We shall have to recur to the cotyledons of the cabbage in a future chapter, when we treat of their sleep-movements.  The circumnutation, also, of the leaves of fully-developed plants will hereafter be described.

Fig. 11.  Githago segetum:  circumnutation of hypocotyl, traced on a horizontal glass, by means of a filament fixed transversely across its summit, from 8.15 A.M. to 12.15 P.M. on the following day.  Movement of bead of filament magnified about 13 times, here reduced to one-half the original scale.

Githago segetum (Caryophylleae).—­A young seedling was dimly illuminated from above, and the circumnutation of the hypo-[page 22] cotyl was observed during 28 h., as shown in Fig. 11.  It moved in all directions; the lines from right and to left in the figure being parallel to the blades of the cotyledons.  The actual distance travelled from side to side by the summit of the hypocotyl was about .2 of an inch; but it was impossible to be accurate on this head, as the more obliquely the plant was viewed, after it had moved for some time, the more the distances were exaggerated.

We endeavoured to observe the circumnutation of the cotyledons, but as they close together unless kept exposed to a moderately bright light, and as the hypocotyl is extremely heliotropic, the necessary arrangements were too troublesome.  We shall recur to the nocturnal or sleep-movements of the cotyledons in a future chapter.

Fig. 12.  Gossypium:  circumnutation of hypocotyl, traced on a horizontal glass, from 10.30 A.M. to 9.30 A.M. on following morning, by means of a filament fixed across its summit.  Movement of bead of filament magnified about twice; seedling illuminated from above.

Gossypium (var.  Nankin cotton) (Malvaceae).—­The circumnutation of a hypocotyl was observed in the hot-house, but the movement was so much exaggerated that the bead twice passed for a time out of view.  It was, however, manifest that two somewhat irregular ellipses were nearly completed in 9 h.  Another seedling, 1 ½ in. in height, was then observed during 23 h.; but the observations were not made at sufficiently short intervals, as shown by the few dots in Fig. 12, and the tracing was not now sufficiently enlarged.  Nevertheless there could be no doubt about the circumnutation of the hypocotyl, which described in 12 h. a figure representing three irregular ellipses of unequal sizes.

The cotyledons are in constant movement up and down during the whole day, and as they offer the unusual case of moving downwards late in the evening and in the early part of the night, many observations were made on them.  A filament was fixed along the middle of one, and its movement traced on a vertical glass; but the tracing is not given, as the hypocotyl was not secured, so that it was impossible to distinguish clearly between its movement and that of the cotyledon.  The cotyledons rose from 10.30 A.M. to about 3 P.M.; they then sank till 10 P.M., rising, however, greatly in the latter part of the night. [page 23] The angles above the horizon at which the cotyledons of another seedling stood at different hours is recorded in the following short table:  —­