« VorigeDoorgaan »
methods, by which one and the same purpose is attain. ed. In the article of breathing, for example, which was to be provided for in some way or other, besides the ordinary varieties of lungs, gills, and breathingholes (for insects in general respire, not by the mouth, but through holes in the sides), the nymphæ of gnats have an apparatus to raise their backs to the top of the water, and so take breath. The hydrocanthari do the like by thrusting their tails out of the water*. The maggot of the eruca labra has a long tail, one part sheathed within another (but which it can draw out at pleasure), with a starry tuft at the end, by which tuft, when expanded upon the surface, the insect both supports itself in the water, and draws in the air which is necessary. In the article of natural clothing, we have the skins of animals, invested with scales, hair, feathers, mucus, froth; or itself turned into a shell or crust: in the no less necessary article of offence and defence, we have teeth, talons, beaks, horns, stings, prickles, with the most singular expedient for the same purpose) the power of giving the electric shock, and, as is credibly related of some animals, of driving away their pursuers by an intolerable foetor, or of blackening the water through which they are pursued. The consideration of these appearances might induce us to believe, that variety itself, distinct from every other reason, was a motive in the mind of the Creator, or with the agents of his will.
To this great variety in organised life, the Deity has given, or perhaps there arises out of it, a corresponding variety of animal appetites. For the final cause of this, we have not far to seek. Did all animals covet the same element, retreat, or food, it is evident how much
* Derham, p. 7.
fewer could be supplied and accommodated, than what at present live conveniently together, and find a plentiful subsistence. What one nature rejects, another delights in. Food which is nauseous to one tribe of animals, becomes, by that very property which makes it nauseous, an alluring dainty to another tribe. Care rion is a treat to dogs, ravens, vultures, fish. The exhalations of corrupted substances, attract flies by crowds. Maggots revel in putrefaction,
I think a designed and studied mechanism to be, in general, more evident in animals than in plants : and it is unnecessary to dwell upon a weaker argument, where a stronger is at hand. There are, however, a few observations upon the vegetable kingdom, which lie so directly in our way, that it would be improper to pass by them without notice.
The one great intention of nature in the structure of plants seems to be the perfecting of the seed ; and, what is part of the same intention, the preserving of it until it be perfected. This intention shows itself, in the first place, by the care which appears to be taken, to protect and ripen, by every advantage which can be given to them of situation in the plant, those parts which most immediately contribute to fructification, viz. the-antheræ, the stamina, and the stigmata. These parts are usually lodged in the centre, the recesses, or the labyrinths of the flower; during their tender and immature state, are shut up in the stalk, or sheltered in the bud; as soon as they have acquired firmness of texture sufficient to bear exposure, and are ready to
perform the important office which is assigned to them, they are disclosed to the light and air, by the bursting of the stem, or the expansion of the petals; after which they have, in many cases, by the very form of the flower during its blow, the light and warmth reflected upon them from the concave side of the cup. What is called also the sleep of plants, is the leaves or petals disposing themselves in such a manner as to shelter the young stems, buds, or fruit. They turn up, or they fall down, according as this purpose renders either change of position requisite. In the growth of corn, whenever the plant begins to shoot, the two upper leaves of the stalk join together, embrace the ear, and protect it till the pulp has acquired a certain degree of consistency. In some water-plants, the flowering and fecundation are carried on within the stem, which afterwards opens to let loose the impregnated seed*. The pea or papilionaceous tribe, enclose the parts of fructification within a beautiful folding of the internal blossom, sometimes called, from its shape, the boat or keel ; itself also protected under a penthouse formed by the external petals. This structure is very artificial; and, what adds to the value of it, though it may diminish the curiosity, very general. It has also this farther advantage (and it is an advantage strictly mechanical), that all the blossoms turn their backs to the wind, whenever the gale blows strong enough to endanger the delicate parts, upon which the seed depends. I have observed this a hundred times in a field of peas in blossom. It is an aptitude which results from the figure of the flower, and, as we have said, is strictly mechanical ; as much so, as the turning of a weather-board or tin cap upon the top of a chimney.
* Philos. Transact. part ii. 1796, p. 502.
Of the poppy, and of many similar species of flowers, the head, while it is growing, hangs down, a rigid curvature in the upper part of the stem giving to it that position; and in that position it is impenetrable by rain or moisture. When the head has acquired its size, and is ready to open, the stalk erects itself, for the purpose, as it should seem, of presenting the flower, and with the flower, the instruments of fructification, to the genial influence of the sun's rays. This always struck me as a curious property; and specifically, as well as originally, provided for in the constitution of the plant: for, if the stem be only bent by the weight of the head, how comes it to straighten itself when the head is the heaviest? These instances show the attention of nature to this principal object, the safety and maturation of the parts upon which the seed depends.
In trees, especially in those which are natives of colder climates, this point is taken up earlier. Many of these trees (observe in particular the ash and the horse-chesnut) produce the embryos of the leaves and flowers in one year, and bring them to perfection the following. There is a winter therefore to be gotten .over. Now what we are to remark is, how nature has prepared for the trials and severities of that season. These tender embryos are, in the first place, wrapped up with a compactness, which no art can imitate: in which state, they compose what we call the bud. This is not all. The bud itself is enclosed in scales ; which scales are formed from the remains of past leaves, and the rudiments of future ones. Neither is this the whole. In the coldest climates, a third preservative is added, by the bud having a coat of gum or resin, which, being congealed, resists the strongest frosts. On the approach of warm weather, this gum is softened, and ceases to be a hinderance to the expansion
of the leaves and Aowers. All this care is part of that system of provisions which has for its object and consummation, the production and perfecting of the seeds.
The seeds themselves are packed up in a capsule, a vessel composed of coats, which, compared with the rest of the flower, are strong and tough. From this vessel projects a tube, through which tube the farina, or some subtile fecundating efluvium that issues from it, is admitted to the seed. And here also occurs a mechanical variety, accommodated to the different circumstances under which the same purpose is to be accomplished. In flowers which are erect, the pistil is shorter than the stamina; and the pollen, shed from the antheræ into the cup of the flower, is caught, in its de scent, by the head of the pistil, called the stigma. But how is this managed when the flowers hang down (as does the crown-imperial for instance), and in which position, the farina, in its fall, would be carried from the stigma, and not towards it? The relative length of the parts is now inverted. The pistil in these flowers is usually longer, instead of shorter, than the stamina, that its protruding summit may receive the pollen as it drops to the ground. In some cases (as in the nigella,) where the shafts of the pistils or stiles are disproportionably long, they bend down their extremities upon the antheræ, that the necessary approximation may be effected..
But (to pursue this great work in its progress), the impregnation, to which all this machinery relates, being completed, the other parts of the flower fade and drop off, whilst the gravid seed-vessel, on the contrary, proceeds to increase its bulk, always to a great, and in some species in the gourd, for example, and melon), to a surprising comparative size; assuming in different plants an incalculable variety of forms, but all evidently.