LOSS OF COLOUR 157 



the one red, the other green, appear as cousins, related 

 through some as yet undiscovered stock. Each has 

 diverged at some remote epoch along a line of its own, 

 and in course of time produced the substance that 

 we know as the green colouring matter of plants and 

 the red pigment of the blood of animals. 



Yet, in spite of this divergence and seeming dis- 

 parity, we can detect points not only of resemblance, 

 but of affinity. Both have a like, though hidden, 

 family constitution, indicative of a common but 

 remote genetic connection. They occur with un- 

 failing regularity in the higher divisions of the two 

 kingdoms of living nature, and become less constant 

 in the lower members of animal and plant life. In 

 those plants which live parasitically upon the tissues 

 of other organisms the green colouring matter is absent. 

 Its nutritive power of making and purveying sugar, 

 starch, or oil is not required. 



In the vast class of moulds, mushrooms, and toad- 

 stools there is not one that has the requisite green 

 pigment. Amongst typically green plants there are 

 still more striking examples of the loss of colour 

 following upon the adoption of parasitic habits. 



The dodder that infests vetches and clover sucks 

 the juices of its host and loses its livery. The minute 

 colourless Flagellata which abound in organic infusions 

 are cousins to those Euglence that fill the roadside 

 hollows with a green scum, and if only water and light 

 are supplied to them their colourless bodies reassume 

 the green tint and create a food store from such 



