222 TKOPICAL NATUUE, AND OTHER ESSAYS. 



differently affected by light; and they give distinct 

 spectra. Mr. Sorby further states that scores of different 

 colouring matters are found in the leaves and flowers of 

 plants, to some of which appropriate names have been 

 given, as erythrophyll which is red, and phaiophyll 

 which is brown ; and many of these differ greatly from 

 each other in their chemical composition. These in- 

 quiries are at present in their infancy, but as the original 

 term chlorophyll seems scarcely applicable under the 

 present aspect of the subject, it would perhaps be better 

 to introduce the analogous word Chromophyll, as a 

 general term for the colouring matters of the vegetable 

 kingdom. 



Light has a much more decided action on plants than 

 on animals. The green colour of leaves is almost wholly 

 dependent on it ; and although some flowers will become 

 fully coloured in the dark, others are decidedly affected 

 by the absence of light, even when the foliage is fully 

 exposed to it. Looking therefore at the numerous 

 colouring matters which are developed in the tissues 

 of plants, the sensitiveness of these pigments to light, 

 the changes they undergo during growth and develop- 

 ment, and the facility with which new chemical com- 

 binations are effected by the physiological processes of 

 plants as shown by the endless variety in the chemical 

 constitution of vegetable products, we have no difliculty 

 in comprehending the general causes which aid in pro- 

 ducing the colours of the vegetable world, or the extreme 

 variability of those colours. We may therefore here 

 confine ourselves to an inquiry into the various uses of 

 colour in the economy of plants ; and this will generally 

 enable us to understand how it has become fixed and 



