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Show 274 MODIFIED CIRCUMNUTATION. CHAP. V. {i!)~)'/U Fig. 123. ,\~ 1(Jq.· 6".i'S'o'.m..l11~~ s· !J•p.ut.t31!1 together. At tho same time tho loop beca.mo open and wa.s thus reconverted into a hook, and this apparently was effected by tho geotropic movement of the apex in 01 po ition to epinasty. In the ca.se of Am]1elopsis hedemcea weight plays, as far as wo c~uld judge, a more important pa.rt in the hooking of the tip. . In order to ascertam whether the shoots of .A. tricuspidata in straightening themselves under the combined action of hyponasty_ancl a pogeotropism moved m a simple straight course, or whether they circumnutated, ()"lass filaments were £xed to the crowns of four hooked tips standing in their natural position; and the movements of the filaments wore tra.ced on 11 vertical glass. All four tracings resembled each other in a general manner ; but ~o will give only one (see FJg. 122, p. 273). The filament rose at first, which . shows that the hook was st~·aJghten1 · ng itself. it then zigzagged, moving a'. h.t tle to the left between 9.25 A.M. and 9 P.M. From this latter hour on tl~e 13th to 10.50 A.M. on the fo- Smithia Pfttndiz: ltypouastic movem ~ nt of the cUl'ved summit of a stem, whilst straightening itsel f, traced from 9 A 111 July lOth to 3 P.l\1. 13th. Apex 9i inl'hes from the vertical glass. Diagr:tm reduced to one-fif'~h of original scale. Pl:tnt illumm:ttcd through skylight; temp.17!0 - 19° C. lowing moming (14t~) b!~~ hook continued to_ strm~ed n 't lf and then zigzagb. 1 se ' tho nght. short distance to 40 M But from 1 P.M. to 10. r. t on the 14th the moYemen CHAP. v. EPINASTY AND liYPO~AS'rY. 275 was reversed and the shoot became moro hooked. Dnring the night, after 10.4.0 P.M. to 8.15 A.M. on tho 15th, tho hook again opened or straightened itself. By this time the glass filament had become so highly inclined that itH movements could no longer be traced with accuracy; and by 1.30 P.l\r. on this Ramo day, the crown of the former arch or hook had hecome perfectly straight and vertical. Thoro can therefore be no doubt that the straightening of the hooked shoot of this plant is effected by the circumnutation of tho arched portion- that is, l>y growth alternating between the upper and lower surface, hut preponderant on the lower surface, with some little la.tcral movement. We were enabled to trace the moverucnt of another stra.ightening shoot for a longer period (owing to its slower growth and to ita having been placed further from the vertical gla. ~),namely, from the early morning on July 13th to late in the evening of the 16th. During the whole daytime of tho 11th, the hook . traighteneditaelf very little, but zigzagged and plainly circumnutatecl about nearly the same spot. By tho 16th it had become nearly straight, and the tmcing was no longer accurate, yet it was manifest that there was still a considerable amount of movement both up and down and laterally; for the crown whilst continuing to straighten itself occasionally became for a. , hort time dmaoyr. e curved, causing the filament to de cend twice during the .Smithia Pjundii.- The stiff terminal shoots of this Legum~ ous water-plant from Africa project so as to ma.ke a. rectangle With the stem below; but this occurs only when the plants arc growing vigorously, for when kept in a cool place, the ummits of the stems become stra.ight, u.s they likewise did at the clo o ofthe.gr?wing season. 1'he direction of tho l'ectangularly bent part Is mdependent of the chief source of light. But from observing the effects of placing plants in the da.rk, in which ~several shoots became in two or three days upright or nearly upnght, and when brought hack into the light again became ~ectangular!y curved, we believe that the bending i. in 11art ue.to apheliotropism, apparently somewhat opposed by apo~coatro sphloSoint ,d On the other hand, from observing the effects of tyin..o,. led to ?Wnwards, so that tho rectangle faced upwards, we are th believe that tho curvature is partly due to opina ty. As the ~tangularly b~nt portion of a.n upright stem grow. older, he ower part straightens itself; and this is effected throuO'h Y!Xlnasty. He who has read Sachs' recent Essay on the ve1·tical T 2 ,,11 "·.i,!,,:: ,.' :)lr .. ! ·:~ |
