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Show 378 MODIFIED OIROUMNUTATION. CHAP. VII. stick, and the movements of two leaves were traced on a vertical glass during 72 h. The plants wore still kept in the dark, excepting that at each observation, which lasted 3 or 4 minutes, \ \ y Jt.•:w a.m Mimflsa pudicl"l: circumnutation and nyctit.ropic movement of a lcaflc~ (with pinna secured), traced on a vertical glass, from 8 A.M. Sept. 141 to 9 A.M. 16th, they were illuminated by two candles. On the third day _the leaflets still exhibited a vestige of sensitiveness when formbly pressed, but in the evening they showed no signs of sleep. Nevertheless, their petioles continued to circumnutate distinctly, CHAP. VII. SLEEP OF LEAVES. 379 although the proper order of their movements in relation to tho day and night was wholly lost. Thus, one leaf descended during the first two nights (i.e. between 10 P.M. and 7 A.M. next morning) instead of ascending, and on the third night it moved chiefly in a lateral direction. The second loaf behaved in an equally abnormal manner, moving laterally during tho first night, descending greatly during the second, and ascending to an unusual height during the third night. With plants kept at a high temperature and exposed to the light, the most mpid circumnutating movement of the apex of a leaf which was observed, amounted to 1rao of an inch in one second; and this would have equalled .g. of an inch in a minute, had not the leaf occasionally stood still. The actual distance travelled by the apex (as ascertained by a measure placed close to the leaf) was on one occasion nearly i of an inch in a vertical direction in 15 m. ; and on another occasion .g. of an inch in 60 m.; but there was also some lateral movement. Mimosa albida.*-The leaves of this plant, one of which is hero figured (Fig.l59) reduced to -}of tho natural size, present some Fig. 159. ~ /,;;::; ~~:~\ P~~ / \ Mimosa albidu: leaf seen from vertically above. interesting peculiarities. It consists of a long petiole bearinCY only t · b th .wo pmnm (here represented as rather more divergent an Is usual), each with two pairs of leaflets. But the inner u • Mr. ~histleton Dyer informs stbatthis Peruvian plant (wllich ~dsr:dnt to us from Kew) is con- 81 e by Mr. Bentham ('Trans. Linn. Soc.,' vol. xxx. p. 390) to be ''the species or variety which most commonly represents the .~..11. sensitiva of our gardens.'' |
