96 CORAL AND ATOLLS 



The vegetative habit of a coral, as we have seen, is no true 

 index of its species. Its method of asexual reproduction, the 

 characters of its corallites and surface structure, and also its 

 coloration, are equally variable. 



Coloration depends on many, and very little understood, 

 influences. Corals from deeper waters lose their pigment ; 



Fig. 29. Fig. 30. 



Diagram of Type op Growth Diagram op Growth op 



OF Madrepora Madrej^ora pulchra 



When living in water free of When living in a habitat exposed to 



sediment, {M.pidclira.) the action of sediment. 



and corals that are struggling hard in adverse circumstances — 

 corals in fact that are about to die — become highly pigmented. 

 Corals identical in every other respect, and living side by 

 side, may be differently coloured. Nothing is more familiar 

 than the purple, brown, yellow, or greenish Porites masses which 

 live under exactly the same conditions, as far as can be 

 determined. Even one colony may be differently coloured in 

 different parts. In Pocillopora there is a dimorphism of 

 coloration, some growths being pink and some pale brown : 

 the pink is a very beautiful and striking colour, and yet the 

 corals are identical when dead, and the zooid in both cases is 



