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Show 44 CIH.CUMNUTATION OF SEEDLINGS. CHAP. I. their cotyledons for tho first time <.luring tho day,-one to tho extent of 90° and tho other rather more; they remained iu nearly tho same position until 10.4.0 P.M. ; but by 7 A .M. on tllo following morning tho one which had been previously open to the extent of 90° had its cotyledons vertical and. comploto1y shut; the other seedling had thorn nearly shut. Later in the morning they opened in tho ordinary manner. It appears therefore that the cotyledons of this plant close and open at somewhat different periods from those of the foregoing species of the allied genera of Cucurbita and. Lagonaria. Opuntia basilaris (Cactcro).-A seedling was carefully ob- Fig. 31. Opuntia basilaris: conjoint circum nutation of hypocotyl nnd cotyledon; filament fixed longitudinally to cotyledon, and movement traced during 66 h. on horizontal glass. Movement of the terminal bead magnified about 30 times, here reduced to onethird scale. Seedling kept in hot-house, feebly illuminated from above. served, because ('.onsidoring it8 appearance and tho nature of the mature plant, it seemed very unlikely that either tho hypocotyl or cotyledons would circumnutato to an appreciable extent. The cotyledons were well developed, being · 9 of an inch in length, · 22 in breadth, and ·15 in thickness. The almost cylindrical hypocotyl, now bearing a minute spinous bud on its summit, was only ·45 of an inch in height, and ·19 in diameter. The tracing (Fig. 31) shows tho combined. movement of the hypocotyl and of one of the cotyledons, from 4.45 P.M. on May 28th to 11 A.M. on tho 31st. On tho 28th a nearly perfect o~lipso was completed. On the 30th tho hypocotyl moved, from some unlmown cau e, in the same general direction in a zigzag line; but between 4.30 and 10 P.M. almost completed a second small ellipse. The cotyledons move only a little up and down: thus at 10.15 P.M. they stood only 10° higher than at noon. Tho chief seat of movement therefore, at least when tho cotyledons are rather old as in the present case, lies in tho hypocotyl. The ellipse described on the 29th had its longer axis directed at nearly right angles to a line joining the two cotyledons. The ~ctual amount of movement of the bead at tho end of the CnAP. I. PH.IMULA. 45 filament was, as far as could be ascertained, about ·14 of an inch. 1/eUanthus annuns (Compositre).-The upper part of tho hypocotyl moved during tho day-time in tho course shown in tho annexed figure (Fig. 32). As the line runs in various directions, crossing itself several times, tho movement may be considered as one of circumnutation. The extreme actual distance travelled was at least ·1 of an inch. Tho movements of tho cotyledons of two seedlings were observed; one facing a northcast window, and tho other so feebly illmpinatcd from above as to be almost in darkness. They continued to sink till about noon, Fig. 32. /---------:--?)\ . ~/ J J IIeliantltus onnttn ~ : circumnutation of hypocotyl, with filament fixed across its summit, traced on a horizontal glass in darkness, from 8.45 A.M. to 10.45 l'.M., and for an hour on following morning. Movement of ucad magnified 21 times, here reduceu to one-half of original scale. when they began to rise; but between 5 and 7 or 8 P.M. they either. sank a little, or moved laterally, ancl then agair. began to nse. At 7 A.M. on the following rooming those ov.. the plant before tho north-cast window had opened so little that they stood at an anglo of 73° above the horizon, and were not observed any longer. Those on the seedling which had been kept in a1most complete darkness, sank duriuo· tho whole day, witho:1t rising about micl-day, but rose durin~ tho night. On the thll'd and fourth days they continued sinldn()' without any alternate ascending movement; and this, no d~ubt, was due to the absence of light. Primula Sinensis (Primulaccre).-A seedling was placed with tho two co~yleclons parallel to a north-cast window on a day when tho hght was near1y uniform, and a filament was affixed to one of them. From observations subsequently made on another seedling with the stem secured to a stick, the greater part of tho movement shown in tho annexed figure (Fig. 33), must. have boon that of the hypocotyl, though tho cotylcdonR cortarnly move up and down to a certain extent both dnring tho day and night. Tho movements of tho same soodliug wore tra£0d |
