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Show 388 MODIFIED CIRCUMNUT.ATION. CIIAI'. \II. Euphorbin facqnillicejlom (Enphorbiacero). - Mr. Lynch cn,llcd our attention to tho fact that the yonn~ leaves of this plant sleep by depending vertically. Tho thinl leaf from the summit (March 11th) was inclined during tl1e day 30° beneath the horizon, and at night hung verticn,lly down, as did some of the still younger leave·. It rose up to its former level on tho following morning. The fourth and fifth loaves from tho summit stood horizontn,lly during tho day, and sank down at night only 38°. Tho sixth leaf did not sensihly alter its po ition. 'rho sinking movem~nt is duo to tho downward curvature of tho petiole, no part of which exhibits any structure like that of a pulvinus. Early on tho morning of Juno 7th a filament wns fixed longitudinally to a young loaf (tho third from tho summit, and 2~ inches in length), n,ncl its rnove~ents. wer~ traced on a vertical glass during 72 h., tho plant bemg 1llum~nated from above through a skylight. Each cLty the leaf fell m a nearly straight line from 7 A.M. to 5 P.M., after which hour it was so much inclined downwards that tho movement could no longer be traced; and during the latter lXtrt of each night, or ()ttrl.y in tho morning, the leaf rose. It therefore circumnutated m a very simple manner, making a single largo ellipse ?ve.ry 24 h., for the ascending and descending lines did not comc1de. On each successive morning it stood at a loss height th~n on ~he previous one, n.ncl this was probably clue, p~rtly t? th~ mcre~sm~ age of the len.f, and partly to the illuminn.tw_n bom.g msufficieJ~t, for althouo·h the len.ves are very slightly hehotrop1c, yet, acco~dinO' to Mr.~Lynch's and onr own observations, their i1~clinat10n du~·ing tho clay is determined by the intensity of the light .. on tho third cln.y, by which time tlte extent of the descen~wg movement had much clocren.socl, tho line trn.ced was plalllly much more zigzag than ~n n.ny previous clay, an~ it appc:u~~ as if some of its powers of movement were thus expen?ed. 10 p M on June 7th when tho leaf depended vertically, Jts move· ment·~ ·w ere observe'd by n. mn.rk bo.m g placed l) 01 1 ·m d 1·t ' and thJo end of the attached filament was soon to oscillate slowly tu slightly from side to side, n.s well as upwn.rds n.nd downwarcts; .. Phvllcmthtts J.\''i?·ttri (Euphorb 1. accre ) . - Tl1 0 leaflets of uJS c cc * · ·emarkable manner, Plant sleep, n.s described by P1ouer, m n. 1 ' .. 1 8 at apparently like those of Cass1.n ., f or tl1 oy 81· nk downwaltU ·. cJ night tmd twist round, so tl1at their lower surf ace s arc mn * ' Die PcrioLl. Bc,rcg.,' P· 15G. CHAP. VII. SLEEP OF LEAVE '. 3 D outwards. They are furnished, as might hn.ve been expected from this complex kind of movement, with a pulvinus. GYMNOSPERMS. Pinus Nordmanniarw (Conifor::e).-M. Chatin states* thn.t tho leaves, which aro horizontn.l during tho day, rise up at night, so a• to assume a position almost perpondiculn.r to tho branch from which they al'ise; we presume that he here refers to a horizontn.l brilnch. He adds: "En meme temps, ce mouvoment d.' erection cstaccompagne d'un mouvement de torsion imprim6 it la partio basilaire de ln. feuille, et pouvant souvent parcourir un arc do 90 degres." As tho lower surfaces of the loaves are white, whilst the upper are dark groou, the tree presents a widely different appearance by clay and night. The loaves on n. smn.ll tree in a pot did not exhibit with us any nyctitropic movements. We have seen in a former chn.pter that the loaves of Pinus pinaster and Austriaca are continually circumnutn.ting. l\fONOCOTYLEDONS. Thalia dealbata (Cannacom).-The leaves of this plant sleep by turning vertically upwards; they aro furnished with a welldeveloped pulvinus. It is the only instance known to us of a very large leaf sleeping. Tho bln.de of a young leaf, which was as yet only 131 inches in length and 61 in breadth, formed at noon an angle with its tall petiole of 121°, n.ncl at night stood vertically in a line with it, anJ. so hn.d risen 59°. 'l'he actual dis~nce travelled by the apex (tts measured by an orthogonic traci?g) of another large leaf, between 7.30 A.M. and 10 P.M., was 10! mches. Tho circumnutn.tion of two young n.ncl dwarfed leaves, arising amongst the tn.ller leaves at tho base of the plant, was traced on a vertical glass during two dn.ys. On tho first day the a~ex of one, and on tho second clay tho apex of tho other leaf, desenbecl ~etween 6.40 A.M. and 4 P JVr. two ellipses, the longer a.xes of which were extended in very different directions from the hnesrepresenting tho gren.t diurnal sinking and nocturnalrisinomovement. r. ~~~ranta arundin.ru:ea (Cannacoro).-Tho bln.des of the lon.ves, which are furnished with a pulvinus, stand horizontally during "' 'Oomptos Rendus,' Jo.n. 18713, p. 171. |