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Show 22 CIRCUMNUTATION OF SEEDLINGS. CrrAl'. I. d d . . cr 28 h as shown in Fig. 11. It moved cotyl was observe ur.mb f ., . ht and to left in tho figure in all directions ; the hnes rom rig r 1 t being parallel to the blades of t~e cotyledons. r :: af? ~~e1 distance travelled from side to side by . tho su~mi ? b t .2 of an inch. but It was Impossible to hypocotyl was ath?uh d as the m~re obUquoly the plant was he accurate on IS ea • a· t viewed, after it had moved for some time, the more the IS ances were exaggerated. · f tl t We en d eavoure d to Obsn~· r·ve the circumnutatwn 0 10 co d.y - ledons but as they close together unless kept exposed to .n. mo .c-rately l)right light, and as the hypocotyl is extremely helw.tropiC, Fig. 12. Gossupium: c1rcumnu· tation of hypocotyl, traced on a horizontal glass, from 10.30 A.l\1. to 9.30 A.M. on following morning, lJy means of a filan; eut fixed across its summit. Movement of bead of filament magnified about twice; seedling illuminated from above. the necessary arrangements wme too troublesome. We shall recur to the nocturnal or sleep-movements of the cotylodons in a future chapter. Gossypium (var. Nankin cotton) (Malvacere).- The circumnutation of a hypocotyl was observed in the hot-house, but the movement was so much exaggerated that the bead twice passed for a time out of view. It was, however, manifest that two somewhat irregular ellipses were ne~rly completed in 9 h. Another seeclh~g, H in. in height; was then observed durmg 23 h.; but the observations were not made at sufficiently short intervals, as shown by the few dots in Fig. 12, and the tracing was not now sufficiently enlarged. Nevertheless there could be no doubt n.bout the circumnutation of the hypocotyl, which described in 12 h. a figure representing three irregular ellipses of unequal sizes. . The cotyledons are in constant movement up and down dur~ng tho whole day, and as they offer the unusual case of movmg downwards late in the evening and in tho early part of the night, many observations were made on them. A filament was fixed along the middle of one, and its movement traced on a vertical glass; but the tracing is not given, as the hypocotyl was not secured so that it was impossible to distinguish clearly between its mo~ement and that of the cotyledon. The cot!ledons rose from 10.30 A.M. to about 3 P.M.; they thon sank till 10 P.M., rising, however, greatly in the latter part of the night. CHAP. I. GOSSYPIUM. 23 The angles above tho horizon at which the cotyledons of another seedling stood at different hours is recorded in the following short table:- Oct. 20 2.50 P.M. 4.20 , , 5.20 , " 10.40 " Oct. 21 8.40 A.M. • • 11.15 " 9.11 P.M. 25° above horizon. 22° " " 35° " 10° below horizon. The position of the two cotyledons was roughly sketched at various hours with tho same general result. · In tho following summer, the hypocotyl of a fourth seedling was secured to a little stick, and a glass filament with triangles of paper having been fixed to one of the cotyledons, its movements were truced on a vertical glass under a double skylight in tho house. The first dot was made at 4.20 P.M. June 20th; and the cotyledon fell till 10.15 P.M. in a nearly straight line. Just past midnight it was found a little lower ancl somewhat to one side. By the early morning, at 3.45 A.M., it had risen greatly, but by 6.20 A.M. had fallen a little. During the whole of this day (21st) it fell in a slightly zigzag line, but its normal course was disturbed by the want of sufficient illumination, for during the night it rose only a little, and travelled irrognlarly during the whole of the following day and night of June 22nd. The ascending and descending lines traced during tho three days did not coincide, so that the movement was one of circumnutation. 'rhis seedling was then taken back to tho hot-house, and after five days was inspected at 10 P.M., when tho cotyledons were found hanging so nearly vertically down, that they might justly be said to have been asleep. On the following morning they had resumed their usual horizontal position. 0'.1:atis rosea (Oxalidcre).- Tbe hypocotyl was secured to a little stick, and an extremely thin glass filament, with two triangles of paper, was attached to one of the cotyledons, which was ·15 inch in length. In this and the following species tho end of the petiole, where united to the blade, is developed into a pulvinus. The apex of the cotyledon stood only 5 inches from the vertical glass, so that its movement was not greatly exaggerated as long as it remained nearly horizontal; but in the course of the day it both rose considerably above and fell beneath a ·horizontal position, and then of course the movement was much exaggerated. |