18/3.] 



Comparative Vegetable Chromatology. 



481 



solution had to be diluted in order to obtain that equality. This being 

 a constant point of comparison, it is possible to determine the relative 

 quantity of yellow chlorophyll in different kinds of leaves. So far I 

 have not worked out the question in full detail, because the present form 

 of instrument and apparatus is not suited for very accurate determinations, 

 and therefore the following Table must be looked upon as a mere first 

 attempt. Great care must be taken not to expose such dilute solutions 

 to much light, since they are so rapidly changed, even by gaslight, that 

 serious errors might easily result from this cause. In all cases I have 

 taken the amount of blue chlorophyll as 100, and expressed the relative 

 quantity of }' _ ellow chlorophyll in percentages, in accordance with the 

 above named principle. I also give some other cases for comparison. 



Blue Yellow 

 chlorophyll, chlorophyll. 



Olive and red Algce 100 



Leaves grown nearly in the dark 100 5 or 6 



Normally yellow leaves grown in the light . . 100 5 or 6 



Healthy green leaves 100 13 to 17 



Green leaves faded to yellow 100 25 or 30 



Final equilibrium in solutions exposed to the 1 j_Q0 near 100 



sun J 



The normal relative amount of yellow chlorophyll in green leaves 

 certainly varies, and there seems reason to believe that this to some 

 extent, if not mainly, depends on the length of time to which they have 

 been exposed to the sun. When healthy green leaves fade and turn 

 yellow the relative amount of yellow chlorophyll is increased, in accord- 

 ance with what is known respecting the greater ease with which blue 

 chlorophyll is decomposed, but the relative amount does not appear to 

 become so great as in the case of a mixed solution exposed to the sun. 

 On the contrary, when leaves are very yellow, owing to having been 

 grown almost in the dark, the relative amount of yellow chlorophyll is 

 much less than normal, as though under such unfavourable conditions 

 the blue chlorophyll were more readily formed than the yellow. It might 

 therefore be said that when the constructive energy is weak, the initial 

 proportion of the yellow is about one third of the normal, but that when 

 the leaves fade, the vanishing ratio is about double the normal. The blue 

 chlorophyll is therefore, as it were, more readily formed and more readily 

 decomposed than the yellow. The relatively small amount of yellow chloro- 

 phyll found in those leaves which are normally very yellow cannot there- 

 fore be due to the decomposing effect of light, but must rather be attributed 

 to weak constructive energy, like that in leaves abnormally yellow on 

 account of having been grown almost in the dark. This great reduction in 

 the relative quantity of yellow chlorophyll causes them to approach 

 towards the normal type of those low orders of plants from which it is 

 altogether absent. The determination of the relative amounts of the two 



