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Show 20 OIUCU:M:NU'rATION OF SEEDLINGS. CHAP. I. d d as FI·g 10 here stands) being a little lengthencrl up an own, · ll b 11 or shortened; whereas any lateral movement wou .( e we . Fig. 10. B1·assica oleracea : circumnutation of a cotyledon, the hypocotyl having been secured to a stick, traced on a horizontal glass, in darkness, from 8.15 A.l\f. to 10.30 l'.J\1. Movement of the Lead of the filament magnified 13 times. exhibited. The present tracmg shows that the cotyledon did thus move later.ally (that is, from side to side in tho tracmg) 12 times in the 14 h. 15 m. of obso~vation. Therefore the cotyledons. cortmnly circumnutatod, though the chiOf m~voment was up and down in a vertical plane. Rate of movement.-The movements. of the hypocotyls and cotyledons of soodlmg cabbages of different ages 1-:avo now boon sufficiently illustrated. With respect to the rate, seedlings were placed under the microscope with the stage remove~, and with a micrometer eye-piece so adJusted that each division equalled -ge\o inch; ~he plants were illuminated by light passmg through a solution ofbichromat~ of po.tassium 80 as to eliminate heliotropism. Under these circumstances it was interesting to observe how rapidly tho circumnutating apex of a cotyledon passed acr?ss tP.e divisions of the micromo~er. Whilst travelling in any direction tho apex generally o~Cillated l.>a~~(wards and forwards to the extent of 5~o and. som?times of ncar Y _ l _ fan inch These oscillations were qmte different from the t;o~~ling cau~ed by any disturbance in the s~me roo~ or ~Y the shutting of a distant door. 'fhe first seedlmg obso1ved ~as nearly two inches in height and had been etiolated by hav~ng been grown in darkness. The tip of the cotyledon ~asse~ across 10 divisions of the micrometer, that is, 5 1 0 of an I~ch, m 6 rn~ 40 S Short glass filaments wore then fixed vertiCally to th hypo·c oty ls of several seedlings so as to proJ·e ct a !I't tl e a b ovc the cotyledons, thus exaggerating the rate of move~~nt; but onl~s~ few of the observations thus made are worth givmg. The~ remarkable fact was the oscillatory movement above dcscr~e~, d the difference of rate at which the point crossed the IVI-asino ns of the micrometer, after short m. terva1 s of t' For 1m~. instance, a tall not-etiolated seedling had been ~ept for1.14n~· in darkness; it was exposed before a north-cast wmdow fo_ o Y CnAP. I. GITHA GO. 21 two or three minutes whilst a glass filament was fixed vertically to tho hypocotyl; it was then again placed in darkness for half an hour and afterwards observed by light passing through bichromate of potassium. The point, oscillating as usual, crossed five divisions of thA micrometer (i. o. m inch) in 1m. 30 s. Tho seedling was then left in darkness for an hour, and now it required 3m. 6 s. to cross one division, that is, 15 m. 30 s. to have crossed five divisions. Another seedling, after being occasionally observed in tho back part of a northern room with a very dull light, and left in complete darkness for intervals of half an hour, crossed five divisions in 5 m. in the direction of the window, so that we concluded that tho movement was heliotropic. But this was probably not the case, for it was placed close to a north-east window and left there for 25 m., after which time, jnstead of moving still more quickly towards the light, as might have been expected, it travelled only at tho rate of 12m. 30 s. for five divisions. It was then again left in complete darkness for 1 h., and the point now travelled in the same direction as before, but at the rate of 3m. 18s. for five divisions. We shall have to recur to the cotyledons of the cabbage in a future chapter, when wo treat of their sleep-movements. The circumnutation, also, of the leaves of fully-developed plants will hereafter be described. Fig. 11. Git!tngo se,qetwn: circum nutation of hypocotyl, traced on a horizontal gla~s, by means of a Jilament Jjxed transversely across its summit from ~.15 A.M. to 12.15 P.M. on the following day. Movement of Lead of filament magnifi ed about 13 times, here reduced to one-half the original scale. Githago segetum (Caryophyllere).-A young seedling was tUmly illuminated from above, and the circumnutation of tho hypo- |