Pagina-afbeeldingen
PDF
ePub

or four of these species as worthy of a particular notice, either by some singular mechanism, or by some peculiar provision, or by both.

I. In Dr. Darwin's Botanic Garden (1. 395, note,) is the following account of the vallisneriu, as it has been observed in the river Rhone.—[Pl. XXXV. fig. 1, 2, 3.] “Thev have roots at the bottom of the Rhone. The towers of the female plant float on the surface of the water, and are furnished with an elastic, spiral stalk, which extends or contracts as the water rises or falls; this rise or fall, from the torrents which flow into the river, often amounting to many feet in a few hours. The flowers of the male plant are produced under water; and as soon as the fecundating farina is mature, they separate themselves from the plant, rise to the surface, and are wafted by the air, or borne by the currents, to the female flowers.' Our attention in this narrative will be directed to two particulars; first to the mechanism, the "elastic spiral stalk," which lengthens or contracts itself according as the water rises or falls; secondly, to the provision which is made for bringing the male flower, which is produced under water, to the female flower which floats upon the surface.

II. My second example I take from Withering. (Arrang. vol. ii. p. 209. ed. 3.) “The cuscuta Europæa is a parasitical plant. (Plate XXXVI.] The seed opens and puts forth a little spiral body, which does not seek the earth to take root, but climbs in a spiral direction, from right to left, ap other plants, from which, by means of vessels, it draws its nourishment.” The little spiral body” proceeding from the seed, is to be compared with the fibres which seeds send out in ordinary cases: and the comparison ought to regard both the form of the threads and the direction. They are straight; this is spiral. They shoot downwards; this points upwards. In the rule, and in the exception, we equally perceive design.

III. A better known parasitical plant is the evergreen shrub, called the mistletoe. What we have to remark in it, is a singular instance of compensation. No art has yet made these plants take root in the earth. Here therefore 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, if they be rubbed upon the smooth bark of almost any tree, they will stick to it. And then what follows? Roots springing from these seeds, insinuate their fibers into the woody substance of the tree; and the event is, that a mistletoe

plant is produced next winter;* of no other plant do the roots refuse to shoot in the ground; of no other plant do the seeds possess this adhesive, generative quality, when applied to the bark of trees.

IV. Another instance of the compensatory system is in the autumnal crocus, or meadow saffron, (colchicuin autumnnale.) [Pl. XXXVII.] I have pitied this poor plant a thousand times. Its blossom rises out of the ground in the most forlorn condition possible; without a sheath, a fence, a calyx, or even a leaf to protect it; and that, not in the spring, not to be visited by summer suns, but under all the disadvantages of the declining year. When we come, however, to look more closely into the structure of this plant, we find that, instead of its being neglected, nature has gone out of her course to provide for its security, and to make up to it 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 lies buried ten or twelve inches under ground within the bulbous root. The tube of the flower, which is seldom more than a few tenths of an inch long, in this plant extends down to the root. The stiles in all cases reach the seed-vessel; but it is in this, by an elongation unknown to any other plant.

All these singularities contribute to one end. As this plant blossoms late in the year, and probably would not have time to ripen its seeds before the access of winter, which 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 usual effects of frost."| That is to say, in the autumn nothing is done above ground but the business of impregnation; which is an affair between the anthere and the stigmata, and is probably soon over. The maturation of the impregnated seed, which in other plants proceeds within a capsule, exposed together with the rest of the flower to the open air, is here carried on,

and during the whole winter, within the heart, as we may say, of the earth, that is “out of the reach of the usual effects of

But then a new difficulty presents itself. Seeds, though perfected, are known not to vegetate at this depth in the earth. Our seeds, therefore, though so safely lodged, would, after all, be lost to the purpose for which all seeds are intended. Lest this should be the case, “a second admirable provision is made to raise them above the surface when they are perfected, and to sow them at a proper dis

* Withering, Bot. Arr. vol. i. p. 203, ed. 2d.
+ Withering's Botanical Arrangement, p. 360.

frost.''

to say

tance;” viz. the germ grows up in the spring, upon a fruit stalk, accompanied with leaves.

The seeds now,

in common with those of other plants, have the benefit of the summer, and are sown upon the surface. The order of vegetation externally is this:- The plant produces its flowers in September; its leaves and fruits in the spring following.

V. I give the account of the dionæa muscipula, [Plate XXXVIII.] an extraordinary American plant, as some late authors have related it: but whether we be yet enough acquainted with the plant, to bring every part of this account to the test of repeated and familiar observation, I am unable

Its leaves are jointed, and furnished with two rows of strong prickles; their surfaces covered with a number of minute glands, which secrete a sweet liquor that allures the approach of flies. When these parts are touched by the legs of flies, the two lobes of the leaf instantly spring up, the rows of prickles lock themselves fast together, and squeeze the unwary animal to death.”* Here, under a new-model, we recognise the ancient plan of nature, viz. the relation of parts and provisions to one another, to a common office, and to the utility of the organized body to which they belong. The attracting sirup, the rows of strong prickles, their position so as to interlock the joints of the leaves; and what is more than the rest, that singular irritability of their surfaces, by which they close at a touch; all bear a contributory part in producing an effect, connected either with the defence, or with the nutrition of the plant.

CHAPTER XXI.

THE ELEMENTS.

When we come to the elements, we take leave of our mechanics; because we come to those things, of the organization of which, if they be organized, we are confessedly ignorant. This ignorance is implied by their name. To say the truth, our investigations are stopped long before we arrive at this point. But then it is for our comfort to find, that a knowledge of the constitution of the elements is not necessary for us. For instance, as Addison has well observed, “ we know water sufficiently, when we

* Smellie's Phil. of Nat. His. vol. i. p. 5.

know how to buil, how to freeze, how to evaporate, how to make it fresh, how to make it run or spout out in what quantity and direction we please, without knowing what water is.” The observation of this excellent writer has more propriety in it now, than it had at the time it was made: for the constitution, and the constituent parts of water, appear in some measure to have been lately discovered; yet it does not, I think, appear, that we can make any better or greater use of water since the discovery, than we did before it.

We can never think of the elements, without reflecting upon the number of distinct uses which are consolidated in the same substance. The air supplies the lungs, supports fire, conveys sound, reflects light, diffuses smells, gives rain, wafts ships, bears up birds. 'E; vdatos ta nurta; water, besides maintaining its own inhabitants, is the universal nourisher of plants, and through them of terrestrial animals; is the basis of their juices and fluids; dilutes their food; quenches their thirst; floats their burdens. Fire warms, dissolves, enlightens; is the great promoter of vegetation and life, if not necessary to the support of both.

We might enlarge, to almost any length we pleased, upon each of these uses; but it appears to me almost sufficient to state them. The few remarks which I judge it necessary to add, are as follow:

* I. Air is essentially different from earth. There appears to be no necessity for an atmosphere's investing our globe; yet it does invest it: and we see how many, how various, and how important are the purposes which it answers to every order of animated, not to say of

organized beings, which are placed upon the terrestrial surface. I think that every one of these uses will be understood upon the first mention of them, except it be that of reflecting light, which may be explained thus:-If I had the pow er of seeing only by means of rays coming directly from the sun, whenever I turned my back upon the luminary, I should find myself in darkness. If I had the power of seeing by reflected light, yet by means only of light reflected from solid masses, these masses would shine, indeed, and glisten, but it would be in the dark. The hemispere, the sky, the world, could only be illuminated, as it is illuminated, by the light of the sun being from all sides, and in every direction, reflected to the eye by particles, as nimerous, as thickly scattered, and as widely diffused, a: aje those of the air.

In the sea,

Another general quality of the atmosphere is the power if evaporating fluids. The adjustment of this quality to var use is seen in its action upon the sea. water and salt are mixed together most intimately; yet the atmosphere raises the water, and leaves the salt. Pure and fresh as drops of rain descend, they are collected from brine. If evaporation be solution, (which seems to be probable,) then the air dissolves the water, and not the salt. Upon whatever it be founded, the distinction is critical; so much so, that when we attempt to imitate the process by art, we must regulate our distillation with great care and nicety, or, together with the water, we get the bitterness, or, at least, the distastefulness, of the marine substance: and, after all, it is owing to this original elective power in the air, that we can effect the separation which we wish, by any art or meāns whatever.

By evaporation, water is carried up into the air; by the converse of evaporation, it falls down upon the earth. And how does it fall? Not by the clouds being all at once reconverted into water, and descending like a sheet; not in rushing down in columns from a spout; but in moderate drops, as from a colander. Our watering-pots are made to imitate showers of rain. Yet, à priori, I should have thought either of the two former methods more likely to have taken place than the last.

By respiration, flame, putrefaction, air is rendered unfit for the support of animal life. By the constant operation of these corrupting principles, the whole atmosphere, if there were no restoring causes, would come at length to be deprived of its necessary degree of purity. Some of these causes seem to have been discovered, and their efficacy ascertained by experiment. And so far as the discovery has proceeded, it opens to us a beautiful and a wonderful economy. Vegetation proves to be one of them. A sprig of mint corked up with a small portion of foul air placed in the light, renders it again capable of supporting life or flame. Here, therefore, is a constant circulation of benefits maintàined between the two great provinces of organized nature. The plant purifies what the animal has poisoned; in return, the contaminated air is more than ordinarily nutritious to the plant. Agitation with water turns out to be another of these restoratives. The foulest air, shaken in a bottle with water for a sufficient length of time, recovers a great degree of its purity. Here then again, allowing for the scale upon which nature works, we see the salutary effects of storins and tempesis. The yesty

s*

« VorigeDoorgaan »