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Show 16 CIRCUl\1NU'rATION OF SEEDLINGS. CHAP. I. two cotyledons parallel to the window. It was thus left the whole day so as to accommodate itself to the lig~t .. On the following morning a filament was fixed to the m1dnb of the larger and taller cotyledon (which enfolds the other a~d smaller one, whilst still within the seed), and a mark bem? placed close behind, the movement of the whole plant, t~at IS, of the hypocotyl and cotyledon, was traced greatly magmfied on a : ertical glass. At first the plant bent so much towards the hght that it was useless to attempt to trace the movement; but at 10 A.M. heliotropism almost wholly ceased and the first dot was Fig. 6. Brassica oleracea: conjoint circumnutation of the hypocotyl aml cotyl.e~o ns during 10 hours 45 minutes. l?igure here reduced to one-half ongmal scale. made on the glass. The last was made at 8.45 P.M.; seventeen dots being altogether made in this interval of 10 h. 45 m. (see Fig. 6). It should be noticed that when I looked shortly after 4 P.M. the bead was pointing off the glass, but it came on again at 5.30 P.M., and the course during this interval of 1 h. 30m. has been filled up by imagination, but cannot be far from correct. , The bead moved seven times from side to side, and thus de. scribed 3! ellipses in 10! h.; each being completed on an average in 3 h. 4 m. On the previous day another seedling had been observed under similar conditions, excepting that the plant was so CIIAP. I. BRASSICA. ]7 placed that a line joining the two cotyledons pointed towards the window; and the filament was attached to the smaller cotyledon on the side furthest from the window. Moreover the plant was now for the first time placed in this position. 'The cotyledons bowed themselves greatly towards the light from 8 to 10.50 A.M., when the first dot was made (Fig. 7). During tho Fig. 7. B,·assica oleracea: conjoint circumnutation of the hypocotyl and cotyledons, f1·om 10.50 A.M. to 8 A.M. on the following morning. Tracing mad(' on a vertical glass. next 12 hours the bead swept obliquely up and down 8 times and described 4 figures representing ellipses; so that it travelled 01t nearly the same rate as in the previous case. During the night it moved upwards, owing to the sleep-movement of the cotyledons, and continued to move in the same direction till 9 A.M. on the following morning; but this latter movement would not have occurred with seedlings under their natural conditions fully exposed to the light. By 9.25 A.M. on this second day the same cotyledon had c |
