288 D. Praiii — The Vegetation of the Coco Group. [No. 4, 



scarce ; the only exceptions are Turhinaria ornata, which is fairly frequent 

 both on the coral reefs and on the sandstone ledges ; Padina joavonia, 

 more common on the exposed sandstone reefs but less frequent on the 

 coral than Turhinaria ; and Sargassum ilicifolium, which is the only really 

 common seaweed and which occurs in great meadows at the outer margins 

 of the fringing reefs and sandstone ledges that are exposed at low-tide, as 

 well as in the deeper water beyond. 



Reefs such as those described are extremely common in all the 

 islands of the Andaman and Nicobars groups that the writer has visited, 

 and the marine vegetation is remarkably uniform in appearance as well 

 as in specific constituents. On Car ISTicobar, for example, as well as on 

 Rutland Island, at the extreme south end of the Andaman main group, 

 localities which the writer has visited on different occasions, it is 

 hardly possible to detect a species not represented on the reefs of the 

 Cocos. On similar reefs in South Andaman, however, a second species of 

 Gymodocea, quite as profuse where it exists, but more local in its occur- 

 rence, has been gathered, and on a similar reef in Little Andaman large 

 meadows of HalopMla ovalis were found associated with those of Gymo- 

 docea. The beach betweeii such a reef and the Pandanus sea-fence con- 

 sists, so far as the writer's observations extend, almost exclusively of 

 coral sand mixed with small shells or fine fragments of large shells. The 

 heavy surf in such a bay as this breaks at the outer margin of the reef, 

 and even at high-tide in rough weather the swell is so weakened there 

 that the waves which break on the beach are not so heavy as to have 

 any great erosive power. Indeed their effect appears to be on the whole 

 accretive, for the sand that accumulates at the head of the bay becomes 

 bound by Ipoinoea biloba, Sesiivium, Uuphorhia Atoto, etc., the Pandanus 

 fence encroaches on the beds of Ipomoea ; the coco-nut zone widens sea- 

 wards, and behind it the first line of beach-forest, containing Termmalia, 

 Heniandia, Erythrina, Pongamia, Stephegyne, Thespesia, and the second 

 line of the same forest, characterised by Mimusops, Gyrocarpus, Pisonia, 

 Ardisia, Gycas assert themselves in an area previously covered by the 

 tides. In certain situations, too, the true mangroves stalk forward into 

 the tolerably quiet waters of these bays, while in a different but equally 

 effective manner, by sending up suckers from among its curious pith-like 

 roots, Avicennia establishes itself upon the reef. The gtiyed and stilted 

 habit of the former makes their position very secure ; the latter, 

 from the enormous area covered by its roots, must also be difiicult to 

 overthrow. The process of land-making behind a fringing reef, either 

 as a sandy flat covered with coco-nut trees, or as a mangrove swamp 

 spreading seawards, is well exemplified in the two bays lying respec- 

 tively to the south and to the north of the position of the first season's 



