460 Comparative Vegetable Chromatology. [October, 



when they grow in bright light, the amount of fucoxanthine 

 is much decreased, and that of the lichnoxanthine con- 

 siderably increased, whilst the phycoxanthine and orange 

 xanthophyll are developed to a remarkable extent, so that 

 the general type approaches that of such lichens asPeltigera. 



There is also a well-marked tendency to approximate to 

 a lower type of colouring in the case of those permanent 

 varieties of plants which have very yellow leaves, on account 

 of the amount of chlorophyll being abnormally small. The 

 green leaves of the higher classes of plants contain two 

 different kinds of chlorophyll, which give quite different 

 spectra, and differ in various other important particulars. 

 These I have named blue chlorophyll and yellow chlorophyll, 

 from the difference in their general colour. Now the small 

 quantity of chlorophyll which exists in the above-named 

 leaves contains only about one-third the relative amount 

 of the yellow chlorophyll, which corresponds to what is met 

 with in leaves abnormally yellow from being grown almost 

 in the dark, as if both were due to low constructive energy, 

 one natural to the variety, and the other produced artificially. 

 Both differ greatly from green leaves which have turned yellow 

 by fading, for these contain double the normal relative amount 

 of yellow chlorophyll, which is not so readily formed, but, 

 when it has been formed, is not so readily decomposed as 

 blue chorophyll. This reduction in the relative quantity of 

 yellow chlorophyll causes leaves abnormally yellow, owing 

 to low constructive energy, to approach to the type of red 

 Algce, in which this energy is so low that blue chlorophyll 

 is developed alone, and yellow chlorophyll is quite absent. 

 If further research should prove the existence of other 

 examples of this kind of fact, and establish it as a 

 general law that when the healthy development of the higher 

 classes of plants is arrested the type of colouring ap- 

 proaches to that of lower classes, it will be very instructive 

 in connection with the theory of evolution, and analogous 

 to what is so common in the general structure of animals, 

 in which when their development is arrested it often 

 approximates more or less to that of those of lower orga- 

 nisation. It would also indicate that in some way or other 

 the constructive energy of the lowest classes of plants is 

 lower in the scale than that of the highest, but it does not 

 follow that plants with this higher type of constructive 

 energy could live in more variable and adverse conditions 

 than those with a lower type. 



It would be impossible to select a better example of the 

 manner in which different groups of plants are related, and 



