OCR Text |
Show 28 CIRCUMNUTATION 0]' SEEDLINGS. CnAr. I. Citrus auranfium (Orange) (Aurantiaceoo?.-The c?tyledons are hypogean. The circumnutation of ~n epiCotyl, whi_ch at_ the close of our observations was ·59 of an mch (15 mm.) _m hmght above the ground, is shown in the annexed figure (F1g. 17), as observed during a period of 44 h. 40 m. Citr/ls aurantium: circumnutation of epicotyl with a filam ent fix ed trans· versely near its apex, traced on a horizontal glass, from 12.13 P.M. on Feb. 20th to 8.55 A.M. on 22nd. The movement of the bead of the filament was at first magnified 21 tim~s, or 10~, in fi gure here ~ i ve n, and afterwards 36 times, or 18 as here given; seedling illummated from above. ..!Esculus hippocastanum (Hippocastaneoo).-Gorminating seeds were placed in a tin box, kept moist internally, with a sloping bank of damp argillaceous sand, on which four smoked glassplates rested, inclined at angles of 70° and 65° with the horizon. The tips of the radicle& were placed so as just to touch the upper end of the glass-plates, and, as they grew downwards they pressed lightly, owing to geotropism, on the smoked surfaces, and left tracks of their course. In the middle part of each track the glass was swept clean, but the margins were much blurred and irregular. Copies of two of these tracks (all four being nearly alike) were made on tracing paper placed over the glass-plates after they had been varnished; and they are as exact as possible, considering the nature of the margins (Fig. 18). They suffice to show that there was some lateral, almost serpentine movement, and that the tips in their downward course pressed with unequal force on the plate.3, as 0IIAP. I. VICIA. 29 the tracks varied in breadth. The more perfectly serpentine tracks made by the radicles of Phuseolus multijlorus and Vicia faba (presently to be described), rende1· it almost certain that the radicles of the present plant circumnutated. Phaseolus multifionts (Legumino~oo). -Four smoked .glass-plates were arranged in the same manner as described under .lEsculus, and the tl'acks left by the tips of four radicles of the present plant, whilst growing downwards, were photographed as transparent objects. Three of them are here exactly copied (Fig. 1\:l). Their serpentine courses show that the tips moved regularly from side to side ; they also pressed alternately with greater or Joss force on the plates, sometimes !'ising up and leaving them altogether for a very short distance ; but this was better seen on the original plates than in the copies. Fig. 18. A. B. ./E1:cnlus Mppocast,mum: outlines of tracks left on inclined glass-plates by tips of radicles. In A the plate was inclined at 70° with the horizon, and the radicle was 1· 9 inch in length, and ·23 inch in diameter at base. In B the plate was inclined 65° with the horizon, and the radicle was a trifle larger. These radicles therefore were continually moving in all directions- that is, they circumnutated. The distance between the extreme right and left positions of the radicle A, in its lateral movement, was 2 mm., as ascertained by measurement with an eye-piece micrometer. Vicia faba (Common Bean) (Leguminosoo ).- Radicle. -Some beans were allowed to germinate on bare sand, and after one had protruded its radicle to a length of · 2 of an inch, it was turned upside down, so that the radic.le, which was kept in damp air, now stood upright. A filament, nearly an inch in length, was Fig. 19. I A. D. c. P!taseolus mult-iflorus: tracks left on inclined smoked glass-plates by tips of radicles in growing downwards. A and C, plates inclined at 60°, B inclined at 68° with the horizon. affixed obliquely near its tip; and the movement of the terminal bead was traced from 8.30 .A.M. to 10.30 P.M., as shown in Fig. 18. The radicle at first changed its course twice |