OCR Text |
Show 276 MODIFIED CIRCUMNUTATION. CnAP. V. and inclined positions of the parts of plants* will soc how difficult a subject this is, and will feel no surprise at our expressing oursel vos doubtfully in this and other such cases. A plant, 20 inches in height, was secured to a stick close beneath the curved summit, which formed rather less than a rectangle with the stem below. The shoot pointed away from the observer; and a glass filament pointing towards the vertical glass on which tho tracing was made, was fixed to tho convex surface of the curved portion. Therefore the descending lines in the figure represent tho straightening of the curved portion as it grew older. Tho tracing (Fig. 123, p. 274) was begun at 9 A.M. on July lOth; the filament at first moved but little in a zip;r.ag line, but at 2 P.M. it began rising and continued to do so till 9 UI.; and this proves that the terminal portion was being more bent downwards. After 9 P.M. on tho lOth an opposite movement commenced, and the curved portion began to straighten itself, and this continued tillll.lO A.M. on tho 12th, but was interrupted by some small oscillations and zigzags, showing movement in different directions. After 11.10 A.M. on tho 12th this part of the stem, still considerably curved, circumnutatod in a conspicuous manner until nearly 3 P.M. on the 13th; but during all this time a downward movement of the filament prevailed, caused by the continued straightening of the stem. By the afternoon of the 13th, the summit, which had originally been deflected more than a right anglo from the perpendicular, had grown so nearly straight that the tracing could no longer bo continued on the vertical glass. There can therefore be no doubt that. the straightening of tho abruptly curved portion of tho growing stem of this plant, which appears to be wholly duo to hyponasty, is the result of modified circumnutation. Wo will only add that a filament was fixed in a different manner across the curved summit of another plant, and the same general kind of movement was observed. Trifol,ium repens.-ln many, but not in all tho species of Tri-folium, as the separate little flowers wither, the sub-peduncles bend downwards, so as to depend parallel to tho upper part of tho main peduncle. In 'J.'r. subtLrraneum the main pedunc~e curves downwards for the sako of burying its capsules, and 1ll this species the sub-peduncles of the separate flowers bend * 'Ueber Orthotrope und Plagiotrope Pflanzentheile ;' ' Arbei-ten des Bot. Inst., in Wiirzburg,' Heft ii. 1879, p. 226. CHAP. v. EPIN ASTY AND IIYPON AS'l'Y. A. Trtiafotl' ium repens: c•u cumnu-mg and epinastic move ~ents ?f the sub-peduncl~ on a smg~e flower, traced a ska l~ertl~al glass uuder y •ght, m A from 1130 A.l\1. Aug 27th . 3oth . · to 7 A 111 i m B fro · · Aug. 30th to ~ 7 .A.M. 6 p l\1 S a httle afte1• · · ept, 8th. Fig. 124. B. 277 |