Nature.

Manawatu Standard, Volume IV, Issue 270, 11 October 1884, Page 5 (Supplement)

Nature.

The Sensitive Plant.

The singular phenomenon exhibited by this well-knowri, exotic has long been the ail- ' miration of the curious, a puzzle to the botanist, and a standing marvel m the vegetable kingdom. The plant has the property of contracting certain parts of its structure when touched, and is not only sensible to the application^ force, but appears to be influenced by the. surrounding elements. Sudden degrees of heat or cold, steam from -boiling water, .sulphur-fumes, the, odor of Volatile liquids; m fact anything' that affects the nerves of animals, appears also to effect Jh^§e.n3jtive plant. -„ It is- m ih_e highest degree a nervous subject, and, like that species of the. genus Itomo, is m tb.ia country; a thorough hothouse habitant. The subject of our present consideration was originally introduced, from Brazil, and,, along with, other varieties possessing the. same faculty m different degrees,' is common to other parts of South America. The stem of the plant is ; cylindrical, and of a green or purplish color, ; with -two spines at the base of each leaf, besides a few others . scattered, about the branches'. The leaves are pinnatifld, or divided into pairs, supported oh long foqtotalks, and each pinnule is furnished with fifteen or twenty pairs of oblong, narrow, and shining leaflets. From the base, of the leafstalks proceed the peduncles or flower-stalks, each of which supports a bunch of very small white or flesh-colored flowers. The seedvessels are united m packets of twelve or fifteen each, and are edged with minute spines, each 1 husk containing three little seeds. ■ Dr. Hook, Dufay, Duhamel, and other naturalists, have studied this plant with equal attention, and from their observations we learn that it is difficult to touch a leaf of , a .heal thy mimosa — under which name the sensitive plant is also known— even m the most delicate manner without causing it to close. The great nerve which passes along the centre of the leaf serves as a hinge for the sides, to. close upon, and this they ;do with great exactness, the two sides exactly opposing each other. If the pressure is made with considerable force, the opposite leaf of the same pair will be affected at the same time and moved m the same manner. Upon squeezing the leaf still harder, all the leaflets 6ri 'the same side cloae immediately, as if resenting the affront. The effect may be even carried so far that the leaf-stalk will bend to the branch from- which it issues, and the whole plant collect itself as it were into a bundle. „ As boon! as evening approaches, the senaitiv&'planti begins ; to lower its -leaves, till at length they rest upon the stem. With the morning light,, they gradually, re-open. When the leaves have even faded and turned yellow, the plant still continues this action, andre--1 tainS its sensibility when agitated by external influences. A fine rain will not disturb the mimosa at all ; but should the rain fall heavily, and be accompanied by wind, the ■plant -becomes immediately affeetedi ' When irritated and made to close by force, the time necessary i or the leaves to recover their usual position varies from ten to twenty minutes, according' to the season and the hour of the day. Though heat and cold contribute greatly towards its, alternate motion, yet the plant is more sluggish' m its motives arid less sensitive m winter than m summer. After a btaricH .Hals' been separated from the/shrub, fhe,4eaves still retain their sensibility, . and • wflF shut 'on being touched. If the etid'of the detached branch is kept m water, the leaves /.will continue to act for some time. 1 ; '. If , the sensitive plant be plunged into cold water, the leaves will close, but will afterwards re- open ; and if touched m this state, will again shut themselves, as if m the open air, but not so /quickly. This experiment does not seem to injure the plant. If the extremity of a leaf exposed to the rays of the sun is burned with a lens or a match, it closes instantly;; and at the same moment, not only the leaflet which is opposite to it follows its example, but all that are upon the same.stalk. If a drop of sulphuric acid is plactd upon a leaf so as to remain stationary, the plant is not immediately affected ; but when it begins' to spread, the irritation is communicated from one. leaflet to another, till/the whole of' them on the affected stalk are oiosed.~ Although a branch of this wonderful, plant be .cut through three : fourtbs of ik^tliameter, yet the leaves belonging to it retain the same degree of sensibility, and open and shut with their usual freedom. The vapor of boiling water affects ' the' leaves m -the: same manner as if they were burned, and for several hours they appear benumbed, m fact, seldom recovering during the remainder of the day. \ These are some of the principal phenomena connected with this very singular plant.* No doubt, other experiments have been made; but these will serve to show how much akin is the delicate organisation of this plant to that, of the animal kingdom. . Many conjectures have been formed and many theories raised to account satisfactorily for the working of this exquisite machine ; but the mainspring is still hidden,, and <has, as'- far as we know, eluded the' search of the naturalist. It has been supposed' by some that the mimosa is endued with a power of perception which actuates all its motions, and is the connecting link between the animal and vegetable kingdoms. But. at least, an equally rational theory is, that .its movements are purely mechanical. . To enter into a discussion as to the relative merits of these and other theories would exvbeed the limits of this article. We can only the plant as one of those natural [wonders whioh add to our admiration; of "mother ' Nature and her products. — Chamber's Journal.