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Show 374 MODIFIED CIRCUMNUTATION. CUAP. VII. Owing to this movement-to tho leaves being folded-and to tl~o petioles risi~g, the whole plant is .a~ much more compact at mght than ~urmg the day, as .a fast1gmte Lombardy poplar is compared w1th any other spomes of poplar. It is remarkable that when our plants had grown a little older, viz., to a height of 2 or 3 feet, the petioles did not 1·ise at night, and the midribs of the folded leaves were no longer bent back along one side of the petiole. We have noticed in some other genera. that the petioles of very young plants rise much more at night than do those of older plants. 'l'amarindus Indica (Tribe 16).-The leaflets approach or meet each other at night, and are all directed towards the apex of the leaf. They thus become imbricated with their midribs parallel to the petiole. The movement is closely similar to that of Hrematoxylon (see former Fig. 153), but more striking from the greater number of the leaflets. Adenanthera, Prosopis, and Neptunia (Tribe 20).-With Adenanthera pavonia the leaflets turn edgeways and sink at night. In Prosopis they turn upwards. ·with Neptunia olcracect the leaflets on the opposite sides of the same pinna come into contact at night and are directed forwards. The pinnre themselves move downwards, and at the same time backwards or towards the stem of the plant. The main petiole rises. Mimosa pudica (Tribe 20).-This plant has been the subject of innumerable observations; but there are some points in relation to our subject which have not been sufficiently attended to. At night, as is well known, the opposite leaflets come into contact and point towards the apex of the leaf; they thus become neatly imbricated with their upper surfaces protected. The four pinnre also approach each other closely, and the whole leaf is thus rendered very compact. The main petiole sinks downwards during the day till late in the evening, and rises until very early in the morning. Tho stem is continually circumnutating at a rapid rate, though not to a wide extent. Some very young plants, kept in darkness, were observed during two clays, and although subjected to a rather low temperature of 57°-59oF., tho stem of one described four small ellipses in the course of 12 h. We shall immediately see that the main petiole is likewise continually circumnutating, as is each separate pinna ancl each separate leaflet. Therefore, if the movement of the apex of any one leaflet were to be traced, tho course described would be compounded of the movements of four separate parts. CIIAP. VII. SLEEP OF LEA YES. 375 A filament had been fixed on tho previous evening, longitudinally to the main petiole of a nea1·ly full-grown, highlysensitive leaf (four inches in length), the stem having been secured to a stick at its base; and a tracing was made on a vertical glass in the hot-house nnder a high temperature. In the figure given (Fig. 157), the first dot was made at 8.30 A.M. August 2nd, and the last at 7 P.M. on the 3rd. During 12 h. on the first day tho petiole moved thrice down wards and twice upwards. Within the same length of time on the second day, it moved five times downwards and four times upwards. As the ascending and descending lines do not coincide, the petiole manifestly circumnutates; the great evening fall and nocturnal rise being an exaggeration of one of the circumnutations. It should, howe~ er, be observed that the petiole fell much lower down in the evenings than could be seen on the vertical glass or is represented in the diagram. After 7 P.M. on the 3rd (when the last dot in Fig. 157 was made) the pot was carried into a bed-room, and the petiole was fo~~ at 12.50 A.M. (i.e. after ~dnight) standing almost up:~ g~t, and much more highly mclined than it was at 10.40 Fig. 157. P.M. When observed again at J.ll't'mosa .pudi?a: circumnutation and 4A.M. it had begun to fall and n.ycbtropJC move.ment of main pc-continned f IIi . ' twlc, traced dunng 34 h. 30 m. ft . a ng t1ll 6.15 A.M., :b::~ch hour it zigzagged and again circumnutated. Similar S at10ns were made on another petiole, with nearly the ame result. On two other occasions the movement of the main petiolo |
