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Show 358 MODIFIED CIRCUl\1N U'l,ATION. CrJAP. VII. Gircumnutation.- Tho circum1mtating movements of four young shoots were obsorvell durinn- 5 h. 15m.; and in this time each compl ted an oval figure of • mall · ize. Tho main petiole also circumnutates rapidly, for in the course of 31m. (temp, 91 oF.) it changed its courRc hy as much as a rectangle six times, describing a figure which appar ntly represented two ellipses. Fig. 149, A. B. Desmodiwn gyrans: A. stem during ihc t!n)' ; n, stem with leaves a>leep. 'opietl from a photograph ; figures reduced. Tho movement of tl10 terminal leaflet hy moans of its subpetiole or pulvinus is quite as rapid, or oven more so, than that of the main I)Otiole ancl hafi much rrreater amplitude. Pfeffer has seen* these lea' flets move throub gh an angle of ~·I ll ~ course of from 10 to 30 seconds. h · A fine, nearly full-grown leaf on a young plant, 8 inc es 1~ height, with the stem secured to a stick at the base of ~e 21:~1: was observed from 8.30 A.M. Juno 22nu to 8 A.~r. Ju * 'Die PerioJ. Deweg.,' p. 35. CHAP. VII. SLEEP OF LEAVE . 359 In the diagram given on tho next page (Fjg. 150), tho two curved broken lines at the base, which represent the nocturnal courses, ought to be prolonged far downwards. On tho ti1·st day the leaflet moved thrice down and thrice up, and to a considerable distance laterally; tho course was alr-;o remarkably crooked. The dots were generally made every hour; if they had been made every few minutes all the lines woulcl ha,vc been zigzag to an extraordinary degree, with hero and there a loop formed. We may infer that this would have been tho case, because five dots were made in tho course of 31m. (b tween 12.34: and 1.5 P.M.), and we see in the upper part of tho diagram how crooked the conrso hero is; if only tho first and last dots had been joined we should have had a straight line. Exactly the same fact may bo seen in the lines representing the course between 2.24 P.M. and 3 P.M., when six intormccliato dots were made; and a.gain at 4.46 and 4.50. But tho result was widely different after 6 P.M.,-that is, after tho great nocturnal descent had commenced; for though nino dots wore then made in the course of 32m., when those wore joined (·co Figmo) the line thur-; formed was almost straight. The leaflets, therefore, begin to descend in the afternoon by zigzag lines, but as soon as the descent becomes rapid their whole energy is expended in thus moving, and their cour o becomes rectilinear. After the leaflets are completely asleep they move very little or not at all. Had the above plant been subjectc l to a higher temperature than 67°-70° F., the movements of the terminal leaflet would probably have been even more rapid and wider in extent than ~hose shown in the diagram; for a plant was kept for some time 1U the hot-hou8e at from 92°-93° F., and in the course of 35m. theapexofa leaflet twice descondcu and once a. ccndcd, travelling over a space of 1·2 inch in a vertical direction and of ·82 inch in 11 horizontal direction. Whilst thus moving tho leaflet aL·o r~tated on its own axis (and thi wa a point to which no attenhon had been before paid), for the plano of the blade clifi'cr d by flo after an i~terval of only a few minutes. Occasionally the eafiet stood st11l for a shOTt time. Thoro was no jerkin rr movement, which is so characteristic of tho little lateral leafl~ts. A ~udden and considerable fall of temperature causes tho terminal eafiet to sink downwards; thus a cut-off loaf was immersed in ::~rat 95o F., w~ich was slowly raise l to 103° F., and after- . ds allowed to smk to 70° F., ancl the sub-petiole of thl:l tcrnunalleafiet then curved downwards. Tho water was afterwardr-; ,, I |
