102 



sorby's researches on chromatology. 



the relative amount of the various substances by the following 



signs : — 



A relatively large quantity * 



A relatively moderate quantity -j- 



A relatively small quantity 



Blue chlorophyll 



Yellow chlorophyll , 



Chlorofucine 



Orange xanthophyll 



Xanthophyll 



Yellow xanthophyll 



Fucoxanthine ^ 



Lichnoxanthines 



Phycocyan 



Pink phycocyan 



Eed phycoerythrine 



On inspecting this table it will be seen that the olive Algce are 

 characterized by the relatively large amount of chlorofucine and fucox- 

 anthine, and the total absence of yellow chlorophyll, of xanthophyll, 

 and of yellow xanthophyll. The red are especially distinguished by 

 the colouring matters of the phycocyan and phycoerythrine groups, 

 but also differ from the olive in containing xanthophyll and very 

 little chlorofucine and fucoxanthine. The green are characterized 

 by the presence of yellow chlorophyll and yellow xanthophyll, as 

 well as by the absence of chlorofucine, fucoxanthine, and the sub- 

 stances soluble in water, so characteristic of the red group. Blue 

 chlorophyll, orange xanthophyll, and the lichnoxanthines are com- 

 mon to all. It will also be seen that the red group is intermediate 

 between the olive and the green, and, independent of the red 

 colouring-matters, it differs from each of the other groups far less 

 than they do from one another. It is also still more closely con- 

 nected with each by other examples. My endeavour has been to 

 extend such a method of comparison to all the leading classes of 

 plants and to some of the lower classes of animals, and to ascer- 

 tain the order in which they should be arranged, so as, in like 

 manner, to show the most gradual and unbroken passage from one 

 to the other. ' 



Connexion between the loivest classes of Animals and Plants. 



Comparing these various groups of Alga? with other classes of 

 plants, and with such low classes of animals as Actinice, I found 

 that the whole of the colouring -matters present in green Alga are 

 those most characteristic of all the higher plants, the only difference 

 being that in certain circumstances these latter contain in addition 

 various more or less accidental and unessential substances, belong- 

 ing to the erythrophyll and chrysotannin groups, some kinds of 



