THE BIOLOGY OF THE FUNAFUTI ATOLL AND REEF FORiMATION. 147 



every animal and plant, has a limit to its growth, that is, as far as the individual corallum 

 is concerned. Thus Pocillopora grandis, the species on which such rapid growth 

 was observed, was never met with much above 12 inches in diameter. So that the 

 rate of growth determined seems merely to indicate the time required for the 

 attainment of what may be termed the adult size. 



In the preceding pages an attempt has been made to show that corals are 

 not active reef builders. A coral, once established, adds to the coral island 

 by its growth only in the same way as a tree, once established, adds by its 

 growth to the extent of a forest. The growth of the coral island cannot be 

 estimated by the rate of growth of the individual corallum, for, unless a coral, 

 no matter of what dimensions, be used by the Lithoth amnion as a foundation 

 for its growth and be cemented by it to neighbouring corals, &c., it cannot 

 enter as a whole into the formation of the reef rock of the island, although 

 what is left of its fragments after its general decay may help to form the non- 

 consolidated dry land. On the other hand, if a corallum be taken possession of by 

 the lAtliothamnion , which will cause every interstice, as well as every space between 

 the branches, if present, to be transformed into one solid mass, it will be the initial 

 cause of a solid addition to the coral island, to the extent of its bulk at the time 

 when the Lithothamnion had succeeded in over-growing it. And this bulk will 

 depend entirely on the age of the coral when overgrown, since in the young state 

 it will be small, in the older, larger. 



Considering that it has been proved that the growth of the coral is so much 

 more rapid than that of the Lithothamnion, the question may be put. What is there 

 to prevent any corallum from attaining its adult size ? While the Lithothamnion is 

 encroaching upon it from one side, plenty of time would be available for extension 

 of the coral to take place in the opposite direction. Although no reason whatever 

 could be discovered, it seems to be the fact that a coral once attacked by the 

 Lithothamnion remains stunted ; for even quite small coralla, of P. grandis for instance, 

 were met with completely encrusted. 



As to the conditions, favourable or unfavourable, to the production of numerous 

 individual coralla, as distinct from the rate of growth of individual coralla, nothing 

 whatever was discovered. Those great factors, to which one naturally looks, ocean 

 currents and the direction of the trade- winds, appear to have nothing to do with it, at 

 least at Funafuti. It is to be regretted that no more definite statement can be 

 made in regard to Lithothamnion growth. The estimate, however, of its extremely 

 slow growth, seems to be confirmed by the fact that only on rare occasions is the 

 Lithothamnion met with in a state which indicates that the deepest laminae are of 

 recent origin in layers more than three-quarters of an inch in thickness. 



It may be stated here that on some of the Gilbert Islands, Onoatoa for instance, 

 a very thickly digitated Lithothamnion seems, in places, to be forming the entire 

 ocean platform. These islands were visited on the home journey of the Expedition, 



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