CHAPTER II 



THE PIGMENTS OF ORGANISMS 



Natural and Artificial Pigments — Classification of Pigments — 

 Pigments of Direct Physiological Importance — Derived 

 Pigments — Waste Products — Reserve Products — Intro- 

 duced Pigments — Distribution of Pigmental Colours — 

 Spectroscopic Characters of Pigments. 



Although, as we have seen, some of the most 

 beautiful colours of organisms are optical effects, or 

 are produced by a combination of a pigment and a 

 certain structure, yet the vast majority of the colours 

 of plants, and the colours of many animals, owe their 

 origin to pigments only. Before proceeding to con- 

 sider the colours of the separate groups of animals 

 and plants, we shall look for a little at pigments in 

 general. 



The pigments or colouring- matters which are 

 most familiar to artists and those engaged in the 

 industries, are very frequently either artificial organic 

 substances, such as the now familiar aniline dyes, 

 or are inorganic compounds of the metals, such as 

 ultramarine and Scheele's green. Some, however, 

 of the natural organic pigments are used in the arts. 

 As is well known, the ancients obtained their Tyrian 



