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Show 376 MODIFIED CIRCUMNlJ'I'A'l'ION. CIIAP. VII. was observed every two or three minutes, the plants being kept at a rather high temperature, viz., on the first occasion at 77°-81° F., and the filament then described 2~ ellipses in 69m. On the second occasion, when the temperatme was 81 °-86o F., it made rather more than 3 ellipses in 67 m. Therefore Fig. 157, though now sufficiently complex, would. have been in~ comparably more so, if clots had been made on tho glass every 2 or 3 minutes, instead of every hour or half-hour. Although the main petiole is continually and rapidly describirw small ellipses during the day, yet after the great nocturnal rising movement has commenced, if dots are made every 2 or 3 minutes, as was done for an hour between 9.30 and 10.30 PJr. (temp. 84° F.), and the dots are then joined, an almost absolutely straight line is tho result. To show that the movement of the petiole is in all probability clue to the varying turgescence of the pulvinu., and not to growth (in accordance with the conclusions of Pfeffer), a very old leaf, with some of its leaflets yellowish and hardly at all sensitive, was selected for observation, and tho plant was kept at the highly favourable temp. of 80° F. 'l'he petiole fell from i:1 A.M. till10.15 A.M., it then rose a little in a somewhat zigzag line, often remaining stationary, till 5 P.M., when the great evening fall commenced, which was continued till at least 10 P.M. By 7 A.M. on the following morning it had risen to the same level as on the previous morning, and then descended in a zigzag line. But from 10.30 A.M. till 4.15 P.M. it remained almost motionless, all power of movement being now lost. The petiole, therefore, of this very old leaf~ which must have long ceased growing, moved periodically ; but instead of circumnutating several times during the day, it moved only twice clown and twice up in the course of 24 h., with tho ascending and descending lines not coincident. It has already been stated that the pinnro move independently of the main petiole. The petiole of a leaf was fixed to a c~rk support, close to the point whence the four pinnro diverge, with a short fine filament cemented longitudinally to one of tho two terminal pinnre, and a graduated semicircle was placed close beneath it. By looking vertically down, its angular or lateral movements could be measured with accuracy. Between noon and 4.15 P.M. the pinna changed its position to ono side by only 7°; but not continuously in the same direction, as i~ mo:ed four times to one side , and three times to tho opposrto side, SLEEP OF LEAVES. 377 in one instance to tho extent of 16°. This pinna, therefore, circumnutated. Later in the evening thci four pinnro approach each other, and tho one which was obsm·ved moved inwards 5~0 between noon and 6.45 P.M. Ten observations were made in the course of 2 h. 20m. (at average intervals of 14m.), between 4.25 and 6.45 P.M.; and there was now, when the leaf was going to sleep, no swaying from side to side, but a steady inward movement. Here therefore thm·e is in the evening the same conversion of a circumnutating into a steady movement in one direction, as in tho case of the main petiole. It has also been stated that each separate leaflet circumnotates. A pinna was cemented with shellac on the summit of a little stick driven firmly into tho ground, immediately beneath 11 pair of leaflets, to the midribs of both of which excessively fine glass filaments were attached. This treatment did not injure the leaflets, for they went to sleep in the usual manner, and long retained their sensitiveness. The movements of one ofthem were traced during 49 h., as shown in Fig. 158. On the first day the leaflet sank down till 11.30 A.M., and then rose tilll~te in the evening in a zigzag line, indicating circumnutation. On the second day, when more accustomed to its new state, it oscillated twice up and twice down dm·ino- the ~ h. ;his llant wa~ subjected to a rather low temper:ture, VIz., 62 -64 F.; had1t been kept warmer, no doubt the movements. of the leaflet would havo been much more rapid and complicated. It may be seen in the diagram that the ascending and descending lines do not coincide; but the large amount of late~l movement in the evening is the result of the leaflets bendmg towards the apex of the leaf when going to sleep. ~other ~eaflet was. casuall_Y observed, and found to be conmually ~ucumnutatmg dunng the same length of time. be!he cu.cumnutation of the leaves is not destroyed by their mg SUbJected to moderately long continued darkness· but the prope · di · ' .r perio mty of their movements is lost. Some very young seedlings were kept during two days in the dark (temp. 57°-59° ~.),except when the circumnutation of their stems was occa: IOnally observed; and on the evening of the second clay the :flats did not fully and properly go to sleep. The pot was en placed for three days in a dark cupboard, under nearly the sahme temperature, and at the close of this period the leaflets SOWed • . a to no signs of sleepmg, and were only slightly sensitive to uch. On the following day the stem was cemented to a |