OCR Text |
Show 372 MODIFIED CIRCUMNU'rATION. CHAP. VII. therefore their lower surfaces face but little outwards at night. The petioles, which during tho day are inclined only a little above tho horizon, rise at night in a remarkable manner, and stand nearly or quite vertically. This, together with the dopondont position of the leaflets, makes the whole plant wonderfully compact at night. In the two foregoing figures, copied from photographs, the same plant is represented awake and asleep (Fig. 155), and we sec how different is its appearance. Oas.sia mimosuides.-At night the numerous lcanets on each leaf rotate on their axes, and their tips move towttrds the apex of the leaf; they thus become imbricated with their lower surfaces directed upwards, and with their midribs almost parallel to the petiole. Consequently, this species differs from all the others seen by us, with the exception of the following one, in the leaflets not sinking down at night. A petiole, the movement of which was measured, rose 8° at night. Cassia Ba1·clayana.-The leaflets of this Australian species are numerous, very narrow, and almost linear. At night they rise up n little, and also move towards the apex of the leaf. For instance, two opposite leaflets which diverged from one another during tho day at an angle of 104°, diverged at night only 72° ;. so thn,t each had risen 16° above its diurnal position. Tho pot1ole of a young leaf rose at night 34°, and that of an older leaf .l9o. OwinO' to the slio·ht movement of the leaflets and the considerable ~ovement ~f the petiole, the bush presents a different appearance at night to what it docs by clay; yet tho leaves can hardly be said to sleep. . The circumnutating movements of the leaves of 0. flonbunda, calliantha, and f1ube8ce?IS were observed, each during three or four days; they were essentially alike, those of the last-named species being the simplest. Tho petiole of C. jloribunda was secured t~ a stick at the base of the two terminal leaflets, and a filamcn was fixed alonO' the midrib of one of them. Its movements were traced from 1 ~.M. on August 13th to 8.30 A.M. 17th; but those during the last 2 h. are alone given in Fig. 156. From 8 A.M. 0~1 each day (by which hour the leaf had assumed its diurnal positioll) to 2 or 3 P.M., it either zigzagged or circumnutatcd ove~ nearly the same small space.· at between 2 and 3 P.M. tho grcad evening fall commenced. 'l'h' e lines representm· g t h..1 s fa J l an . the eady morning rise are oblique owing to the peculiar manner in which the leaflets sleep as a' lready descr1'b ed · After the , leaflet was asleep at 6 p.M., ' and whilst the glass fil arne nt hun0.,. CHAP. VII. SLEEP 01.<' LEA VBS. perpendicularly down, the movement of its apex was traced until 10.30 P.M.; and during this whole time it swayed from side to side, completing more than one ellipse. Batthinia (Tribe 15).- Fig. 15G The nyctitropic movements of four species were alike, and were highly peculiar. A plant raised from seed sent us from South Brazil by Fritz Muller, was more especially observed. The leaves are large and deeply notched at their ends. At night the two halves rise up and close completely together, like the opposite leaflets of many Legumi-nosm. With very young plants the petioles rise con-siderably at the same time; one, which was inclined at noon 45° above the hori- ;/,A, / y::' ,/ /,., i·/· /~ ) zon, at night stood at 75° ; it thus rose 30° ; another rose 34°. Whilst the two halves of the leaf are ciosin o· the midrib at first sink~ vertically downwards and afterwards bends backwards, so as to pass close along one side of its own upwardly inclined petiole ; the midrib being thus elirected towards the stem or axis of the plant. The anO'le which the midrib forr:ed with the horizon was measured in one case at dif- :ere~t hours: at noon it stood horizontally; late in the even~ g 1~ depended vertically; then rose to the opposite side, and di .15 P.M. stood at only 27° beneath the horizon beinO' rected t ' o owards the stem. It had thus travelled through 153°. |