470 



Mr. H. C. Sorby on 



[June 19, 



ence in the general colour of the young leaves. I selected for com- 

 parative analysis leaves nearly a year old, representing a fair average of 

 those on the outside and in the interior, and, by methods similar to those 

 already described, I separated the colouring-matters into the mixed blue 

 and 3 r ello\v chlorophyll, orange xanthophyll, and the mixed xanthophyll, 

 yellow xanthophyll, and hchnoxanthine, and obtained the following 

 results : — 



Chlorophylls. 



Orange Mixed 

 xanthophyll. xanthophylls &c. 



In the shade 100 100 100 



In the sun 31 90 100 



I must here explain that in this and similar analyses the numbers in 

 each column have no connexion with those in the other columns. For 

 example, the 100 parts of chlorophyll have no relation to the 100 parts 

 of xanthophyll ; they do not indicate equal weights or equality in any 

 other respect. If it were desirable to compare them together, it should, 

 I think, not be by weight, but according to the total quantity of light 

 which they absorb. I take 100 to express the maximum for each colour- 

 ing-matter, and calculate out the relative amount of the same substance 

 in the other specimen accordingly — that is to say, in this case the amount 

 of chlorophyll in the leaves exposed to the sun is only 31 per cent, of 

 that in those grown in the shade. The orange xanthophyll is in a similar 

 manner reduced to 90 per cent., whereas the mixed xanthophylls &c. are 

 as nearly the same in both as could be ascertained. This great reduction 

 in the quantity of chlorophyll in the leaves exposed to the sun corre- 

 sponds of course to the increase found in the case of the one covered up 

 and protected from the light, but due to the permanent and normal 

 difference in the amount of exposure to light of different parts of the 

 plant. The effect of this in the case of Acuta is unusually great, and 

 apparent at once on comparing the leaves ; but I found that there was an 

 analogous difference in the leaves of a deep green common holly {Ilex 

 aquifolium), though it would scarcely have been noticed without special 

 examination. I found the relative quantities to be as follows : — 



Chlorophylls. J^ ylL mt h^h£ls &c 



In the shade 100 100 100 



In the sun 62 86 94 



In the case of a lichen (Platysma glaucum) I found : — 



Chlorophylls. Xanthophylls. 



In the shade 100 100 100 



In the sun 75 77 100 



In this case I did not compare equal weights of the fronds, but calcu- 

 lated out the results of the anatyses on the supposition that the amount 

 of the lichnoxanthines was the same in both. 



