thus so much obscured that, judging by the unassisted eye, the seedlings appeared to receive more light from the interior of the room than from the window; but this was not really the case, as was shown by a very faint shadow cast by a pencil on a card.  Nevertheless, this extremely small excess of light on one side caused the hypocotyls, which in the morning had stood upright, to bend at right angles towards the window, so that in the evening (after 4.23 P.M.) their course had to be traced on a vertical glass parallel to the window.  It should be stated that at 3.30 P.M., by which time the sky had become darker, the towel was removed and replaced by an additional muslin blind, which itself was removed at 4 P.M., the other two [page 426] blinds being left suspended.  In Fig. 173 the course pursued, between 8.9 A.M. and 7.10 P.M., by one of the hypocotyls thus

Fig. 173.  Brassica oleracea:  heliotropic movement and circumnutation of a hypocotyl towards a very dim lateral light, traced during 11 hours, on a horizontal glass in the morning, and on a vertical glass in the evening.  Figure reduced to one-third of the original scale.

exposed is shown.  It may be observed that during the first 16 m. the hypocotyl moved obliquely from the light, and this, [page 427] no doubt, was due to its then circumnutating in this direction.  Similar cases were repeatedly observed, and a dim light rarely or never produced any effect until from a quarter to three-quarters of an hour had elapsed.  After 5.15 P.M., by which time the light had become obscure, the hypocotyl began to circumnutate about the same spot.  The contrast between the two figures (172 and 173) would have been more striking, if they had been originally drawn on the same scale, and had been equally reduced.  But the movements shown in Fig. 172 were at first more magnified, and have been reduced to only one-half of the original scale; whereas those in Fig. 173 were at first less magnified, and have been reduced to a one-third scale.  A tracing made at the same time with the last of the movements of a second hypocotyl, presented a closely analogous appearance; but it did not bend quite so much towards the light, and it circumnutated rather more plainly.

Fig. 174.  Phalaris Canariensis:  heliotropic movement and circumnutation of a rather old cotyledon, towards a dull lateral light, traced on a horizontal glass from 8.15 A.M.  Sept. 16th to 7.45 A.M. 17th.  Figure reduced to one-third of original scale.

Phalaris Canariensis.—­The sheath-like cotyledons of this monocotyledonous plant were selected for trial, because they are very sensitive to light and circumnutate well, as formerly shown (see Fig. 49, p. 63).  Although we felt no doubt about the result, some seedlings were first placed before a south-west window on a moderately bright morning, and the movements of one were traced.  As is so common, it moved [page 428] for the first 45 m. in a zigzag line; it then