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Show 498 l\IODIFIED OlHCUMNUTATION. CHAP. X. f.iocn how gradually chc. umnutation be'c omes clm' no-c<lJ· 11 t ~"' oapogeo-i Fig. 184: ~ropiSm,_ under circumstances to be specified m each mstance. \ ,• ~ I r 1 r I ' I t I 8 . Rnb1~s idc~'us (hybrid).-A yon11g plant, 11 ~ mcl:es m llmght, p;rowiJJ p; in a pot, wn~ placed Vl honzontally; aud the upward movement was t traced durin~ nca:·ly 70 h.; hut the plant, cf) ~ thot:g~ growing v1p;orously, was not highly -g] sensitive to apogcotrollism, or it waR not ~ rn Cttpablo of quick movement, for during tho ~ 1 above time it rose only G7°. We may sec in -:<";) ·;::; the diagram (Fig. Hl4) that during tlw first ~F ~ day of 12 h. it rose in a nearly straight line. ·~ ...:::: ;:; ."" When placell horizon tn,ll y, it was ovitlently ~ ~ eircmnnuta,ting, for it l'O.'e at first a little ~n~ notwithstanding the weight of tho ::;tom, aU<l o;; ~ then sank clown; so that it cli<l not. start on .~ o its pcrn1anen.tly lllJWarc.l courso until 1 h. "E~ ~ a:l 25 m. bad elapsed. On the second clay, by ~ ~ which time it had risen considerably, and ~] when apogeotropism acted ou it with somewhat ~ ~ less power, its course during 1 5~ h. wa clearly ~~rt zig'l;ag, aud the rate of the upwanl movement ~ . was uot eqnahle. During tho third day, also ,:: :J of 1 5~ h., when apop;eotropiF>m acted on it ~ ~ with still loss power, the stem plain ly circum- ~ ~ nutated, for it moved U.mi11p; 1his day 3 times ~ ~ up and 3 times down, 4 tim s to tho left and E .3 4. to tJ1e right. But the coursu was so complex -5.~ that it conld hardly be traee(l on the glass. ~ ,.... We can, however, see that tho successively ~ ~ fornJcd irregular eJJjpscs l'OSO J1ighcr aud b/Jro ~;;;; higlwr. Apogeotropism continued to act on ;:; ::1 the fom·th morning, as tho stem was still ~ ,~ ri. ·ing, though it now stood only 23° from the i~ perpendicular. In this diagram the several 6,.... stages may be followed. by which an almost rectilinear, upward, apogcotropic comsc first becomes zigzag, and. then changes in~o a circumnutating movement, with most oi the successively formed, irregular ellipses directed upwards. Lilium auratum.-A plant 23 inches in height was })laced Cm.P. X APOGEOTROPISM. horizontally, and the upper part of tho stem rose 58° in 4.6 h., in tho manner shown in the accom-panying diagram (Fig.185). Wo hero Fig. 185. see that during the whole of the 1 second day of 15~ h., the stom plainly y circumnutated whilst bonding u pwttrds through apogeotropism. It had still to rise considerably, for when the last dot in the figure was made, it stood 32° from an upright position. Pliataris Canariensis.-A cotyledon of this plant (1 · 3 inch in height) has already been described as rising in 4 h. 30m. from 40° beneath tho horizon into a vertical position, passing through an angle of 130° in a nearly straight line, and then abruptly beginning to circumnutate. Another somewhat old cotyledon of tho same height (but from which a true leaf had not yet protruded), was similarly placed at 40° beneath the horizon. For the first 4 h. it rose in a nearly straight course (Fig. 186), so that by 1.10 P.M. it was highly inclined, and now apogeotropism acted on it with much loss power than before, and it began to zigzag. At 4.15 P.M. (i.e. in 7 h. from the commencement) it stood vertically, and afterwards continued to circum-nutate in the usual manner about the same spot. Here then we have a graduated change from a straight up-ward apogeotropic course into circum- Litinm uuratnm : apogconu~ ation, instead of an abrupt change, tropic movement of stem, as In the former case. traced on a vertical glass Avena sativa.-The sheath-ll'ke coty- during 2 days and 2 1 d nights, from 10.4:0 A.M. e ons, ~hilst young, are strongly apo- March 18th to 8 A .M. geotropic; and some which were placed 20th. Figure r educed to at 45° beneath the horizon rose !:lOo 1.n one-half of the original 7 8 scale. 0~ h. in lines almost absolutely straight. An oldish cotyledon, from which the first loaf began to 2 K 2 |