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Show 26 CIROUMNUTATION OF SEEDLINGS. OnAP. I. placed only 1~ inch from the vertical glass. At 6.40 A.M. it stood horizontally; it then fell till 8.35, and then rose. AltoO'ether in the course of 12 h. it rose thrice and fell thrice, as m~y pe seen in Fig. 15. The great nocturnal rise of tho co.tyledons usually commences about 4 or 5 P.M., and on the followmg morning they are expanded or stand horizontally at about 6 .. 30 A.M. In the present instance, however, the great nocturnal nse did not commence till 7 P.M.; but this was due to the hypocotyl having from some unknown .cause temporaril~ bent. t? the left side as is shown in the tracing. To ascertam pos1t1vely that the 'hypocotyl circumnutated, a mark. was placed at 8.15 P.M. behind the two now closed o.nd vertical cotyledons; and the movement of a glass filament fixed upright to tho top of the hypocotyl was traced until 10.40 P.M. During this time it moved from side to side, as well as backwards and forwards, plainly showing circumnutation; but the ~ovement was small in extent. Therefore Fig. 15 represents fairly well tho movements of the cotyledons alone, with the exception of the one great afternoon curvature to the left. . . Oxalis corniculata (var. cuprea).-The cotyledons nse a't rught to a variable degree above the horizon, generally about 45° : those on some seedlings between 2 and 5 days old wore found to be in continued movement all day long; but tho movements were more simple than in the last two species. This may have partly resulted from their not being sufficiently illuminated whilst being observed, as was shown by their not beginning to rise until very late in the evening. Oxalis (Biophytum) sens1"tiva.-The cotyledons are highly remarkable from the amplitude and rapidity of their movements during the day. The angles at which they stood abov? or beneath the horizon were measured at short intervals of time; and we regret that their course was not traced during the whole day. We will give only a few of the measurements, which were made whilst the seedlings were exposed to a temperature of 22~ 0 to 24~° C. One cotyledon rose 70° in 11m.; another, on a distinct seedling, fell 80° in 12m. Immediately before this latter fall the same cotyledon had risen from a vertically downward to a vertically upward position in 1 h. 48 m., and had therefore passed through 180° in under 2 h. We have met with no other instance of a circumnutating movement of such great amplitude as 180~ ; nor of such rapidity of movement as the passage through HOo m 12m. Th.e cotyledons of this plant sleep at night by rising CHAP. I. TROP JEOL UM. 27 vertically and coming into close contact. This upward movement differs from one of tho groat diurnal oscillations above described only by the position being permanent during the night and by its periodicity, as it always commences late in the evening. Tropmolum minus (?) (var. Tom Thumb) (Troproolere).-The cotyledons are hypogoan, or never rise above tho ground. By removing the soil a buried epicotyl or plumule was found, with its Fig. 16. summit arched abruptly down-wards, like the arched hypocotyJ of the cabbage previously described. A glass filament with a bead at its end was affixed to the basal half or leg, just above the hypogean cotyledons, which were again almost surrounded by loose earth. The tracing (Fig. 16) shows tho course of the bead during 1111: After the last dot given in the figure, the bead moved to a groat distance, and finally off the glass, in the direction indicated by the broken line. This great movement, due to increased growth along the con-cave surface of the arch, was caused 7,t ·opreo l um mm. us (?) : ci. rcum-by the basal leg bending back- nutation of buried and arched wards from the upper part, that is epicotyl, traced on a horizon-in a direction opposite to tho depen- tal glass, from 9.20 A.M. to 8.15 P.M. Movement of bead dent tip, in the same mo.nnor as of filament magnified 27 occurred with the hypocotyl of times. the cabbage. Another buried and arched epicotyl was observed in the same manner, excepting that the two legs of tho arch were tied together with fine silk for the sake of preventing the great movement just mentioned. It moved, however, in the evening in the same direction as before, but the line followed was not so straight. During the morning the tied arch moved in an irregularly circular, strongly zigzag course, and to a greater distance than in the previous case, as was shown in a tracing, magnified 18 times. 1lhe movements of a young plant bearing a few leaves and of a mature plant, will hereafter be described. |