The motions of a marshy plant discovered some time since, in the province of Carolina, are still more singular. Its round leaves are furnished above, and on the sides, with a multitude of notches that are extremely irritable. When an insect happens to creep upon the superior surface of the leaves, they fold up, and inclose the insect till it dies; the leaves then open of themselves. We may daily observe regular motions in some plants in our gardens. Tulips expand their petals when the weather is fine, and close them again at sun-set, or during rain. Vegetables with pods, such as peas and beans, open their shells when dry, and curl themselves up like shavings of wood. Wild oats, when placed upon a table, will move spontaneously, more especially if warmed in the hand. And the heliotrope, or sunflower, with various other plants, always turns towards the sun. These are incontestable facts, of the certainty of which every person may be easily convinced. From them, some conclude that we ought not to deny sensibility to be an attribute of plants; and certainly the facts which are alleged in favour of such an opinion, give it great appearance of probability. But, on the other hand, plants have no other sign of sensibility; and all that they have is entirely mechanical. We plant a shrub and destroy it, without finding any analogy between it and an animal, that we bring up and kill. We see a plant bud, blossom, and bear seed, insensibly, as the hand of a watch runs round the points of the dial. The most exact anatomy of a plant does not unfold to us any organ which has the least relation to those of animal sensibility. When we oppose these observations to those from which we might infer the sensibility of plants, we remain in uncertainty, and we cannot explain the phenomena related above. Our knowledge upon this subject is very imperfect, and is confined to simple conjecture. We neither attribute sensibility to plants, nor deny it to them, with certainty.
The Sensitive Plant.—This singular plant rises from a slender woody stalk seven or eight feet in height, armed with short recurved thorns; the leaves grow upon long footstalks, which are prickly, each sustaining two pair of wings; from the place where these are inserted, come out small branches, having three or four globular heads of pale purplish flowers coming out from the side, on short peduncles; the principal stalk has many of those heads of flowers on the upper part, for more than a foot in length; this, as also the branches, is terminated by like heads of flowers; the leaves move but slowly when touched, but the footstalks fall, when they are pressed pretty hard. It is a native of Brazil, (M. pudica, humble plant,) having the roots composed of many hairy fibres, which mat slowly together; from these come out several woody stalks, declining towards the ground, unless supported; they are armed with short recurved spines, having winged or pinnate leaves; flowers from the axils, on short peduncles, collected in small globular heads, of a yellow colour.
“Naturalists (says Dr. Darwin) have not explained the immediate cause of the collapsing of the sensitive plant; the leaves meet and close in the night, during the sleep of the plant, or when exposed to much cold in the day-time, in the same manner as when they are affected by external violence, folding their upper surfaces together, and in part over each other like scales or tiles, so as to expose as little of the upper surface as may be to the air, but do not, indeed, collapse quite so far; for when touched in the night during their sleep, they fall still further, especially when touched on the footstalks between the stems and the leaflets, which seem to be their most sensitive or irritable part. Now, as their situation after being exposed to external violence resembles their sleep, but with a greater degree of collapsion, may it not be owing to a numbness or paralysis consequent to too violent irritation, like the pantings of animals from pain or fatigue? A sensitive plant being kept in a dark room till some hours after day-break, its leaves and leaf-stalks were collapsed as in its most profound sleep, and on exposing it to the light, above twenty minutes passed before the plant was thoroughly awake, and had quite expanded itself. During this night the upper surfaces of the leaves were oppressed; this would seem to shew that the office of this surface of the leaf was to expose the fluids of the plant to the light, as well as to the air.” Dr. Darwin has thus characterized these plants.—
Weak with nice sense the chaste Mimosa stands,
From each rude touch withdraws her timid hands
Oft as light clouds o’erpass the summer glade,
Alarm’d, she trembles at the moving shade;
And feels alive through all her tender form,
The whisper’d murmurs of the gathering storm;
Shuts her sweet eyelids to approaching night,
And hails with freshen’d charms the rising light.
CHAP. XXXIV.
CURIOSITIES RESPECTING VEGETABLES.—(Continued.)
The Cocoa-Nut Tree—The Bread-Fruit Tree—The Bannian Tree—Fountain Trees—The Tallow Tree—The Paper Tree—The Calabash Tree—Remarkable Oak—Dimensions, &c. of some of the largest Trees now growing in England—Upas, or Poison Tree.
| Admiration, feeding at the eye, And still unsated, dwells upon the theme. Cowper. |