472 TRANSMITTED EFFECTS OF LIGHT CHAP. IX. 



tubes ; and these were then exposed before a south-west window 

 on a bright day for 8 h. All of them became strongly curved 

 towards the light, in the same degree as the many other free 

 seedlings in the same pots ; so that the glass-tubes certainly did 

 not prevent the cotyledons from bending towards the light. 

 Nineteen other cotyledons were, at the same time, similarly 

 enclosed in tubes thickly painted with Indian ink. On five of 

 them, the paint, to our surprise, contracted after exposure 

 to the sunlight, and very narrow cracks were formed, through 

 which a little light entered ; and these five cases were rejected. 

 Of the remaining 14 cotyledons, the lower halves of which had 

 been fully exposed to the light for the whole time, 7 continued 

 quite straight and upright ; 1 was considerably bowed to the 

 light, and 6 were slightly bowed, but with the exposed bases of 

 most of them almost or quite straight. It is possible that some 

 light may have been reflected upwards from the soil and entered 

 the bases of these 7 tubes, as the sun shone brightly, though 

 bits of blackened paper had been placed on the soil round 

 them. Nevertheless, the 7 cotyledons which were slightly 

 bowed, together with the 7 upright ones, presented a most re- 

 markable contrast in appearance with the many other seedlings 

 in the same pots to which nothing had been done. The 

 blackened tubes were then removed from 10 of these seedlings, 

 and they were now exposed before a lamp for 8 h. : 9 of them 

 became greatly, and 1 moderately, curved towards the light, 

 proving that the previous absence of any curvature in the 

 basal part, or the presence of only a slight degree of curvature 

 there, was due to the exclusion of light from the upper part. 



Similar observations were made on 12 younger cotyledons 

 with their upper halves enclosed within glass-tubes coated with 

 black varnish, and with their lower halves fully exposed to 

 bright sunshine. In these younger seedlings the sensitive zone 

 seems to extend rather lower down, as was observed on some 

 other occasions, for two became almost as much curved towards 

 the light as the free seedlings; and the remaining ten were 

 slightly curved, although the basal part of several of them, 

 which normally becomes more curved than any other part, 

 exhibited hardly a trace of curvature. These 12 seedlings 

 taken together differed greatly in their degree of curvature from 

 all the many other seedlings in the same pots. 



Better evidence of the efficiency of the blackened tubes was 

 incidentally afforded by some experiments hereafter to be given, 



