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Show 50 CIRCUMNUTATION OF SEEDLINGS. CHAP. I. Nolana prostrata (Nolane~).- T?e movements wer~ not traced, but a pot with seedlmgs, which had. been kept :n the d k ~ an hour was placed under the miCroscope, w1th the ar 1or ' d' · · 11 J micrometer eye-piece so adjusted that each IVISIOn equa ect _1-th of an inch. The apex of one of the cotyledons crossed ;~ther obliquely four divisions in 13 minutes; it was .also sinking, as shown by getting out of focus. The seedlings wore again placed in darkness for another hou:, and the ape~ now crossed two divisions in 6 m. 18 s.; that IS, at very ne.arly the same rate as before. After another interval of un hour m dark-ness, it crossed two divisions in 4 m. 15 s., there- Fig. 37. fore at a quicker rate. In t.he afternoon, aft?r a longer interval in the dark, the apex was mot~onless, but after a time it recommenced movmg, though slowly; perhaps the room was too cold. Judging from previous cases, there _can hardly be a doubt that this seedling was mrcumnuta- Solanum lycopersicum: circumnutation of hypocotyl, with filament fixed across its summit, traced on horizontal glass, frOlll 10 A.M. to 5 P.M. Oct. 24th. Illuminated ob-liquely from above. Move-ment of bead magnified about 35 times, here reduced to onethird of original scale. ting. Solanum lycopersicum (Solanere).-The move-ments of the hypocotyls of two seedling tomatoes were observed during seven hours, and there could be no doubt that both circumnutatecl. They were illuminated from above, but by an accident a little light entered on. one sicl~, and in the accompanying figure (Fig. 37) 1t may be seen that the hypocotyl move~ to this side (the upper one in the figure), makmg small loops and zigzagging in its course. The movements of the cotyledons were also traced both on vertical and horizontal glasses ; their angles with the horizon were likewise measured a~ ~ various hours. They fell from 8.30 A.M. (October 17th) to about noon; then moved laterally i_n a zigzag line, and at about 4 P.M. began to nse; they continued to do so until 10.30 P.M., by which hour they stood vertically ancl were asleep. At what hour of the night or early morning they began to fall was not ascertained. Owing to the lateral movement shortly after mid-day, the descending and ascending lines did not coincide, and irregular ellipses were described during each 24 h. The regular periodicity of these movements is destroyed, .as we shall hereafter see, if the seedlings are kept in the dark. CHAP. I. SOLANUM. 51 Solamtm palinacanth~tm.-Several arched hypocotyls rising nearly ·2 of an inch above the ground, but with the cotyledons still buried beneath the surface, were observed, and the tracings showed that they circumnutated. Moreover, in several cases little open circular spaces or cracks in tho argillaceous sand which surrounded the arched hypocotyls were visible, and these appeared to have been made by the hypocotyls having bent first to one and then to another side whilst growing upwards. In two instances the vertical arches wore observed to move to a considerable distance backwards from the point where the cotyledons lay buried; this movement, which has been noticed in some other cases, and which seems to aid in extracting the cotyledons from the buried seed-coats, is due to the commencement of the straightening of the hypocotyl. In order to prevent this latter movement, the two legs of an arch, tho Solanum :palinrteantltttm: circum~utation of an arched hypocotyl, just emergmg from the ground, w1th the two legs tied together traced in darkness on a horizontal glass, from 9.20 A.lii. Dec. 17th to' 8.30 .A.l\f. 19th. Movement of bead magnified 13 times; but the filament which was affixed obliquely to the crown of the arch, was of unusual iength. summit of which was on a level with the surface of the soil were ~ied together ; the earth having been previously I'emoved to a httle depth all round. The movement of the arch during ~7 hours under these unnatmal circumstances is exhibited m the annexed figure. The cotyledons of some seedlings in the hot-house were horizontal about noon on December 13th; a,nd at 10 P.M. had 1·isen to an angle of 27° above the horizon; at 7 A.~r. on the following E 2 |