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Show 48 CIRCUMNUrrATION OF SEiiJDLINGS. CHAP. I. 3.45 A.M. When again looked Fig. 35. 1fJ ~liO':p.:.w, .21. fpom03a ca31'ttlea : circumnutation of cotyledon, traceJ on vertical glass, from 6.10 .A..l\I, June 21st to 6.45 A.M. 22m!. Cotyleuon with petiole 1 · 6 inch in length, apex of blade 4 · 1 inch from the vertical glass ; so moYement not greatly magnified ; temp. 20° C. at, at G.lO A.M. (21st), it had fallen largely. A new tracing was now begun (see Fig. 35). and soon afterwards, at 6.4.2 A.M., the cotyledon had 1·ison a little. During the forenoon it was observed about every hour; but between 12.30 and 6 P.M. every half-hour. If tho observations had been maJe at these short intervals during the whole day, the figure would have been too intricate to have been copied. As it was, the cot.ylodon moved up and down in the course of 16 h. 20m. (i c. between 6.10 A.M. aud 10.30 P.M.) thirteen times. The cotyledons of this seedling sank downwards during both evenings and the early part of the night, but rose during the latter part. As this is an unusual movement, tho cotyledons of twelve other soocllings were observed; they stood almost or quite horizontally at mid-day, and at 10 P.M. wore all declined at various angles. The most usual angle was between 30° and 35°; but three stood at about 50° and one at even 70° beneath the horizon. The blades of all these coty lodons had attained almost their full size, viz. from 1 to U inches in length, measured along their midribs. It is a remarkable fact that whilst young-that is when loss than half an inch i~ length, measured in the same mann01·-thoy do not sink CHAP. I. CER!NTHE. ':W downwards in the evening. Therefore their weight, which i~ considerable when almost fulJy developed, probably came into play in originally determining the downward movement. Thl' periodicity of this movement is much influenced by the degree of light to which the seedlings have been exposed during the day; for three kept in an obscure place began to sink about noon, instead of late in tho evening; and those of another seedling were almost paralysed by having been similarly kept during two whole days. Tho cotyledons of several other species of Ipomcea likewise sink downwards late in the evening. Cerinthe may'or (Boraginero).-The circumnutn.tion of the bypocotyl of a young seedling with the cotyledons hardly Fig. 36. \ -I Gcrinthe major: circumnutation of hypocotyl, with filament fixed across its summit, illuminated from above, traced on horizontal glass, from 9.26. A.:M. to 9.53 l'.M. on Oct. 25th. Movement of the bead ma<rnified 30 ttmes, here reel need to one-third of original scale. "' expanded, is shown in tho annexed figure (Fig. 36), which ~pparently represents four or five irregular ellipses, describe<.t m the course of a little over 12 hours. Two older seedlino·s ~ere similarly observed, excepting thn.t one of them was ke~t I~ the dark; their hypocotyls also circumnutated, but in a more s~mpl~ manner. The cotyledons on a seedling exposed to the bght fell from the early morning until a little after noon, and then .continued to rise until 10.30 P.M. or later. The cotyledons of this same seedling acted in the same general manner durino· the two following days. It had previously been tried in th~ dark, and after being t~us ~ept for only 1 h. 40 m. the cotyledon~ beg~n at 4.30 P.M. to smk, mstead of continuing to rise till ln.te at mght. E |