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Show 324 :l\fODIFIED CIRCUl\:INUT AT ION. CHAI'. VII. large hall, lighted only from tho roof, did not sleep at night, for in order to do so tho leaves must bo well illuminated dming tho day. Tho cotyledons do not sloop. LinmnnR says that tho loaves of his St'd·" obntilon sink perpendicu larly down at night, though the ])Otioles rise. Prof. Pfeffer informs us thnt tbo leaves of a Malva, alJjed to AI. sylv,stris, rise greatly at night; and this genus, as well as that of Hibiscus, arc included by Linnmus in his list of sleeping plants. .Anoda 11'7'1·.r;htii (Malvaccm).-1'ho loaves, produced l1y very young plmtts, when grown to a modcrrtto size, Riuk n.t night either almost vertically down or to an anglo of about 4.)0 bcnertth the horizon; for there is a considerable degree of variability in the amount of sinking at rught, which depends in part on tho degree to which they hnve boon illuminated during tho drty, But tho leaves, whilst quito young, do not ink down at night, and this is a very unusual circumstance. Tho summit of tho petiole, whore it joins tho hlaclo, is dovolopccl into a pulvinus, and this is present in very young leaves which do not sleep; though it is not so well defined as in older lcav s. Gossypium (var. Nankin cotton, Malva cro).-Some young lea•cs, between 1 and 2 inches in length, borDO by two seedlings 6 and 7 i inches in hciO'ht, stood horizontally, or wore raised a little above tho horizon at noon on July Hth and 9th; but by 10 P.M. they had sunk down to between 68° and 90° beneath the horizon. When the samo plants had grown to double the above height, their leaves stood at night almost or quito vertically dependent. Tho loaves on some largo plants of G. rnat·itinmm and Bruzilense, which were kept in a very badly lighted hot-house, only occasionally sank much downwards at night, and. hardly enough to be called sloop. O.wlis (Oxalidm).- In most of tho species in this large gen~s the three leaflets sink vertically down at night; but as then sub-petioles are short the blades could not assume this position from the want of space, unless they were in some manner ren· dored narrower; and this is effected by their becoming more or less folded (Fig. 127). The angle formed by the two halves of the same leaflet was found to vary in diiferont individuals of several species between 92° and 150° · in three of the best fold ed leaflets of 0. fragrans it was 76°, 74°, and 54o. 1'ho angle iR often different in tho three leaflets of the same lea.f. As tho leaflets sink down at night and become folded, therr lower surfaces are brought ncar together (.See B), or oven into CIIAP. VII. SLEEP OF LEA YES. 325' close conta~t; and from th.is circumstance it might be thought that the obJect o~ the foldmg was the protection of their lower surfaces. If this had ~een the case, it would have formed a strongly marked exceptiOn to tho rule that when tl · d .ffi · h J ' 1ere Is any 1 erence m t o etegrce. o~ protection from radiation of the two surfaces of the leaves, It IS always tho upper surfaco which is the best protected But that tho folding of the leaflets, and consequent mutual approximation of thoi·r· lo wer SUI'1" aces serres merely to allow them to sink down vcrtieully, may b~ Fig. 127. A. n Oxalis acetosella ·. A 1 f f . · 1 ' ea seen ro~ vcrt•cally above; B, diag~·am of leaf as eep, also seen Jrom ' 'c rtically abo,·e. ~~:r:: from ~he fact that when tho leaflets do not radiate plent oef s:rnmlt .of a common p~tiolo, or, again, when there is leafieis sin~o:, flO~ tho sub-potJ.oles not being very short, the the leaf] t f own w~t~1out becommg folded. This occurs with Th e ~ 0 0. sensdwa, Plumierii, and bupletwijolia ere Is no use in . . 0' 1 . . which I . givmo a ong list of tho many species with Rps e.ep hm !,he above noscribcd manner. This holds good or largee C1Je s av1m. g rather fie s h y 1c aves, 1'1 I co those of 0. l'a?'?UJ.~rr those of oe:v;~. I~~ thoRo of 0. Ort ·ge.~ii, or four leaflets lik~ show n ·. ~abdts. There are, however, some species which 0 Signs of sleep · 0 and rubella W . 'VIZ., : pe11trtphylla, tnnntphylla, hir·ta, in some ft. h e WJ.ll now descnbe the natul'e of the movements o e speCies. O:calis aceto.w·lla _ Tb that of the . . . e movomcut of a lea:flet, together with gram (Fi . 1;am . petwle, are shown in the following dia- 7.45 g 8), tlacod between 11 A.M. on October 4th a d ur. on the 5th Aft 53 n rapidly d ' · er · 0 P.M. on tho 4th the lca:flet saul· before i' t an at 7 P.M . . n-1 epond el-:l~ vertJ.c ally. For some time'- course assIu med th1s latto r po.·I· t·J On, I· ts movements could of broke~ I~: i~~1cr d ?e traced on the vertical glass, and tlJe e Iagram ought to be extended much further |