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Show :-360 MODIFIED CIRCU.l\INUTATION. Fig. 150. \ '\\'am.U~ I \ \\ I \ \\ a3•~\, I t. \ 8)!.'1. \../ \ '\ Sp:m.f!Jll1; ,, .. .) CHAP. VII. C1HAP. VII. SLEEP OF LEAVES. 361 raised to 120° F., and the sub-petiole straiglltonod itself. Similar experiments with leaves in water were twice l'opeatecl, with nearly tho same result. It sl10nld he aclclocl, that water raisccl to even 122° F. does not soon kill n len.f. A plant was I> laced in darkness at 8.37 A.M., and at 2 P.M. (i.e. after 5 h. 23m.), though the leaflets had sunk considerahly, th •y had by no means acquired their nocturnal vertically cleJ1enclent po. ition. rfcffer, on the other hand, says* that this occmT cl with him in from J h. to 2 h.; perhaps the difference in our results may he cine to the plant on which we experimentcJ being a very young and vigoroml seedling. The Moverneuts of the little Lat£·ml Lcujlets.-These have 1J en so often described, that we will endeavour to be a.· brief as possible in giving a few new facts and conclusions. Tho leaflets ornetimes quickly c'Q.ange their po.-ition hy as much as nearly 180°; and their sub-petioles can then be s en to hecomc greatly curved. They rotate on their own axes, so that their upp r urfaces are directed to all points of the compass. Tho figure described by the apex is an irregular oval or llipse. Th y . ometimcs remain stationary for a period. In the. o several re. pects there is no difference, except in rapidity and ext nt, he two n their movements and the lesser ones perform d by the largo terminal leaflet whilst making it great oRcilln.tion.. Tho movements of the little leaflets are mnch influenced, a.· is well known, by temperature. This was clearly shown by immer.·ing leave with motionless leaflets in cold water, which wa. .-Jowly rai ·eel to 103° F., and the leaflets then moved quickly, des TihinO' about a dozen little irregular circles in 40 m. By this time tho wa.t01· had become much cooler, and tho movements became slower or almost ceased; it was then ra.ised to 100° F., and the leaflets again began to move quickly. On anoth r occasion a tuft of fine leaves was humor ed in water at 53° F., and the lea.:flets were of course motionless. The water was rni ed to 99°, and the leaflets soon began to move; it was mis d to 105°, and tho m~vements became much more mpid; each little circle or oval bemg completed in from 1m. 30 s. to lm. 45 s. There was, however, no jerking, and this fact may perhaps be attribute i to the resistance of the water. Sachs states that the leaflets do not move until tho surrounding air is as high as 71°-72° F., and this agrees with our * ' Die Period. Boweg.,' p. 30. I J |
