This section is from "The Horticulturist, And Journal Of Rural Art And Rural Taste", by P. Barry, A. J. Downing, J. Jay Smith, Peter B. Mead, F. W. Woodward, Henry T. Williams. Also available from Amazon: Horticulturist and Journal of Rural Art and Rural Taste.
M. Leclerc, of Tours, finds in sensitive plants not only a nervous but a muscular system. The muscles are placed in the irritable portions of the plants, and are tuberculous and moniliform in their structure; one set connected with the nutrition, the other with the life of the plant.
Near Gatun, the ground was thickly covered with the sensitive plant, precisely the same species which we cultivate.
The movement of the leaves of the Mimosa pndica have their origin in certain enlargements, situated at the articulation of the leaflets with the petiole, and of the petiole with the stem. Those only which are situated in the last articulation are of sufficient size to be submitted to experiment If, by a longitudinal section, the lower half of this swelling be removed, the petiole will remain depressed, having lost the power of elevating itself; if the superior half be removed, the petiole will remain constantly elevated, having lost the power of depressing itself. These facts prove that the motions of the petiole depend on the alternate turgescence of the upper and . lower half of the enlargement, situated at the point of articulation: and that contractibility is not the principle of these motions. If one part of the plant be irritated, the others will soon sympathize, or bear witness, by the successive falling of their leaves, that they have successively felt the irritation. Thus, if a leaflet be burnt slightly by a lens, the interior movement which is produced will be propagated successively to the other leaflets of the leaf, and thence to the other leaves on the same stalk.
A very clever French experimentalist, Mons. Dutrochet, found, 1st - That this interior movement is transmitted equally well, either ascending or descending. 2d - That it is equally well transmitted, even though a ring of bark has been removed. 3d - That it is transmissible, even though the bark and pith be removed so that nothing remain to communicate between the two parts of the skin except the woody fibres and vessels. 4th - That it is transmissible, even when the two parts communicate merely by a shred of bark. 5th - That it may be transmitted even when the communication exists by the pith only. 6th - But that it is not transmissible, when the communication exists merely by the cortical parenchyma. From these very interesting experiments, it results that the interior movement produced by irritation, is propagated by the ligneous fibres and the vessels. The propagation is more rapid in the petioles than in the body of the stem; in the former it moves through a distance of from three to six-tenths of an inch in a second; in the latter, through from eight to twelve-hundredths of an inch, during the same portion of time. External temperature does not appear to exert any influence on the rapidity of the movement, but very sensibly affects its extent.
Absence from light, during a certain time, completely destroys the irritability of the plant. Such change takes place more rapidly when the temperature is elevated, than when it is low. The return of the sun's influence readily restores the plant to its irritable state. It appears, therefore, that it is by the action of light, that the vital properties of •vegetables are supported, as it is by the action of oxygen that those of animals are preserved, consequently, etiolation is to the former what asphyxia is to the latter.
M. Desfontames has shown that plants, even in their motions accommodate themselves to an alteration in their condition. This naturalist took some sensitive plants with him in a carriage; and observed that as the carriage began to roll, the plants at first trembled and drooped; but soon, accommodating themselves to the jolting, gradually began to raise their heads until the leaves had gained their usual position on the stalks. He repeated the experiment several, times, and always with the same results. If the carriage, after a brief halt went on again, the leaves would droop forthwith, but the danger of being shaken from their petioles was soon removed by the plants re-assuming the erect position, which they then continued to retain.
The shrinking Mimosa is well known to be one of the most sensitive of all curi-osites of the vegetable creation. A mere nothing makes her tremble ; a small cloud hiding the sun disturbs her; the lightest wind makes her uneasy, and quickly she folds herself up. She rolls up her leaves when night comes on, and opens herself again with the first dawn of morning. In the tropics there are vast plains covered with these sensitive plants, which are affected at the slightest circumstance. The gallop of a horse frightens them; the nearest flowers close themselves, and the rest, warned by their sentinels, follow immediately. They hang their heads, most anxiously, when a wanderer approaches them, and should he insult but a single flower by touching it, an electrical movement seems to go over the whole field; they all take alarm, and all feel the attack. They are as susceptible as human beings are to the use of narcotics. A few drops of tincture of opium scattered over them, is sufficient to quiet and make them go to sleep. The botanist, Desfontaine, once placed one of these sensitive plants in his wagon, and it folded itself quickly. However, the wagon went on, and as nothing further was done to the plant, it became quiet in time.
When the wagon, however, at last stopped, and the moving ceased, the plant once more got frightened, and carefully shut itself up.