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Show 326 MODIFIED CIRCUl\INUTATION. CHAP. VII. Fig. 1\18 . I : (;" tf..'r'(1 "'· .'fdo. Ox(llis acetosella: circumnutation and nyctitropic movement!> of a nearly full-grown leaf, with filament attached to the midrib of one of the leatlets; traced on vertical glass during 20 h. 45 m. rlown in this and all other cases. By 6.45 A.M. on tho following morning it had risen considerably, and continued to rise for the next hour; but, judging from other observations, it would suon have begun to fall again. Between 11 A.M. and 5.30 PJr, tho leaflet moved at least four times up and four times down b fore the great nocturnal fall commenced; it reached its ltighc.-t point at noon. Similar observations were made on two other 1 aflets, with nearly the same r esults. Sachs and Pfeffer l1ave aiFJo described briefly* tho autonomous movements of tho leaves of this plant. On another occasion the rctiole of a leaf was secured to a little stick close beneath tho I afiets, and a filament ti 1 p cl with a bead of sealingwax was affixed to the mid· rib of one of them, and a mark was placed close behind. At 7 P.M., when tbe leafio(,s were asleep, the filament depended vertically down, nncl the movements of the bead were then traced till 10.40 P.M., as shown in the following diagram (Fig. 129)· "\Vo here Ree that the leaflet moved a little from side to side, as well as a little up and down, whilst asleep. • Sachs in 'Floro.,' 1RG3, p. '170, &c.; Pfeffer, 'Die Period. Bewegungeu,' &c., 1875, p. 53. CHAP. VII. SLEEP OF LEAVES. 327 Oxalis Valdiviana.-The leaves resemble those of the last species, and the movements of two leaflets (the main petioles of both having been secured) were traced during two days; but the tracings are not given, as they resembled that of 0. acetosella, with the exception that the up and down oscillations were not so frequent during the day, and there was more lateral movement, so that broader ellipses were described. The leaves awoke early in the mornFig. 129. Oxnlis acetosella: circumnutntion of leaflet when asleep ; traced on vertical glass during 3 h. 40 m. ing, for by 6.45 A.M. on June 12th and 13th they had not only risen to theit· full height, but had already begun to fall, that is, they were circumnutating. 'Ve have seen in the last chapter that the cotyledons, instead of sinking, rise up vertically at night. Oxalis Ortegesii.-The large leaves of this plant sleep like those of the previous species. Tho main petioles are long, and that of a young leaf rose 20° between noon and 10 P.M., whilst the petiole_ of an older leaf rose only 13°. Owing to this rising of the petioles, and the vertical sinking of the large leaflets, the leaves become crowded together at night, and the whole plant then exposes a much smal'er surface to radiation than during the day. Oxalis Plumierii.-In this species the three leaflets do not sur~oun~ the summit of the petiole, but the terminal leaflet P.roJects m the line of the petiole, with a lateral leaflet on each Bide. They all sleep by bending vertically downwards, but do not ~ecome at all folded. The petiole is rather long, and, one havmg been secured to a stick, the movement of the terminal ~eaflet was traced during 45 h. on a vertical glass. It moved 1~ .a very simple manner, sinking rapidly after 5 P.M., and ?smg ~apidly early next morning. During the middle of the day ~t moved slowly and a little laterally. Consequently the ascendIn~ and descending lines did not coincide, and a single great e~Ipse was formed each day. There was no other evidence of ctrcumnutation, and this fact is of interest, as we shall hereafter see. Oxalis sensitiva.-The leaflets as in the last species bend vert' 11 d ' ' 1 lea Y own at night, without becoming folded. The much e onga,ted main petiole rises considerably in the evening, but in |