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Show 278 MODIFIED ClllOUMNUTATION. CHAP. V. up W•n• r·cls , ·R O as to occupy tho same p.o sition relatively t.o the upper part of tho main peduncle as m Tr. r·epens. _This fact alone would render it probable that the movement~ of the sub-dunclcs in Tr. repens wore independent of geotrornsm. Never!~~ oless, to make sure, some flower-heads wore ti?~ to littl~ sticks up ide down aud others in a horizontal pos1L10n; their subpeduncle. ·, however, all quickly Cl~rvecl upwards through . the action of heliotropism. vV c therefore protected Rome flowerheads, similarly secured to stickR, !'rom the light, ancl although some of them rotted, many of thmr sub-peduncles turne~ :cry slowly from their reversed or from their horizontal positiOns, so as to staud in the normal manner parallel to the upper pa:t of the main peduncle. These facts show tl1at tho movement JS iudependent of geotropism or apheliotropism; it must therebe attribute<l to opinasty, which however is checked, at least as long as tho flowers are young.' . by holi?tropism. Most ~f the above flowers were never forhltscd owmg to the cxcluswn of bees; they consequently withered very slowly, and the movements of tho sub-peduncles were in like manner mu?h retarded. To ascertain tho nature of the movement of tho sub-peduncle, whilst bonding downwards, a filament was f-ixed across _tho summit of tho calyx of a not fully expanded. aml aln:ost upnght flower, nearly in the centro of tho hcn.U. 'fhc mam peduncle was secured to a stick close beneath tho head. In order to see the marks on the glass filament, a few flowers had to be cut away on the lower side of tho head.. '!'he ~ower u~~cr observation at first diverged a little from Its upnght positiOn.' ~o. as to occupy the open space caused by the removal of tho adJOlll~ng flowers. 'l.'hiR required two days, after which time a new trac~ng was begun (FiO'. 124). In A we sec the complex circumnutatmg course pursued from 11.30 A.M. Aug. 26th to 7 A.M: on th~ 30th. The pot was then moved a very little to. the n ght, anc tho tracing (B) was continued without interruptiOn from 7 A.M. Aug. 30th to after 6 P.M. Sept. 8th. lt should be observed t~Jat on most of these days only a single dot was made each mormng at the same hour. Whenever the flower was observed careful~y, as on Aug. 30th and Sept. 5th and 6th, it was found to b:hCI~; cumnutatino· over a small space. At last, on Sept. _7 ' began to boon d downwards, and contm. ucd t o d o so until afhte r 6 P.M. on the 8th, and indeed until the mornm· g 0 f tl1 e .9 th ' w en 1 . its movements could no longer be trace d on tl1 c vertiCal gd abss . lt was carefully observed during the whole of the 8th, an Y CHAP. v. EPINASTY AND HYPONASTY. 279 10.30 P.M. it had descended to a point lower down by two-thirdR of the length of the figure as hero given; but from want of spn.ee the tracing has been copied in B, only to a little after 6 P.M. On the morning of the 9th the flower was withered, and the subpeduncle now stood at an angle of 57° beneath tho horizon. H the flower had been fertilised it would have withered mnch sooner, and have moved much more quickly. We thus see that the sub-peduncle oscillated up and down, or circumnutatecl, during its whole downward opinastic course. The sub-peduncles of the fertilised an<l withered flowers of Oxalis carnosa likewise bond downwards through epinasty, as will be shown in a future chapter; and their downward course is strongly zigzag, indicating circumnutation. The number of instances in which various organs move through epinasty or hyponasty, often in combination with other forces, for the most <.liversific<l purposes, seems to be inexhaustibly groat; and from the several cases which have been hero given, we may safely infer that such movements are duo to modified circumnutation. I -,/ .~(1 . ::~ I ,. oli |