TPIE BIOLOGY OF THE FUNAFUTI ATOLL AND REEF FORMATION. 145 



since the pieces did not seem to be thriving after they had been removed to the place 

 of observation. 



(10) Of the Lithothamnion, experiments were made only on the lichenous form. 

 It was not found possible to obtain even the slightest indication of increase during 

 five months of patient observation, by any one of the methods adopted, viz., by 

 measuring between the opposite points of the channels on the platforms, by the 

 insertion of glass pins and rods, by the employment of markings and scratchings in 

 the Lithothamnion substance, by the implanting upon it of foreign objects, so that 

 the growth indicated by strength of cohesion might be noted, and by sundry other 

 means. 



Certain information, however, was gathered which, although it throws no light on 

 the rate, yet makes clearer the mode of growth of this alga. 



Its landward limit is, as elsewhere stated, the wash of the waves of low-water 

 spring tide. Occasionally one finds, just outside the limit, isolated patches from 

 1 to 6 inches in diameter, which, like the rest, are of a bright pink colour, and 

 very well defined from the remainder of the reef rock. Yet so extremely thin are 

 these growths that it is quite impossible to feel, much less to measure, their thick- 

 ness, and were it not for their colour there would be nothing to indicate their 

 presence on the platform. Several of these patches were measured from week to 

 week, and an average growth of expansion of 1 inch in 10 months was determined, 

 while in one instance an extension outwards at the rate of 1 inch in 6*56 months was 

 shown. 



Again, on several occasions the weather at spring tide Avas exceedingly calm, so 

 that the wash at lowest ebb did not reach up to its usual mark, with the result 

 that considerable areas of Lithothammon, especially on the mounds surrounding the 

 heads of the channels in the seaward face of the reef platform, remained quite dry 

 and exposed to the sun for upwards of an hour. This exposure caused them to turn 

 completely white, indicating thereby the death of the alga so affected. After a few 

 days, however, the pink colour began to reappear, always having for its starting point 

 some notch in the edge of the white patch, or some slight hollow, or small hole in 

 its mass. Growth from these centres would proceed concentrically until, eventually, 

 the several advancing portions met and again completed the sheet of colour. This 

 would occupy less than two weeks. Several specimens of this kind, showing the dead 

 and regenerating portions, were preserved in spirits, formalin and glycerine. 



Extremely minute as it is, the growth indicated by the two above-mentioned 

 observations must mean in yeai-s an addition to the atoll. Indeed, it seems quite 

 possible that the mounds so conspicuous at the ends of the channels, in the very 

 places where the above-mentioned observations were made, are partly due to this 

 growth of layer upon layer of new material.* 



(11) Halimeda. Of the other Algse this great debris producer received special 



* Foraminifera, such as Polytrema and CarjJenteria, contribute largely to form these mounds. 



U 



