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Show 332 l\fODIFIED CillOUl\fNUTATIO~. CuAr. vrr. to avoid errors of ~aralia~, all readings we.re made by looking through a small rmg pamted on the verbcal glass, in a line with the joint of the leaflet and the centre of the graduated arc. In the following diagrams the orrlinates represent tho angles which the leaflet made with the vertical at successive instants.* It follows that a fall in the curve represents an actual dropping of the leaf, and that the zero line represents a vertically dependent position. Fig. 133 represents the nature of the movements which occur in the evening, as soon as the leaflets begin to assume their nocturnal position. At 4.55 PM. tho lelil.et formed an angle of 85° with the vertical, or was only 5° below the horizontal; but in order tha.t tho diagram might get into our page, the leaflet is repro onted falling from 75° instead of 85°. Shortly after 6 P.M. it hung vertically clown, and had attained its nocturnal position. Between 6.10 and 6.35 P.M. it performed a number of minute o. cillations of about 2° each, occupying periods of 4 or 5 m. The complete state of rest of the leaflet which ultimately followed is uot shown in the diagram. It is manifest that each oscillation consists of a gradual I'ise, followed by a sudden fall. Each time the leaflet fell, it approached nearer to the nocturnal position than it did on the previous fall. 'l'he amplitude of the oscillations diminished, while the periods of oscillation becnme shorter. In bright sunshine the leaflets assume a highly inclined dependent position. A leaflet in diffused light was observed rising for 25 m. A blind was then pulled up so that the plant was brightly illuminated (BR in Fig. 134), and within a minute it began to f~tll, and ultimately fell 47°, as shown in the diagmm. This descent was performed by six dcscendin()' steps, precisely similar to those by which the nocturnal fall is effected. The plant was then u.gain shaded (SII), and a long slow rise occurred until another series of falls commenced at BR', when the sun was again admitted. In this experiment cool air was allowed to enter by the windows being opened at the same time. t~1at the blinds were pulled up, so that in spite of the sun shunng on the plant the temperature was not rai~;:ed. . . The effect of an increase of temperature in diffused light 18 I * In all the flio.grHms 1 mm. in the horizontal direction represents one minute of time. EHch mm. in the vertical direction represents one degree of angular move-ment In Fi 17S. 1~~ anrl 134 tho tomp~·mture i~ rcpresenterl (uln~ 1g tlte ordinates) in the seale 01. 1 mm. to each 0 ·1 ° C. 0 111, Fig. 135 each mm. equal~ o·2 ]<. CHAP. VII. SLEEP OF LEA YES. 333 shown in Fig. 135. The temperature began to rise at 11.3.5 A.M. (in consequence of tho fire being Hgllted), but by 12.42 a marked fall had occurred. It may be seen in the diagram that when the temperature was highest there were rapid oscillations Vig. lil4-. Arerrhoa bilirnbi • ao gular . bright illumi.nat' t movement!! ot leaHet during a chan"e from nearly the seme. Ion o shade; temperature (broken line) r;'maiuiug of small arnplit d time nearer th u e, the mean position of the leaflet being at tho the oscillationa\:~rtical. When the tompcmture began to fall, of the leaf a . arne slower and larger, and the mean position lation was s gai~.approached the hot'izontal. The rate of osciJdi~~ gram, T~~: tmes quicker than is represented in the above . ' when the temperature was between 3P and |