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Show 506 MODIFIED CIRCUMNU'l'ATTO:N. OllAr. X. In order to trace this npward movement, a filament was fixed to a snb-pcclunclo bearing a capFmlo ncal'ly ripe, which was beginning to l)oncl upwar<ls hy tho two moans jnst described. Its com·so was traced (sec C, Fig. 188) during 53 h., hy which time it had become nearly upright. Tho course ·is seen to be strongly zigzag, together with some little loops. We may therefore conclude that tho movement consists of modified circumnutation. Tho several species of Oxalis probably profit in the following manner by their sub-peduncles firf:>t bcncling downwards and thou upwards. They arc known to scatter their seoclc:; by the bursting of the capsule; tho walls of which arc so extremely thin, like silver papor, that they would oaf>ily be permeated by min. But as soon as tho petals wither, tho sepals rise up and enclose tho young capsule, forming a l)Orfeet roof over it as soon as the sub-peduncle has bent itself dowuwanls. By its subsequent upwa rd. movement, tho capsule stands when ripe at a greater height above tho ground by twice the length of the sub-peduncle, than it did when dcpmHlcnt, and i thus able to scatter its seeds to a greater distance. Tho sepals, which enclose the ovarium whilst it is young, present an adJitional adaptation by expanding widely when tho seeds arc ripe, so as not to interfere with their dispersal. 1n the case of O:ralis aretosella, tho capsules arc said sometimes to hmy themselves under loose leaves or moss on tho ground, but t his cannot occur with those of 0 . car11osll, as tho woody stem is too high. Uxalis acetosella.-Tho peduJJclos arc fumi1>heu with a joint in --~· .. l ~>(I ~--~> ~~~~.) Z---/ ~/ Oxalis rrcetosella: course pursu e<l by the upper part of a r ;.dunel c, ':hi;~~ rising, traced from 11 A.M. June 1st to 9 A.M. 3rd. ~1gurc hcJe cluced to one-half of the ori ginal scale. the middle, so that tho lower part answers to the mam· peel uncle ' CuAr. X. APOGEOTROPISl\L 507 and the upper part to one of tho sul)-pedunclos o~ 0. crwn~.gct. The upper part bends clownwar<ls, after tho flower l1as ~o~un to wither, and the whole peduncle thm: forms a J1ook, that this ben<ling is due to opinast.y we may 1~for from tl1e case of 0 car11 osrt. When tho pod IS nearly r1po, tho upper part st~aightens itself and becomes erect ; a:nd this is duo to hy~onasty or apogeotropism~ or both combmcd, ancl not to h~ho-t ·sm for it occurred m darkness. The short, hooko i part of rop1 , · d 1 · the peduncle of a cleistogamic flower, beanng a po ncar y ~1pe, was observed in the dark during throe days. ~he apex of tho d at first pointed perpcndicul::trly down, but m the course of ~~ree days rose 90°, so that it now projected horizo~tally. Tho course during the two latter days is shown. in ~1?. 18~; and it may be seen how greatly tl1o poclunclo, wh1lst ns~ng, CJrcumnutated. The lines of chief movement were nt nght angles to the plane of the originally hooked part. ~~o tracing was not continued any longer ; but after two adcbtwnal days, the peduncle with its capsule had become straight and stood upright. . Concluding Remarks on Apogeotropzsm.-When apo-geotropism is rendered 1y any means fcc 1!c, it a?ts, as shown in the several foregoing cases, by Increasing the always present circumnutating movcm nt in a direction opposed to gravity, and 1y diminishino·_that in the direction of gravity, as well as that to mthcr side. The upward movement thus becomes un qual in rate, and is sometimes interrupted by stationary periods. Whenever irregular ellipses or loops are still formed, their longer axes arc almost always directed in the line of gravity, in an analogous manner as occurred with heliotropic movements in ref renee to the light. As apogeotropism acts more and more energetically, ellipses or loops cease to be formed, and the course becomes at first strono·ly, and then less and less zigzag, and finally rectilinear. From this gradation in the nature of the movement, and more especially from all growing parts, which alone (except when pulYini are present) are acted on by apogeotropism, con- |