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Show 336 l\IODIFIED CIRCUl\INU'f.A.TlON. CHAP. VII. same branch, though moving a little in the same direction, also bend downwards; they thus occupy a somewhat different position, relatively to the centre of the earth and to the branch, from that of the petioles on tho upright branches. With respect to the leaflets, they move at night towards tho a pox of the petiole until their midribs st..'l.nd nearly parallel to it; and they then lie neatly imbricated one over the other. Thus half of the upper surface of each leaflet is in clo o contact with half of the lower surface of the one next in advance; and all the leaflets, excepting tho basal ones, have the whole of their upper surfacC>s and half of their lower surfaces well protected. Those on the opposite sides of the same petiole do not come into close contact at night, as occurs with the leaflets of so rmt11y LoguminoFro, but are separated by an open furrow; nor could they exactly coincide, as they stand alternately with respect to one another. The circumnutation of the petiole of a loaf ~ of an inch in length, on an upright branch, was ohservcd during 06 h., and is shown in the preceding diagram (Fig. 136). On the first morning, the leaf fell a little and then rose until 1 ur., and this was probably duo to its being now illuminated through a skylight from above; it then circumnutatecl on a very small scale round the same spot until aLont 4 P.~r., when the great evening fall commenced. During the ln.ttcr part of the night or very early on the next morning tho lcnJ rose again. On the iocond clay it fell during the morning till 1 P.M., and this no doubt is its normal habit. From 1 to 4 P.M. it rose in a zigzag line, and soon afterwards the groat evening fall commenced. It thus completed a double oscillation during tho 21 h. The specific name given to this plant by Ruiz and Pavon, indicates that in its native arid homo it is affected in some manner by the dryness or dampness of the atmoRphcre. * In the Botanic Garden at Wiirzburg, thoro was a plant in a pot out of doors which was daily watered, and another in the open ground which was never watered. After some hot and clry weather there wns a. great difference in the state of the leaflets on these two plants; those on the unwatered plant in the open ground remaining half, • • Systemn. Veg. Florre Peruvianre et Chilensis,' tom. i. p. 95, 1798. We cannot understand the account given by tho authors of tho behaviour of this plant in its native . home. There is much about its power of foretell:n.g changes in the weather; an~l1t appears as if the brightness of the sky Iargc•ly dderJ?ined thll open· ing nud closing of the leaflets. CHAP. VII. SLJ~EP OF J_, EAVES. or even quite, closed <luring tho day. But twigs cut from this hush, with their ends standing in water, or wholly immersed. iu it, or kept in damp air under a boll-glass, opened their leaves though exposed to a blazing sun; whilst those on the pla11t in the ground rcma~ncd. clo ~d.. Tho lo~wc · ou this same plant, after some heavy nun, r~mamed open for two days; they the11 became half closed d.urwg two days, ancl after an adilitionnl day were quite closed. Tllis plant was now copiously watered and on the following morning the leaflets w ro fully ex~ panded. The other plant growing ill a pot, aft r having bec11 exposed to heavy rain, was placed LcfOl'c a winclow iu the LaLoratory, with its leaflets open, and they remained so durin<• tlH~ daytime for 48 h.; but after an additional day were half clo ·e;d. The plant was then watered, and t.he lcafiets on tho two followinv days remained o~en. 0~ tho third day they were again half closed, but on bemg agam watered remained open during the two next days. From these several fact wo may conclude that the plant soon feels the want of water; and that as soon as this occur~, it. partially or qui to closes its leaflets, which in their the~ nnbncated condition expose a small surface to evaporation. It IS therefore proLable that this sleep-like movement, which occurs only ~ben the ground i~;; dry, is an adaptation against the loss of mmsture. t ~.bush about ~ feet in height, a native of Chili, which wa. ,hickly c?vered With leaves, behaved very differently, for duriq; fhB day It never clo ed its leaflets. On July 6th the earth i;t ith e smal.l pot in w b I·c h I· t grew appcarC:d extremely dry, and t~ewas given a very litt.le water. Afttr :.n and 22 days (ou did!~!h an~ 28th), clurmg the whole of which time the lJlttut tl h receive a drop of water, the leaves b gau to droon hut 1ey s owed no · f 1 · . ["'' almost i . Signs o c osm()' dul'lllg the day. It a!Jpear d have k ncre~Ible. tha~ any plant, except a ile hy oue, could a road ep~ ahve m SOil so dry, which re ·cmb1ed the dust on rei! ff. n the 29th, when the bush wa · haken some lewec· 11 o and th · · ' < ,, It was'there e remammg ones were unable to sleep at night. theeve . fore moderately w~tored, as well as syringed, lu.te in as ever~~~ On. the next mommg (30th) the bush looked as f1·el:lh thl4t a 'sm at mght tho. leaves went to sleep. It may be added by means~~ branch ~bile growing on the bush was enclo ed, bottlehalffulto;ur~am. of bladder, dur.ing.l3. days in a large intense! dr . quiCklime, so that. the a1r w1thm must have been Y Y, yet the leaves on this Lmnch dicl not sutl'er iu the |