of ravens and turkies it is frequently black; in hares and peacocks, grey; blue in the titmouse; green in the water-hen; yellow in the eagle; orange in the stork; and red in some species of scolopax or woodcock. It gives that intermixture of colours which besprinkles the skin of the frog and salamander; but it is for the gay and glittering scales of fishes, the splendid metallic shells of beetles, and the gaudy eye-spots that bedrop the wings of the butterfly, that nature reserves the utmost force of this wonderful pigment, and sports with it in her happiest caprices.
The different colours, and shades of colours, of the human skin, are attributable to the same material. Most of these, however, are intimately connected with a very full access of solar light and heat; for a deep sun-burnt skin has a near approach to a mulatto.* And hence the darkness or blackness of the complexion has been generally supposed to proceed from the effect produced upon the mucous pigment by the solar rays, and especially
Humboldt, Essai Polit. sur la Nouvelle Espagne, &c.
those of the calorific kind, in consequence of their attracting and detaching the oxygene of the pigment in proportion to the abundance with which it impinges against the animal surface, and in the same proportion setting at liberty the carbone, which is thus converted into a more or less perfect charcoal. As this, however, is a subject which I shall have occasion to revert to in a distinct lecture upon the varieties of the human race*, it is unnecessary to pursue it any farther at present.
It is a most curious circumstance, that the children of negroes are uniformly born white, or nearly so; and that the black pigment which colours them is not fully secreted till several months after birth. It sometimes happens, though rarely, that from a morbid state of the secretory organs, there is no pigment secreted at all, or a white pigment is secerned instead of a black; whence we have white negroes, or persons exhibiting all the common characters of the negro-breed in the form of the head and features of the face, with the anomaly of a white skin. And it sometimes happens, though still more rarely, that from a similar kind of morbid action affecting the secretory organs, the black pigment is secreted in alternate or interrupted divisions; and in this case we have negro children with brindled, marbled, or spotted skins; an instance of which was brought to me by a gentleman about two years ago, who had purchased the child in America, and who, I believe, afterwards exhibited it in this metropolis as a public show.
The CUTICLE is the thinnest of the layers that
*Vol. II. Ser. 11. Lect. III.