314 COLOUR IN NATURE chap. 



that lipochromes are of great importance both as 

 reserve stuffs and as oxygen carriers in the process 

 of assimilation. When the metabolism of the cell is 

 active, oxygen is withdrawn from the yellow pigment, 

 and it becomes converted into green chlorophyll. 

 When metabolism diminishes, the green chlorophyll 

 becomes oxidised and is converted into a lipochrome, 

 and thus the colours of autumnal leaves, of fruits, and 

 of flowers are produced. The fact that chlorophyll 

 is commonly regarded as a nitrogenous compound, 

 which the lipochromes are certainly not, is nowhere 

 alluded to. Lipochromes, Simroth regards as pig- 

 ments of relatively great simplicity, especially char- 

 acteristic of plants as the simpler organisms. When 

 they occur in animals, they are to be looked upon 

 as evidences of a primitive condition, though they 

 may be utilised for purposes of warning coloration, 

 mimicry, etc., such colours, according to the author, 

 being always of simple nature. If lipochromes are, 

 however, evidences of a primitive condition, it is 

 difficult to understand why they should be so frequent 

 in birds ; but the author does not touch upon this. 



The third kind of evidence upon which Simroth 

 bases his thesis is the order of appearance of the 

 colours which either belong to the right half of the 

 spectrum, or are not pigmental colours at all. Such 

 pigments are characterised by their chemical com- 

 plexity, and are associated with complex tissues. 

 Thus the greater intensity of animal life expresses 

 itself in the nature of animal pigments ; the masses 

 of simple colours, like red, yellow, and green, which 

 are so common in plants, being rare in animals (but 

 Crustacea ?). 



