OAK. 187 



chemical reactions; they are differently affected 

 by light; and they give distinct spectra. Mr. 

 Sorby further states that scores of different colour- 

 ing 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 enquiries 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 intro- 

 duce 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 pig- 

 ments to light, the changes they undergo during 



M 



