480 TRANSMITTED EFFECTS OF LIGHT. CHAP. IX. 



exceptions, for on removing the skin the paint was found im- 

 perfect and was penetrated by many small transparent spaces 

 on the side which faced the light. Moreover, in two other cases 

 the painted skin did not extend quite halfway down the hypo- 

 cotyl. Altogether there was a wonderful contrast in the several 

 pots between these 20 hypocotvls and the other many free 

 seedlings, which were all greatly bowed down to their bases in 

 the direction of the light, some being almost prostrate on the 

 ground. 



The most successful trial on any one day (included in the 

 above results) is worth describing in detail. Six young seed- 

 lings 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 paintec! 

 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 hypocotyla 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. 35 m. ; and now the contrast 

 between the two sets was wonderfully great : for- the free seed- 

 lings 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 



