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Show 40 CIRCUMNUTATION OF SEEDLINGS. CHAP. I. pressed alternately with greater and less force on them. There must, therefore, have been movement in at least two planes at right angles to one another. These radicles were so delicate that they rarely had the power to swoop the glasses quite clean. One of them had developed some lateral or secondary rootlets, which projected a few degrees beneath the horizon; and it is an important fact that three of them left distinctly serpentine tracks on the smoked surface, showing beyond doubt that they had circumnutated like the m&in or primary radicle. But the tracks were so slight that they could not be traced and copied after the smoked surface had been varnished. Jlypocotyl.-A seed lying on damp sand was firmly fixed hy two crossed wires and by its own growing radicle. Tho cotyledons were still enclosed within the seed-coats; and tho short Fig. 29. Cucurbita ovifem: circumnutation of straight and vertical hypocotyl, with filament fastened t;ransversely across its upper end, traced in darkness on a horizontal glass, from 8.30 A.M. to 8.30 P.:M. The movement of the terminal bead originally magnified about 18 times, here only 4~ times. hypocotyl, between the summit of the radicle and the cotyledons, was as yet only slightly arched. A filament (' 85 of inch in length) Wi\S attached at an anglo of 35° above the horizon to the side of the arch adjoining the cotyledons. This part would ultimately form tho upper end of tho hypocetyl, after it had grown straight and vertical. Had the seed been properly planted, the hypocotyl at this stage of growth would. have been deeply buried beneath the surface. The course followed by tho bead of the filament is shown in Fig. 28. Tho chief lines of movement from left to right in the figure were parallel to the plane of the two united cotyledons and of the flattened soed ; and this movement would aid in dragging them out of tho seed-coats, which are held down by a special structure hereafter to be described. The movement at right angles to the above lines was due to the arched hypocotyl becoming more arched as it increased in height. Tho foregoing observations apply to the leg of the arch next to the cotyledons, but CrrAP. I. CUOURDITA. 41 the other leg adjoining the radicle likewise circumnutated at an equally early age. The movement of the same hypocotyl after it had become straight a~d verti~al, ?ut with the cotyledons only partially expanded, IS shown m .Fig. 29. The course pursued during 12 h. apparently ro~Jresonts four and a half ellipses or ovals, with the longer axis of the first at nearly right angles to that of the others. T?o longei· axes of all were oblique to 11 Hne joining t~e opposite coty loclons. ':J:Ihe actual extreme distance from Side to. side over which tho summit of tho tall hypocotyl passed m the course of 1'2 h. was · 28 of an inch. The original figur~ was tr~ccd on a largo scale, and from the obliquity of the lme of VIOW the outer parts of the diagram are much exaggerated. Gotyledons.-On two occasions the movements of the cotyle~ ons we_re tr~ccd o~ a vertical glass, and as the ascending and descendmg hues did not quite coincide, very narrow ellipses were ~ormed;. they therefore circumnutated. Whilst young they nse vertically up at night, but their tips always remain reflexed; on the following morning they sink down again. With a seedling kept in complete darkness they moved in the same manner, fo~ they sank from 8.45 A.M. to 4.30 P.M.; they then began to nse and remained close together until 10 P.M., when they were last observed. At 7 A.M. on the following mornino· they w~re as much expanded as at any hour on the previou~ ~ay. 'lhe cotyledons of another young seedling, exposed to the hg~t, were fully open for the first time on a certain day, but ;ve1c found completely closed at ~A.M. on the followjng morning. They soon began to expand agam, and continued doing so till abot~t 5 P.M. ; they thou began to rise, and by 10.30 P.M. stood :ert10ally and were almost closed. At 7 A.M. on the third mornmg .they were. nearly vert~cal, and again expanded during the day, on t~o fo~rth mornmg they were not closed, yet they opene~ a h:tle m the course of the day and rose a little on the followmg mgbt. By this time a minute true loaf had become developed. Anothe_r ~oedling, still older, bearing a well-developed leaf, had a_ sharp r1gid filament affixed to one of its cotyledons (85 mm: m length), which recorded its own movements on a rov~lvmg drum with smoked paper. Tho observations were made m the ho~-houso, where the plant had lived, so that there was no change m temperature or light. The record commenced at 11 A.M. on February 18th; and from this hour till 3 P.M. the |