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Show 60 CIRCUMNUTA'fiON OF SEEDLINGS. CnA1'. I. After a time the apex is drawn out of tho empty seell-coats, and rises up, forming a right angle, or moro commonly a Btill larger angle with the lower part, and occaFJiona.lly the whole becomes nearly straight. The conical protuberance, which originally formed the crown of the arch, is now seatecl on one side, and appears liko a joint or knee, which from acquiring chlorophyll becomes green, and increases in si~e. In l'<"trely or never becoming perfectly straight, these cotyledons differ remarkl. tbly from tho ultimate condition of tho arched hypocotyls or epicotyls of dicotyledons. It is, also, a singular circumstance that tho attenuated extremity of the upper bent portion invariably withers and dies. A filament, 1·7 inch in length, was affixed nearly upright beneath the knee to . the basal ::md vertical portion of a Fig. 47. Allium cepa: circumnutation of bnsul half of arched cotyledon, traced in darkness on horizontal glass, from 8.15 A.M. to 10 P.M. Oct. 31st. Movement of bead magnified about 17 times. cotyledon; and its movement.· wore traced during 14 h. in the usual manner. Tho tracing here given (Fig. 47) inclicates circumnutation. Tho movement of the upper part above the lme·e of the f'amc cotyledon, which projected at about an angle of 45° above the hori11on, was observed at the samo timo. A filament was not affixed to it, but a mark was placed beneath tho apex, which was almost white from beginning to wither, and its movements were thus traced. Tho figure described resembled pretty closely that above given; and this shows tlw,t the chief seat of movement is in the lower or basal part of the cotyledon. Asparagus r~fficinaUs (Asparagero).The tip of a straight plumule or cotyledon (for we do not know which it should be called) was found at a depth of ·1 inclt beneath the surface, and the earth was then removed all round to the depth of ·3 inch. A glass filament was affixed obliquely to it, and the movement of the bead, magnified 17 times, was traced in darkness. During the first 1 h. 15m. the plumule moved to the right, and during the next two hours it returned in a roughly parallel but strongly zigzag course. From some unknown cause i't had grown up through the soil in an inclined direction, and now through apogeotropism it moved during nearly 24 h. in .CHAP. l. ASPARAGUS. 61 the same general dh·ection, but in a slightly zig11ap: manner; until it became upright. On tho following morning it changed its course completely. There can therefore hardly bo a doubt that the plumule circumnutatos, wl1ilst buried beneath the ground, as much as tho pressure of the surrounding earth will permit. The surface of tho soil in the pot was uow covered with a thin layer of very fine argillaceous sand, which wa. kept clamp; and after the tapering seedlings had grown a few tenths of an inch in height, each was found smrounded by a little opo~1 space or circular crack; and this could be accounted for only by their having circumnutated and thus pushed away the sand on all sides ; for there was no vestige of a crack in any other part. In order to prove that there was circumnutation, the move- Fi~. 48. .\.. B. Asparagus o.fficinalis: circumnutation of plumules with tips whitened and marks placed benc~th, traced on a horizontal gln ss. A, young plumule; move~1.ent traced from 8.30 A.i\1. Nov. 30th to 7.15 A.j\f. next morning ; mag~1tied about 35 times. ll, older plumule ; movement tra(;ed from 10.1;) .A..l\L to 8.10 P.M. Kov. 29th; ma<rnified 9 times Lut here reduced to one-half of original scale. "' ' mcnts of five seedlings, varying in height from ·3 inch to 2 inches, were traced. They wero placed within a box and illuminated from ~bove; but in all five cases the longer axes of the figures ~escnbed were directed to nearly tho samo point; so that more ~ght seemed to have como through the glass roof of the green-ouse on one side than on any other. All five tracings resembled each other to a certain extent, and it will suffice to give two of them. In A (Fig. 48) the seedling was only ·45 of an |
