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Show 510 MODIFIED CIROUMNUTATION. CIIAl' . X. several large ellipses during 14 h., as it likewise did on the following clay; bnt (lurino· this whole time it was not in the lett t atfected by apogcotropism. On the other halHl, when bmnch cs of anot her Onemhitaceous plant, E chinocytis lobatct, were fixed in tho clnrk so that the tendrils cl 'prnclccl ben eath the horizon, these began immediately to beU<l upwards, and whil st thus moving they ceased to circumnutate in any plain manner; but as soon as they hacl become horizontal th ey recommenced to rcvol ve cons pi cuousl y. * rl'he tendrils of Passijl01·a gracilis are likewise apogootropic. 1'wo branches were tied down so that their tendrils pointed many degrees beneath the horizon. One was observed, for 8 h., during which time it rose, descriLin ;r two circles, one above the other. The other tendril rose in a moderately straight line during the first 4 h., making however one small loop in its course ; it then stood at about 45° above the horizon, whore it circum· nutated during the remaining 8 h. of observation. A part or organ which whilst young is extremely sensitive to apogeotropism ceases to be so as it grows old; ancl it is remarkabl e, as showing tho incleponclence of this sensitiveness and of the circnmnntating move· ment, that the latter sometimes continnos for a time after all power of Lending from the centro of tho earth has been lost. Thus a seedling Orange Learing only 3 young leaves, with a rath er stiff stem, did not curve in the least upwards during 24 h. whilst extended horizontally; yet it ch·cumnutatcd all the time over a small space. The h ypocoty l of a young seedling of Cassia tara, similarly placed, became vertical in 12 h.; that of an older seedling, l ;l- inch in height, * For details see 'The Movements and Habib:> of Climbing Plants,' 1875, p. 131. CnAP. X. APOGEOTROPISM. 511 became so in 28 h. ; and that_ of anot~cr still ol~ler e u inch in height, remamed honzontal dunng on, ~ ,, d · h' two days, but distinctly circnmnutatcu unng t IS whole time. When the cotyledons of l"'>hal aris or A vena arc laid horizontally, the uppermost part first bends upwards, and then tho lower part; consequently, after the lower part bas become much curved up,:ards, the upper part is compelled to curve backwards In an opposite ducction, in oruer to straighten itself and to stand vertically; and this subsequent straighteninp- process is likewise duo to apogcotropism. The upper part of 8 young cotyledons of Phalaris were made rigid by being cemented to thin glass rods, so that this part could not bend in the least ; nevertheless, the basal part was not prevented from curving upward. A stem or other organ which bcn<ls upwards through apogeotropism exerts considerable force; its own weight, which has of course to be lifted, was sufficient in almost every instance to cause the part at first to bend a little downwards; but the downward course was often rendered oblique by the simultaneous circumnutating movement. The cotyledons of A vena placed horizontally, besides lifting their own weight, were able to furrow the soft sand above them, so as to leave little crescentic open spaces on the lower sides of their bases; and this is a remarkable proof of the force exerted. As the tips of the cotyledons of Phalaris and Avena bend upwards through the action of apogeotropism before the basal part, and as these same tips when excited by a lateral light transmit some influence to the lower part, causing it to bend, we thought that the same rule might hold good with apogeotropism. Consequently, the tips of 7 cotyledons of Phalaris were |