Mr Redgrave, having carefully inspected the working of the process, has written to Professor Gardner as follows: ‘I think it right to state that having carefully inspected your works at the bottom of Rolt Street, Deptford, it appears to me that the process of the manufacture of white-lead there is free from nearly all the objections on the score of exposure of the persons employed to the injurious effects, hitherto deemed to be inseparable from the occupation. The material and the product are alike isolated, there is an absence of dust, and handling or manipulating is unnecessary.’
As the white-lead manufacturers of our country are not only an influential and wealthy body, alive to their own interest, but also most anxious for the welfare of their operatives, they must hail this new process with much interest, and adopt it gladly. The general public will rejoice to be assured that the valuable and useful white-lead is no longer prepared at the cost of life and health to many, especially women, as has hitherto been the case.
THE SENSITIVE PLANT.
The singular phenomenon exhibited by this well-known exotic has long been the admiration of the curious, a puzzle to the botanist, and a standing marvel in 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 of force, but appears to be influenced by the surrounding elements. Sudden degrees of heat or cold, steam from boiling water, sulphur-fumes, the odour of volatile liquids, in fact anything that affects the nerves of animals, appears also to affect the sensitive plant. It is in the highest degree a nervous subject, and, like that species of the genus homo, is in this 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 in different degrees, is common to other parts of South America. The stem of the plant is cylindrical, and of a green or purplish colour, with two spines at the base of each leaf, besides a few others scattered about the branches. The leaves are pinnatifid, or divided into pairs, supported on long footstalks, and each pinnule is furnished with fifteen or twenty pairs of oblong, narrow, and shining leaflets. From the base of the leaf-stalks proceed the peduncles or flower-stalks, each of which supports a bunch of very small white or flesh-coloured flowers. The seed-vessels are united in packets of twelve or fifteen each, and are edged with minute spines, each 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 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 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 in the same manner. Upon squeezing the leaf still harder, all the leaflets on the same side close 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 soon as evening approaches, the sensitive plant 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, and retains 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 affected. When irritated and made to close by force, the time necessary for 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 in its movements and less sensitive in winter than in summer. After a branch has been separated from the shrub, the leaves still retain their sensibility, and will shut on being touched. If the end of the detached branch is kept in water, the leaves will continue to act for some time.
If the sensitive plant be plunged into cold water, the leaves will close, but will afterwards re-open; and if touched in this state, will again shut themselves, as if in 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 placed 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 closed. Although a branch of this wonderful plant be cut through three-fourths of its diameter, yet the leaves belonging to it retain the same degree of sensibility, and open and shut with their usual freedom. The vapour of boiling water affects the leaves in the same manner as if they were 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 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 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.