CHAP. IX. TRANSMITTED EFFECTS OF LIGHT. 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. Neverthe- 

 less, 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 9h. before a paranin 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, rather above 01 

 of an inch in width ; but they were not so sharp and regular 

 as those made by Phalaris and Avena, and therefore could not 

 be so easily measured under the microscope. The hypocotyls 

 were found, when the sand was removed on one side, to be 

 curved to a depth beneath the surface in three cases of at least 

 1 inch, in a fourth case of 11, and in a fifth of * 15 inch. The 

 chords of the arcs of the short?, buried, bowed portions formed 

 angles of between 11 and 15 with the perpendicular. From 

 what we have seen of the impermeability of this sand to light, 

 the curvature of the hypocotyls certainly extended down to a 

 depth where no light could enter; and the curvature must 

 have been caused by an influence transmitted from the upper 

 illuminated part. 



The lower halves of five young hypocotyls were surrounded by 

 unpainted gold-beaters' skin, and these, after an exposure of 8 h. 

 before a paranin lamp, all became as much bowed to the light 

 as the free seedlings. The lower halves of 10 other young 

 hypocotyls, similarly surrounded with the skin, were thickly 

 painted with Indian ink; their upper and unprotected halves 

 became well curved to the light, but their lower and protected 

 halves remained vertical in all the cases excepting one, and on 

 this the layer of paint was imperfect. This result seems to 

 prove that the influence transmitted from the upper part is 

 not sufficient to cause the lower part to bend, unless it be at 

 the same time illuminated ; but there remains the doubt, as in 



