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Show 34! MODIFIED CIRC 1\Ir UTATlO"N. CrrAP. Vlf. nnd 11llnfrons, though observed ont of doors and in the greenhonRo, did not chango tho position of their leaves sufficiently at night to be said to sleep. From observations made on two Rleeping ::;pecie::;, it appearB that, as with 1'ropceolum majus, the leaves must be well illuminated during tho day in order to Rleep at night. For . ovoro.l plants, kept all day in a sitting-room with north-cast windows, did not sleep at night; but when the pots were placed on tbe following day out of doors, and were hrought in at night, they slept in tho mmal manner. The trial wa::; repeated on tho following day 11nd night with the same result. Some obsorv11tions were made on tho circumnutation of the le~tves of];, 1ntnus and a1·lM·ens. It will ::;uffice to say that the leaflets of the latter exhibited a double o cillation in tho eour e of ~4 h.; for they fell from tho early morning until 10 15 A.M.,· then rose and zigzag:O'ed greatly till 4r•.M., after which honr the great nocturnal fall commenced. By 8 A.M. on the following morning tho leaflets had risen to their proper height. We have ::;cen in the fourth chapter, that tho lon.ves of J,upinus spPciosus, which do not sleep, circumnutato to an extraordinary extent, making many ellipses in the cour. o of the day. Cytisus (Tribe 2), Trigonella and Mcdicago (Tribe 3).-0nly Fig. 139. A. R. J!cdicago mat'ina : A, lc:wes during the day; B, ]e;tvcs asleep at night. a few observations wore made on thoRfl three genera. ~he petioles on a young plant, about a foot m. 11 01. g ht' of Cyt. ~·s ·us 30 jragrans rose at night, on one occasion 23° and on anothei ~ · Th~ three leaflets also bend upwardR, and at the same time CHAP. VII. SLEEP OF LEA V 8R. 345 approach each other, so that the ba o of the central leaflet overlaps the bases of the two latcml leaflets. They bend up so much that they press against tho ::;tern; and on looking down on one of these 3 oung plants from vertically above, the lower surfaces of the leaflets are visible; and thus their upper surfaces, in accordance with the general rule, are best protected from radiation. Whilst tho leave on these young plants were thus behaving, those on an old bush in full flower did not sleep at night. Trigonella Oretica reRom bles a Melilotus in its sleep, which will be immediately described. According to M. Royer,* the leaves of Medicago maculata rise up at night, and ''so renvorsent nn peu de maniere a presenter obliquomont au ciol lour face inferieure." A drawing is here given (Fig. 139) of the leaves of M. marina awake and asleep; and this would almost serve for Gytisusfra.qrans in tho same two states. Melilotus (Tribe 3).-The species in this genus sleep in a remarkable manner. The three leafl ts of each leaf twist through an angle of 90°, so that their blades stand vertically at night with one lateral edge presented to the zenith (Fig. 140). We shall best understand the other and more complicated movements, if we imagine our elves always to hold the leaf with the tip of the terminal leaflet pointed to tho north. The leaflets in becoming vertical at night could of cour o twist so that their upper surfaces should face to either side· but the two lateral leaflets always twist so that this surface te,nd. to face the north, but as they move at the same time towards the terminal leaflet, the upper surface of tho one faces about N.N.W., 11nd that of ~he o~ber N.N.E. Tho terminal l aflot behaves differently, for It tWJ.Sts to either side, the upper surface facing sometimes ea. t ~nd some~imes west, but rather more commonly we t than east. rhe termmalleaflet also moves in another aud more remarkable manner, for whilst its blade is twisting and becoming vertical, the whole leaflet bends to one side, and invariably to the side towards which the upper surface is directed· so that if this ~urface faces the west the whole leaflet bends t~ the west until It CO mes m' t o contact with the upper and vertical surfa' ce of ;he ~estern lateral leaflet. Thus the upper . ·urfaco of tho e;unal and of one of tho two lateral leaflets is well protected. he fact of the terminal leaflet twisting indifferently to either • 'Annales des Sc. Nat. Bot.' (5th series), ix. 1868, p. 3G8. |