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Show 480 TRANSMITTED EFFECTS OF LlGli'r . CnAI'.lX. exceptions, for on removing tho skin tl10 paint was found imperf ct and was penetrated by many small trn.nsp::trent spaces on tho side which faced the light. 1\fol'cover,. in two other cases the painted skin din not extend quite haUway clown the hypocotyl. Altogether there was a woJtd erf'ul contrast in tho several pots between these 20 hypocotyls and tho other many free seedlings, which were all greatly bowed down to their bases in the direction of tho light, some bein g 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 seedlings were selecton, tho hypocotyls of which were nearly ·4.5 inch, excepting one, which was · 6 inch in height, measured from tbe bases of their petioles to the ground. 'rhoir upper halves, judged as accnratoly as could be dmw by the eye, were folded ouce round with gold-beater s' skin, aml this was painted thickly with Indian ink. They were exposed in an otherwise darkened room before a bright par:1ffin lamp, which stood on a level with the two pots containing tho seedlings. They were first looked at after ao interval of G lt. 10 m., ancl fi~e of the protected hypocotyls were found qnitc 01·ect, the . ixtl1 being very slightly inclined to tho light ; whereas all the many free soedlino·s in tho same two pots were greatly bowed b . to the light. They wore rtgain examined after a contmuous exposure to the light of 20 h. 3G m.; and now the contra I between the two sets was wonderfully groat; for the free seedlings had their hypocotyls extended almost horizontally in the direction of the light, and wer e curved down to the gro~ncl ; whilst those with the upper halves protected by th~ pamt~d skin, but with their lower halves fully exposed to the l1ght, s~ll remained quite upright, with the exception of tbe ?ne _whJCh retained the same slight inclination to t ho light whJCh 1t had before. This latter seedling was fouml to ha-ve been rather badly painted, for on the side facing tho light the re~ colour of the hypocotyl could be distinguished through the pamt. . We next tried nino older seedlings, the hypocotyls of which varied between 1 and 1· 6 inch in height. The gold-beaters' skin round their upper parts was pain ted with black grease to . h' ·d t fourth a depth of only · 3 inch, that 1s, from less than a t u 0 a . ht or fifth of their total heights. They were exposed to the :~~b for 7 h 15 m · and the result showed that the whole 0 e · · ' . . . t . f the lower sensitive zone, which determmcs the cmva me 0 CHAP. IX. TRANSMITTED EFFEO'rS OF LIOII'r. 4 1 part, was not protected _from tho action of the light; for nil 9 became curved townrcls 1t, 4 of thorn very slightly, 3 moclcrately, and 2 almost as much as the uni rotcctocl seedlings. Novortheless, the whole 9 taken together differed plainly in their cleo-roe of curvature from the many free sccdlino·s, and from s~mo which were wrapped in unpainted skin, growing in the same two pots. Seeds were covered with about a quarter of an inch of the fino sand described under Phalnris ; and when tho hypocotyls hatl grown to a height of }Jet ween · 4 and ·55 inch, they were expo eel during 9 h. before a paraffin lamp, their bases being at first closely surrounded by the damp sand. They nil became bow ·cl down to the ground, so that their upper parts ln.y near to aml almost parallel to the surface of tho soil. On the side of tho light their bases wore in close contact with tho 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 A vena, and therefore could not be so easily measured under the microscope. The hypocoty ls were found, when the sand was removed on ono side to be curved to a depth beneath the smfaco in three cases of ~t 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 clown to n. depth where no light could enter; and tho curvature must have been camed 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 paraffin lamp, all became as much bowed to the light ns the free seedlings. 'rhe 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 ha._lves remained vertical in all tho 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 tho doubt, as in ') T |