Mimosa pudica

“ The lower part of the petiole is often swollen (fig. 20, p) , forming the pulvinus, formed of cellular tissue, the cells of which exhibit the phenomenon of irritability. In Mimosa pudica (fig. 20) a sensitiveness is located in the pulvinus which upon irritation induces a depression of the whole bipinnate leaf, a similar property exists in the pulvini at the base of the leaflets which fold upwards. The petiole varies in length, being usually shorter than the lamina, but sometimes much longer. In some palms it is 15 or 20 ft. long, and is so firm as to be used for poles or walking-sticks. ”

“ No mention, however, is made of the observations of Bonnet and of Mairan to the effect that the periodic movements of Mimosa pudica continued when the plant was kept in prolonged darkness.
In Section 2, after describing the structure of a leaf, Hill remarks that "Leaves are always surrounded by the air; and they are occasionally and variously influenced by heat, light, and moisture. They are naturally complicated, and they act on most occasions together. ”

“ Millardet observed a daily periodicity of tension in Mimosa pudica. He found that maximum tension occurs before dawn; the petiole becomes erected, the movement being upwards or towards the tip of the stem. Tension decreases during the day, and reaches a minimum early in the evening; in correspondence with this is the fall of the petiole, the movement being away from the tip of the stem. [C] If the plant were placed upside down the periodic movement of the petiole in relation to the stem will evidently remain the same, but become reversed in space. ”

“ In the case of Oxalis sensitiva two-thirds of the petiole, and in that of Mimosa pudica, apparently the whole of the short sub-petioles of the leaflets have been converted into pulvini. With pulvinated leaves (i.e. those provided with a pulvinus) their periodical movements depend, according to Pfeffer, [23] on the cells of the pulvinus alternately expanding more quickly on one side than on the other; whereas the similar movements of leaves not provided with pulvini, depend on their growth being alternately more rapid on one side than on the other. ”

“ Cesalpino noticed the movements of tendrils and climbing plants, and was surprised to see that the latter to some extent seek for their supports. These were every-day phenomena, but the striking sensitiveness of the leaves of Mimosa pudica introduced from America could not fail to attract attention, and so we find an essay on the causes of it in Robert Hooke's 'Micrographia' of 1667. The irritability of the stamens of Centaurea had been already mentioned by Borelli in 1653. ”

“ Although the cotyledons of Smithia sensitiva rose from a horizontal position in the middle of the day to a vertical one at night, those of S. Pfundii, which are thick and fleshy, did not sleep. When Mimosa pudica and albida have been kept at a sufficiently high temperature during the day, the cotyledons come into close contact at night; otherwise they merely rise up almost vertically. The circumnutation of those of M. pudica has been described. The cotyledons of a Bauhinia from St. Catharina in Brazil stood during the day at an angle of about 50° above the horizon, and at night rose to 77° ”

“ Thus the leaflets of Mimosa pudica acted on by light from above fold upwards, the phototropic effect being positive. But the same leaflets acted on by light from below exhibit a folding upwards, the phototropic effect being now negative. Effects precisely the opposite are found with the leaflets of Biophytum and Averrhoa. They fold downwards whether light acts from [Pg 314] above or below. Finally, a radial organ in found to exhibit under light of increasing intensity or duration, a positive, a dia-phototropic, or a negative phototropic curvature. ”

“ Reptiles are distinguished by torpidity, and the length of time they can live without food. Birds, on the contrary, exhibit ceaseless activity and high muscular power. The ant is as conspicuous for intelligence and size of brain among insects as the quadrumana and man among vertebrata. Among plants the Leguminosæ are distinguished by a tendency to sleep, folding their leaves at the approach of night. In the genus Mimosa, especially the Mimosa pudica, commonly called the sensitive plant, the same tendency is magnified into an extreme irritability, almost resembling voluntary motion. ”

“ The record was taken on a moving plate, the mag­ni­fi­ca­tion employed being two thousand times, and successive dots made at intervals of two seconds. It was a matter of surprise to me to find that the growth of the plant was affected by an intensity of stimulus far below the limit of our own perception. As regards the relative sensitiveness of plant and animal, some of my experiments show that the leaf of Mimosa pudica in a favourable condition responds to an electric stimulus which is one-tenth the minimum intensity that causes perception in a human being. ”

“ Is the plant equally excitable throughout day and night? If not, is there any definite period at which it practically loses its ex­cit­abil­ity? Is there, again, another period at which the plant wakes up, as it were, to a condition of maximum ex­cit­abil­ity?
In the course of my in­ves­ti­ga­tions on the irritability of Mimosa pudica, I became aware of the existence of such a daily periodicity; that is to say, the moto-ex­cit­abil­ity of the pulvinus was found to be markedly diminished or even completely abolished at a certain definite period of the day ”

“ In this particular it very much resembles the P. repens, and, if left at liberty, would no doubt, like that species, creep or spread itself about on the earth. Our figure was made from a plant lately in the conservatory of G. H. Hibbert, esq., but recently consigned to J. Knight, his botanic gardener, who has commenced nurseryman in the King’s Road, Chelsea, with the whole of that well known valuable collection. [Pg 103]
[Pg 104]
PLATE DXLIV. MIMOSA PUDICA.
Bashful Mimosa.
CLASS XXIII. ORDER I.
POLYGAMIA MONŒCIA. Various Dispositions upon one Plant.
ESSENTIAL GENERIC CHARACTER.
Hermaph. ”

“ In the small swamps which surround the town of Mompox on the Magdalena River, we discovered a very beautiful aquatic Mimosa (Desmanthus lacustris) , a representation of which is given in our “Plantes équinoxiales” (t. i. p. 55, pl. 16) . In the chain of the Andes of Caxamarca we found two Alpine Mimosas (Mimosa montana and Acacia revoluta) growing at elevations of from 9000 to nearly 9600 feet above the level of the sea.
As yet no true Mimosa, (in the meaning of the word as established by Willdenow,) nor even any Inga, has been found in the temperate zone. ”

“ 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. ”

“ Mimosa with simple leaves, veiny on both sides, linear, and blunt ended; branches growing close and upright; flower heads grow by pairs, opposite, and at the insertion of the leaf into the stem.
REFERENCE TO THE PLATE.
1. A Floret, (natural size) .
2. The Empalement, (magnified) .
3. The Blossom, (magnified) .
4. One Thread and its Tip, (magnified) .
5. The Pointal, (magnified) .
This species of New Holland Mimosa, has as yet, escaped even the indefatigable, and accurate Dr. Smith; it is from Port Jackson, whence the seeds were transmitted by Colonel Paterson in the year 1793. ”

“ Creeping convolvuli and others have made use of the slender lianas and hanging air roots as ladders to climb by. Now and then appears a Mimosa or other tree having similar fine pinnate foliage, and thick masses of Ingá border the water, from whose branches hang long bean-pods, of different shape and size according to the species, some of them a yard in length. Flowers there are very few. I see, now and then, a gorgeous crimson blossom on long spikes ornamenting the sombre foliage towards the summits of the forest. ”

“ The staircase response in such a tissue is thus explained from considerations that have just been adduced.
The results obtained with Mimosa not only corroborate them, but add incontestable proof of the simultaneous existence of both A and D changes. The physio­logic­al condition of a plant, Mimosa for example, is greatly modified by the favourable or unfavourable condition of the environment. In a hyper-tonic condition its ex­cit­abil­ity becomes very great; in this condition the plant responds to its maximum even under very feeble stimulus. ”

“ Rising high over the palms grew a large tree, with long out-reaching branches. It was the “zamang” tree—a species of mimosa, and one of the most beautiful trees of South America. Its trunk rose full seventy feet without a branch; and then it spread out in every direction in numerous horizontal limbs, that forked and forked again until they became slender boughs. Those branches were clad with the delicate pinnate leaves that characterise the family of the mimosas.
Many of the pupunha palms grew under the shadow of this zamang, but not the tallest ones. ”

“ Mimosa, the common 'sensitive plant' of the tropics, cultivated in conservatories. An impulse set up at the tip of a pinnule of one of these plants is conducted through petioles, stems and branches to a distance of a meter at a rate varying from 6 to 31 mm. per second. A study of the structure of the plant reveals the presence of a connected series of long tube-like cells in the fibro-vascular bundles, usually turgid, and containing relatively small protoplasts. It is argued that impulses take the form of hydrostatic disturbances communicated through the system of tubes. ”

“ Only here and there are found, interspersed among the Gramineæ, a few herbaceous dicotyledonous plants, consisting of two very low-growing species of Mimosa, (Sensitive Plant) , Mimosa [121] intermedia, and Mimosa dormiens, which are great favourites with the wild horses and cattle. The natives give to this group of plants, which close their delicate feathery leaves on being touched, the expressive name of Dormideras—sleepy plants. For many square miles not a tree is seen; but where solitary trees are found, they are, in moist places, the Mauritia Palm ”

“ It is interesting, amongst the other strange wonders, animal and vegetable, that are duly set forth, to come across a plant that must be very familiar to most persons, the sensitive plant, the Mimosa sensitiva of Brazil, though in his description of it our author cannot resist an added touch of the marvellous, imputing to it a power of observation that later writers would hesitate to confirm, for he says—“The herb Viva when roughly touched will close the leaves, and not open them again until the man that had offended it had got out of sight.” ”

“ There may be a difficulty on account of the diurnal movement of Mimosa; the leaf, generally speaking, has a movement in a downward direction from morning till noon, after which there is a comparative state of rest. It is better to choose the time of noon for experiment. In any case the response to stimulus is very abrupt and in strong contrast with the slow diurnal movement. A horizontal pencil of light was thrown upwards by means of a small mirror and made to fall on the lower half of a pulvinus of the Mimosa leaf. ”

“ No part of the creation supposed to be insentient, exhibits to an imaginative observer such an aspect of spiritual life and such an apparent sympathy with other living things as flowers, shrubs and trees. A tree of the genus Mimosa, according to Niebuhr, bends its branches downward as if in hospitable salutation when any one approaches near to it. ”

“ The velocity of trans­mission is very much lower in winter than in summer. In the petiole of Mimosa, the velocity in summer is as high as 30 mm. per second; in winter it is reduced to about 4 mm. The lowering of velocity in winter is partly due to the prevailing low temperature and also to the depressed state of physio­logic­al activity.
EFFECT OF AGE.
In a Mimosa plant, different leaves will be found of different age. Of these the youngest will be at the top. Lower down, we obtain a fully grown young leaf, and near the base, leaves which are very old. ”

“ There is a strict correspondence between the responsive movement of the leaf of Mimosa, and the movement due to growth. An increase or positive variation of turgor induces an erection of positive response of the leaf of Mimosa, and a positive variation or enhancement of the rate of growth. A diminution or negative variation of turgor induces a fall or negative response of the leaf of Mimosa, and a negative variation or retardation of the rate of growth.
External tension within limits, enhances the rate of growth. ”

“ Mimosa elegans is one of the handsomest of the family that yet been introduced from New Holland, and very rare, being at this time in no other private collection in this country, but that of A. B. Lambert, esq. from whom we received our specimens; and in whose conservatory it is now in full flower, his plant being about ten feet high and very much branched, with profusion of flowers. It is hardly possible to express the extreme delicacy of the blossoms. ”

“ Its long roots stretch out horizontally in the ground, and the approaching tread of a horse or man is communicated through them to the plant, and produces this singular phenomenon. When the danger is gone by, and the earth ceases to vibrate, the mimosa may be seen again to raise its head, quivering and trembling, as though not yet fully recovered from its fears. ”