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Show 38 CIROUMNUTATION OF SEEDT-'INGS. CHAP. I. move both up and down and laterally; but they do not rise Ul) at night in a conspicuous manner. . . Lttpimts Zuteus (Leguminosre).-SeedlJDO'~ of th1s plnnt were observed because the cotyledons are so thick (about ·OS of an inch) that it seemed unlikely that they would mov?. Our observations were not very E>uccessful, as tl1o seedln1o·s arc strongly heliotropic, and their circumm~tation could not be accurately observed near a north-cast w1_ndow, although YlCY had been kept during tho previous day m the same pos1t10n. A seedling was then placed in darkness with the bypocotyl secured to a stick; both cotyledons rose a little at first, and then fell durin()' the rest of tho day; in the evening between 5 and 6 P.M. they moved very slowly; during tho 11ight one continued to fall and the other rose, though only a little. The tracing was not much magnified, and as the lines were plainly zigzag, the cotyledons must have moved a little laterally, that is, they must have circumnutatecl. . The hypocotyl is rather thick, about ·12 of mch; nevertheless it circumnutatecl in a complex course, though to a small extent. The movement of an old seedling with two true loaves partially developed, was observed in the clark. As the movement was magnified about 100 times it is not trustworthy and is not given; but there could be no doubt that tho hypocotyl m_ovecl in all directions during the day, changing its course 19 t1mcs. Tho extreme actual distance from side to side through ·which the upper part of the hypocotyl passed in the course of 14~ hours was only an of an inch; it sometimes travelled at the rate of -r}o of an inch in an hour. Cucu1·bita ovifera (Cucurbitacere).-Radicle: a seed which had Fig. 26. ....... -----------------"-·-----.. --------·~~ - ..~ Oucurbitn ov•fera: course followed hy a radicle in bending geotropi cal~~ downwards, traced on a horizontal glass, between 11.2.) A.Jil . and 10 .• J l'.M.; the direction during the night is indicated Ly the broken lJllc. Movement of bead magnified 14 times. germinated on damp sand was fixed so that the slightly cuned 1·adicle, which was only ·07 inch in length, stood almost vertically CHAP. I. CUOURBITA. 39 upwards, in which position geotropism would act at first with little power. A filament was attached near to its base, and pL'ojectod at about an angle of 45° above the horizon. Tho general course followed during the 11 hours of observation and during the following night, is shown in tho accompanying diagram (Fig. 26), and was plainly due to geotropism; but it was also clear that the radicle circumnutated. By the next moming the tip had curved so much downwards that the :filame~ t, instead of projecting at 45° above tho horizon, was nearly honzontal. Another germinating seed was turned upside clown and covered with damp sand; and a filament was fastened to tho radicle so as to project at an angle of about 50° above tho horizon; this radicle was · 35 of an inch in lono-th and a little curved. Tho course pursued was mainly govo~1ed, as in the last case, by geotropism, but tho line traced durinO' 12 hours and magnified as bef0re was more strongly zigzag, ~gain showing circumnutation. Four radicles were allowed to grow downwards over plates of smoked glass, inclined at 70° to tho horizon, unde~ the Fig. 27. A. B. Oucnrbita ovifera : tracks left by tips of raclicles in growing downwards over smoked glassplates, inclined at 70° to the horizon, Fig. 28. Oucu~·bita ovifera: circumnutation of arched hypocotyl at a very early age, traced in darkness on a horizontal glass, from 8 A.l\1. to 10.20 A.llr. on the following day. The movement of the bead magnified 20 times, here reduced to onehalf of original scale . samo conditions as in the cases of lEsculus, Phascolus, and Vicia. Facsimiles arc here given (Fig. 27) of two of these tracks; and a third short one was almost as plainly serpentine as that at A. It was also manifest by a greater or less amount of soot having been swept off the glas~es, that the tips had |