84 CORAL AND ATOLLS 



case ; and tliougli, after long familiarity with living corals, 

 one may feel certain tliat two entirely different vegetative 

 forms belong to the same species, yet the conclusive proof 

 may be lacking. 



Collecting very extensive series of variations will, in some 

 cases no doubt, link up extremely diverse forms, and study- 

 ing the repair of damaged specimens will serve to make others 

 clear ; but experimental breeding, and the rearing of identical 

 species in diverse surroundings, must be the final test in most 

 cases. Now this is a work of extreme difficulty, for an adult 

 colony, when removed from its own environment and placed 

 in a different one, almost invariably dies, and the artificial 

 rearing of corals is very troublesome ; my experience of corals 

 in aquaria is that it is very difficult even to keep them alive. 



The only method that is open to every resident in places 

 where corals flourish, and the one that I followed in the 

 Cocos-Keeling atoll, is the careful noting of every modification 

 of colonies the life-surroundings of which differ by reason of 

 some influence that can be easily recognised. By this I mean 

 that the corals of deep water and shallow water should be 

 compared ; those living in the surf and those living in calm 

 spots should be noted ; and the corals living exposed to 

 sediment should be contrasted with those living where no 

 sediment is being deposited. 



These are extremes of habitat, and at first the corals of 

 two entirely different environments will seem to be quite 

 distinct, but every compromise of conditions will be found in 

 different spots in an atoll, and with every grade of altered 

 surroundings it will soon be seen that there is a modification 

 of coral growth ; and the more completely this method of 

 observation is carried out, the more will the types of extremely 

 different habitats be found to be linked up by intermediate 

 forms. It will be best to study the influence of the different 

 conditions of life-surroundings on the form of vegetative 

 growth by taking the different possible modifications of 

 environment in order ; but first some general growth 

 tendencies of all corals must be made clear. 



