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Show 890 MODIFIED CIROUMNU'l'ATION. CHAP. VII. the day or between 10° and 20° above tho hori2on, and at night vertically upwards. They therefore rise between 70° and 90° at night. The plant was placed at noon in tho clark in tho hothouse, and on the following day the movements of tho loaves were traced. Between 8.40 and 10 30 A.M. they ro e, and then fell ,greatly till 1.37 P.M. But by 3 P.M. they had again rison a little, and continued to rise during tho rest of tl1o afternoon and night; on the following morning they stood at tho same level as on the previous day. Darkness, therefore, during a day and n half dous not interfere with tho periodicity of their movements. On a warm but stormy ove:i•ting, tho plant whilf.;t being brought into the house, had its leaves violently shaken, and at night not one wont to sleep. On the next morning tho plant was taken back to the hot-house, and again at night tho leaves did not sleep; but on the ensuing night they rose in tho usual manner between 70° · and 80°. This fact is analogous wHh what we have observed with climbing plants, namely, that much agitation checks for a time their power of circumnutation; but the effect in this instance was much more strongly marked and prolonged. Colocasia ar1.tiqurwum (Caladium escttlentwn, Ilort.) (Aroidern). -The leaves of this plant sleep by their blades sinking in tho evening, so as to stand highly inclined, or even quito verti~ally with their tips pointing to tho ground.. They arc not prov1ded with a pulvinus. The blude of one stood at noon 1° beneath the horizon; at 4.20 P.M., :wo; at 6 P.M., 43° ; at 7.20 P.M., 69° ;. and at 8.30 P.M., 68°; so it had now begun to rise ; at 10.15I'.M. It stood at 65°, and on the following early morning at 11° beneath t.be horizon. The circumnntation of another young leaf (with Jts Petiole only 3t inches and tho blade 4 incl1es in length), wns traced on a vertical gla' ss during 48 b.; it was cb.m ly 1'1 1 umm. a te~ l through a skylight, and this seemed to distmh tho p1:oper pel'IO· dicity of its movements. Nevertheless, tho lettf icll greatl.y during both afternoons, till either 7.10 PM. or 9 P.M., when Jt rose a little and moved laterally. By an early hour on ~ot~ mornings, it had assumed its diurnal position. The wcll-ma~kle~ lateral movement for a short time in tho early part of tho mg \i was the only interestino- fact which it presented, as this causel the ascending and descbe nding lines not to com· c1•c 1 o , m· acco,r( · ance with the general rule with C·i rcnmnut a t'm g organs · 11 10t movements of the leaves of thi.s plant a1.e th. ~ s o. f tWho mo. 1 avo simple kind· and the tracino- is not worth g1vmg. . ~ 1tl seen that in ' another genus onf the Aroidere, name 1y , Pistia ' 1e CHAP. VII. SLEEP OJ!' LEAVES. 391 leaves rise so much at night that they may almost be said to sleep. Strephium floribundum"' (Graminero).- The oval leaves are provided with a pulvinus, and are extended horizontally or declined a little beneath tho horizon during tho day. Those on the upright culms simply rise up vertically at night, so that their tips are directed towards tho zenith. (Fig. 164.) Fig. 164. Strephium ftoribundum: culms with leaves during the day, and when asleep at night. Figures reduced. Horizontally extended leaves arising from much inclined or almost horizontal culms, move at night so that their tips point towards the apex of the culm, with one lateral margin directed towards the zenith; and in order to assume this position the leaves have to twist on their own axes through an angle of nearly 90°. Thus the surface of the blade always stands vertically, whatever may be the position of the midrib or of the leaf as a whole. The circumnutation of a young leaf (2 · 3 inches in length) was ~during 48 h. (Fig. 165). The movement was remarkably sunple; the leaf descended from before 6.40 A.M. until 2 or 2.50 P.M., and then rose so as to stand vertically at about 6 P.M., descending again late in the night or in the very early morning. th• A. Brongniart first observed of at th~ leaves of this plant and Marsilea sleep: see • Bnll. de la Soc. Bot. de France,' tom. vii. 1860, p. 470. |