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Show 504 MODIFIBD CI!tCUl\'INU'r A'l'ION. Cl!AP. X. peduncles be~d downwards, and thi~ is dne to epinasty; for ·on two occasiOns when pots were la1d horizontally, the subpeduncles assumed the same position relatively to the main peduncle, as would have been the case if they had remained upright; that is, each of them formed with it an anO'le of about 40°. If they had been acted on by geotropism or apheliotropism (for the plant was illuminated from above), they would have directed themselves to tho centre of the earth. A main peduncle was secured to a stick in an upright position, and one of the upright sub-peduncles which had been observed circumnutating whilst the flower was expanded, continued to do so for at least 24 h. after it had withered. It then began to bond downwards, and after 36 h. pointed a little beneath the horizon. A new figure was now begun (A, Fig.l88), and the sub-peduncle was traced descending in a zigzag line from 7.20 P.M. on the 19th to 9 A.M. on the 22nd. It now pointed almost perpendicularly downwards, and the glass filament had to be removed and fastened transversely across the base of the young capsule. We expected that tho sub-peduncle would have been motionless in its new position; but it continued slowly to swing, like a pendulum, from side to side, that is, in a plane at right angles to that in which it had descended. This circumnutating movement was observed from 9 A.M. on 22nd to 9 A.M. 24th, as shown at B in the diagram. We were not able to observe this par· ticular sub-peduncle any longer; but it would certainly have gone on circumnutating until the capsule was nearly ripe (which requires only a short time), and it would then have moved upwards. The upward movement (C, Fig. 188) is effected in part by the whole sub-peduncle rising in the same manner as it had previously descended through epinasty-namoly, at the joint where united to the main peduncle. As this upward :movement occurred with plants kept in the dark and in whatever position the main peduncle was fastened, it could not have been caused by heliotropism or apogeotropism, but by hyponasty. Besides this movement at the joint, there is another or a very different kind, for the sub-peduncle becomes upwardly bent in the middle part. If the sub-peduncle happens at the time to be inclined much downwards, the upward curvature is so great that the whole forms a hook. The upper end bearing the capsule, thus always places itself upright, and as this occurs in darkness, and jn whatever position the main peduncle may have been secured, CHAP. x. APOGEOTROPISM. 505 the upward curvature ~annot be due to heliotropism or hyponasty, but to apogeotropiSm. ' Fig. 188. ! \ A \ ~ ~~)' \~···- '•,, ____________ _ ~ O:ra/is ca.rnosa: movements of flower-peduncle, traced on a vertical glass: ~' epma~tic downward movement; B, circumnutation whilst dependID~ vertically; C, subsequent upward movement, due to apogeotropism and hypona.sty combined. |