1873-] Comparative Vegetable Chromatology. 459 



comparative quantitative analyses, I subjoin the following 

 table. It would have been of very little use to have com- 

 pared equal weights of different plants, since the amount 

 of endochrome is so very different, and it is the variation in 

 its composition that is of chief interest. It was therefore 

 necessary to assume some one constituent equal in all cases, 

 and the only one suitable for this purpose was the blue 

 chlorophyll. This, then, was taken at 100 in all the 

 specimens, and the relative amount of the other constituents 

 calculated accordingly, 100 being taken as the maximum 

 quantity for each kind of colouring matter. By adopting 

 this plan, of course the amount of some of the constituents 

 is made to appear as though it were increased by greater 

 exposure to light, in the same order as they are less and less 

 decomposed by its action ; but in reality the amount is 

 diminished in the opposite order, as would be made apparent 

 by assuming as equal the constituent least changed by light, 

 or by taking an equal weight of the different specimens of 

 each separate kind of plant. 



1 2 o j*S • 5§ S -55 



1 o ^° oc o ns 



Fucus grown in the shade ioo go o 3 77 11 



,, ,. sun 100 100 o 3^ 100 14 



OscillatoricB under water ) ,„„ „„ 



, 1 1 \ 100 13 o 1 51 6 



in a very shady place j J D 



OscillatoricB in more light 100 19 36 3 55 10 



OscillatoricB in and on ] 



water, exposed to the Y 100 trace 67 25 11 9 



sun j 



Oscillatoria on a dampj 



wall quite open to the L 100 trace 100 77 25 23 



sun and air j 



Peltieera in a medium | T ^ *„.„« 



amount of light.. ..} I0 ° trace 2 ? 3 2 ° 32 



>eltigera exposed ,toj m trace ^ IOQ Q ^ 



much sun 



On comparing the relative quantities of the different 

 substances, it will be seen that, as before named, very great 

 changes are due to the difference in the amount of light, 

 some of which may be referred to its direct decomposing 

 action, and others to its indirect; influence on the con- 

 structive energy of the plant. The most important 

 general fact, however, is that, when the OscillatoricB grow 

 in a very feeble light, the phycoxanthine and orange xantho- 

 phyll almost or quite disappear, whilst the amount of fuco- 

 xanthine increases, so that the general relation of the 

 colouring matters approaches that of the Fucus; whereas, 



