OCR Text |
Show 224 CIRCUMNUTATION OF FLOWER-STEMS. CuAP. IV. two smaller ellipses in the course of 24 h., yet tho chief seat of movement lies in the sub-peduncles, which ultimately bend vertically downwards, as will be described in a futuro chapter. The peduncles of Oxalis acetosella likewise bend downwards, and afterwards, when tho pods are nearly mature, upwards; and this is effected by a circumnutating movement. It may be seen in the above figure that the flower-stem of 0. carnosa circumnutated during two days about the same spot. On the other hand, the flower-stem of 0. sensitiva undergoes a strongly marked, daily, penodical change of position, when kept at a proper temperature. In the middle of the day it stands vertically up, or at a high angle ; in the afternoon it sinks, and in tho evening projects horizontally, or almost horizontally, rising again during the night. This movement continues from the period when the flowers are in bud to when, as we believe, the pods are mature: and it ought perhaps to have been included amongst the so-called sleep-movements of plants. A tracing was not made, but the angles were measured at successive periods during one whole day; and these showed that the movement was not continuous, but that tho peduncle oscillated up and down. We may therefore conclude that it circumnutated. At the base of the peduncle there is a mass of small cells, forming a well-developed pulvinus, which is exteriorly coloured purple and hairy. In no other genus, as far as we know, is the peduncle furnished with a pulvinus. The peduncle of 0 . 01'tegesii behaved differently from that of 0. sens'itiva, for it stood at a less angle above the horizon in the middle of tho day, than in the morning or evening. By 10.20 P.M. it had risen greatly. During the middle of the day it oscillated much up and down. Trifolium subterraneum.-A filament was fixed vertically to the uppermost part of the peduncle of a young and upright flower-head (the stem of the plant having been secured to a stick); and its movements were traced during 36 h. Within this time it described (see Fig. 92) a figure which represents four ellipses ; but during the latter part of the time the pedunol.e began to bend downwards, and after 10.30 P.M. on the 24th Jt curved so rapidly down, that by 6.45 A.M. on the 25th it stood only Hl0 above the horizon. It went on circumnutating in nearly the same position for two days. Even after the :fl.ower-hea~s have buried themselves in the ground they continue, a~ Will hereafter be shown, to ciTcumnutate. It will also be seen m th~ next chapter that the sub-peduncles of the separate flowers 0 CHAP. IV. CIRCUMNUTATION OF FLOWER-STEM . 225 Trifol·ium repens circumnutate in a complicate 1 1 · several days. I may add that the gynophore of~ ta~ocm~~,ss ~tt ycp ougncenag, Fig. 92. .10~30':J!.m.24~n '¥ Trif~lium subterraneum : main ' . . . . cncumnutation traceu I fl~" el -peuuncle, dlummateu from above to 10.30 P.M. 24th~ on tonzontal glass, from 8.40 A.M. July 23ni vwehritcihc allolyo ksd oe xact! Yl ~'k e ~peduncle, C.i rcumnutates whilst growinO' ground. wnwar s, m oTder to bury the young pod in th~ obTsherev medo. vbeumt etnbt s of dt he fi ower~ of Cyclamen P ersicurn were not much I.n ' len()'th e pe d unl cle , w. lulst the po d I·S l.cO rrm• ng. m• crea.ses movement. A ' an )OWS Itself down by a circumnutating Hinch in len tKoung pcd~nclo of Maumnilia sernperjforens, and it mado 4~ , was carefully observed during a whole day each at an a 2 narrow, vertical, inegular and short ellip;es' ""J vera go rate of about 2 1 '>~ ' ¥VUUncle described d . 1 · ... o m. An adjoining ellipses • A a· urmg the same time similar thouo·h fewer . ccor mg to Sachs t the flower-stems ; hilst ocrrowin o.' • 'Th - - ' b o• of Climb' Movements and Habits mg Plants,' 2nd ooit., 18t7 5',T pe. x6t8-B. ook of Botany,' 1875, Q |