The most successful trial on any one day (included in the above results) is worth describing in detail.  Six young seedlings were selected, the hypocotyls of which were nearly .45 inch, excepting one, which was .6 inch in height, measured from the bases of their petioles to the ground.  Their upper halves, judged as accurately as could be done by the eye, were folded once round with gold-beaters’ skin, and this was painted thickly with Indian ink.  They were exposed in an otherwise darkened room before a bright paraffin lamp, which stood on a level with the two pots containing the seedlings.  They were first looked at after an interval of 5 h. 10 m., and five of the protected hypocotyls were found quite erect, the sixth being very slightly inclined to the light; whereas all the many free seedlings in the same two pots were greatly bowed to the light.  They were again examined after a continuous exposure to the light of 20 h. 35m.; and now the contrast between the two sets was wonderfully great; for the free seedlings had their hypocotyls extended almost horizontally in the direction of the light, and were curved down to the ground; whilst those with the upper halves protected by the painted skin, but with their lower halves fully exposed to the light, still remained quite upright, with the exception of the one which retained the same slight inclination to the light which it had before.  This latter seedling was found to have been rather badly painted, for on the side facing the light the red colour of the hypocotyl could be distinguished through the paint.

We next tried nine older seedlings, the hypocotyls of which varied between 1 and 1.6 inch in height. the gold-beaters’ skin round their upper parts was painted with black grease to a depth of only .3 inch, that is, from less than a third to a fourth or fifth of their total heights.  They were exposed to the light for 7 h. 15 m.; and the result showed that the whole of the sensitive zone, which determines the curvature of the lower [page 481] part, was not protected from the action of the light; for all 9 became curved towards it, 4 of them very slightly, 3 moderately, and 2 almost as much as the unprotected seedlings.  Nevertheless, the whole 9 taken together differed plainly in their degree of curvature from the many free seedlings, and from some which were wrapped in unpainted skin, growing in the same two pots.

Seeds were covered with about a quarter of an inch of the fine sand described under Phalaris; and when the hypocotyls had grown to a height of between .4 and .55 inch, they were exposed during 9 h. before a paraffin lamp, their bases being at first closely surrounded by the damp sand.  They all became bowed down to the ground, so that their upper parts lay near to and almost parallel to the surface of the soil.  On the side of the light their bases were in close contact with the sand, which was here a very little heaped up; on the opposite or shaded side there were open, crescentic cracks or furrows,