Nature. The Sensitive Plant.

Waikato Times, Volume XXIII, Issue 1902, 13 September 1884, Page 6

Nature. The Sensitive Plant.

Thk singular phenomenon exhibited by T. X well-known exotic has long been the adnr'iation of lha curioua, a puzalp to the botanist, and a etanding marvel in the vegetablo kingdom. Thi j phut has the propeity of contracting catain piu'td o'> its structure vhon touched, and i<* not only rensibJe to th« application of force, but appoAVd to bo influenced by the surrounding elements. Sudden degrees of heat or cold, steatn fiom bciliw^ water, salphur-fuinep, the odor of volatile liquids, in foot anything tbat affects tho nerves of anlinal.3, appears also to otttct the sensitive plant. It* is in the highest aegreo a nervous subject, and, like that species of the genus homo, is in this country a thoiough hothouse habitant. The subject of our present consideration was originally introduced fiora Biazil, r,nd, along with other varieties possessing the same faculty in different degrees, ia common to other parts of South America. The stem of the plant is cylindrical, and of a green or purplish color, with two spines oi the base of each leaf, beside? a few others scattered about the Inanches. The leaves are pinnatiud, or divided into pahs, supported on long fopt!»talk'j, and each pinnule is furnished with fifteen or twenty pairs of oblong, nariow, and shining leaflets. From the base of the leafstalks proceed the peduncles or flower-stalks, nocu of which supports a bunch of very small white or flesh colored flowers. Tlie eeedvrssels arc. united in packets of twelve or fifteen each, and are edged With minute spines, each ]>u [ ik containing three little seeds. Dr. Hook, Dufay, Duhamel, and other natu~alists, h^\e studied this plant with equal attention, and from their observations wo learn that it is difficult to touch a leaf of a healthy mimosa— under which name the sensitive plant is also known — even in the most delicate manner without causing it to close. The great nerve which passes along the contie of the leaf serves as a hinge for the side,-, to close upon, and this they do with gieat exactness, the two sides exactly opposing each other. If the pressure is made with considerable foice, the opposite leaf *o£ the same pair will bo affected at the same time aijci moved in the same manner. Upon squeezing the leaf .still harder, all the leaflets on the same side close immediately, as if reiji'iitirig the affiont. The effect may be even earned .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. Ah soon as evening approaches, the sensitive plant begins to lower its leaves, till at length they rest upon the stem. With the raomiug light, they gradually re-open. "When the loaves n>ive even faded and turned yellow, the plant still continues this action, and retains ita sensibility when agitated by external i lfluences. A fine rain will not disturb the .nil iosa at all ; but should the rain fall heavily, and be accompanied by wind, the plant becomes immediately affected. When uritafced and made to close by force, the time nece^avy for the leaves to recover their usual position varies fiom ten to twen'y minutes, according to the season and the hour of the clo>. Though heat and cold contribute greatly towards iU alternate motion, yet the plant is muie plnggish in its motives and less sensitive id winter than in summer. After a branch has been separated from the shrub, the lea-eg alill retain their sensibility, and will s\ut on being touched. If the end of the detpcl-ed branch is kept in water, the leaves\ will continue to act foi some time. If i>?G sen&itive plant be plunged into cold water, the leave 3 will close, but will afterwards re- open ; and if touched in this state, will again &hut tncmselvet., as if in the open air, but not oo quickly. This experiment does not seem to ininre the plant. If the exnemity cf 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 ■tame stalk. If a drop of sulphuric acid is placed upon a leaf so as to remain stationary, the plant k not immediately affected ; but when it begins to spread, the irritation is communicated from one leaflet to another, hll thf whole of them on the affected stalk arc closed. Although a branch of this wondeiful plant be cut through three-fourths of itb diameter, yet the leaves belonging to it iota in the same degree of sensibility, and open and shut with their usual freedom. The vapor of boiling water affects the Icave3 in the same manner as if they wore burned, and for several hours they appear benumbed, in 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 ita 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 exceed the limits of this article. We can only contemplate the plant as* one of those natural wonders which add to our admiration of mother Nature and her products. — Chamber's Journal.