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Show 382 MODIFIED CIRCUMNUTATION. CIIAP. m. do not fully apply to the small leaf here figured. The pinnrn move forwards and at the same time sink downwards, whi!. t the main petiole rises considerauly. With respect to the degree of movement: the two terminal pinnm of one specimen formed together an angle of 100° dming the day, and at night of only 38°, so each had moved 31° forwards. The penultimate pinnrn during the day formed together an angle of 180°, that is, they stood in a straight line opposite one another, and at night each had moved 65° forwards. The basal pair of pinnro wore directed Fig. 160. A. B. Acacia Fm·nesimw: A, leaf during the day; B, the 8ame leaf at night. during the day, each about 21° backwards, and at ID.? h t 3 °t forwards so each had moved 59° forwards. But the pwnre 11 the same' time sink greatly, and sometimes bang almost perpe~· dicularly downwards. The main petiole, on the other han ' rises much: by 8.30 P.M. one stood 34°. hig~1er than. ath~~:; and by 6.40 A.M. on the following mormng It was still g by 10° · shortly after this hour the dm. r.n al sm· km' g move- ment co' mmenced. The course of a nearly f u ll -gro wn leaf wtlays traced during 14 h.; it was strongly zigzag, and apparen CHAP. VII. SLEEP Ol!~ LEA YES. 383 represented five ellipses, with their longer axes differently directed. .Albizzia lopltantha (Tribe 23).-The leaflets at night come into contact with one another, and arc directed towards the apex of the pinna. The pinnm approach one another, but remain in the same plane as during the day; and in this respect they differ much from those of the above Schrankia and Acacia. The main petiole rises but little. The first-formed leaf above tho cotyledons bore llleafl.ets on each side, and these slept like those on the subsequently formed leaves; but tho petiole of this first leaf was curved downwards during the day and at night straightened itself, so· that the chord of its arc then stood 16° higher than iu the day-time. ~e;azeuca ericcejolia (Myrtacem ).-According to Bouche (' Bot. Zeit., 1874, p. 359) the leaves sleep at night, in nearly the same manner as those of certain species of Pimelia. fEnothcra mollissima (Onagraricm).-Accorcling to Linnmus {'Somnus Plantarum '), the leaves rise up vertically at night. ~assijlora gracilis (Passifl.oracm).-The young leaves sleep by their blades. hanging vertically downwards, and tho whole length of the petiole then becomes somewhat curved downwards. Externally no trace of a pulvinus can be soon. The petiole of the uppermost leaf on a young shoot stood at 10.45 A.M. at 33° above the horizon; and at 10.30 P.M., when tho blade was vertically dependent, at only 15°, so the petiole had fn.llen 18°. That ofthe next older leaf fell only 7°. From some unknown cause the. leaves do not always sleep properly. The stem of a plant wluch had stood for some time before a north-east window wa~ sec~red to a stick at the base of a youno- loaf the blade of whwh was inclined at 40° below the horizon~ Fr;m its position the lea~ had to be viewed obliquely, consequently the vertically a~~nding and descending movements appeared when traced 0 . Ique .. On the first day (Oct. 12th) the leaf descended in a ~;~~ag line. until late in tho evening; and by 8.15 A.M. on the .had riSen to nearly the same level as on the previous mormng A n t . leafc ·. ew racmg was now begun (Fig. 161). Tho ri ht ontmu~d to rise until 8.50 A.M., then moved a little to the .g ' and afterwards descended. Between 11 A M and 5 p M 1circumnttd .. , .. 't fall u a e ' and after the latter hour the groat nocturnal dott;~menced. At 7.15 P.M. it depended vertically. Tho the fi ne ought to have been prolonged much lower down in gure. By 6.50 A.M. on the following morning (14th) the |
