28 Annals of the Carnegie Museum. 



faces the sea in a more or less prominent, perpendicular, and ex- 

 tremely jagged cliff, broken here and there by inlets and sandy beaches, 

 but constituting, altogether, a dangerous coast with but very few 

 harbors. This "South Coast" plain has a very scanty, but yet rich, 

 dark, loamy soil filling the holes and pockets in the jagged surface 

 of the rock and supporting a hardwood forest with many large trees. 



The climate of the island is, of course, oceanic and equable. The 

 extreme annual range of temperature lies between 50° and 100° Fahr., 

 the temperature during May, 1910, ranging from 82° to 92° during 

 the warmest part of the day, the minimum rarely falling to 70° at 

 night. The water taken from the wells and springs usually registered 

 between 70° and 80° Fahr., while the temperature of the ocean water 

 on the beaches was 8o°-82° Fahr. 



The season is sharply divided into a wet season and a dry season. 

 The rains, frequently torrential thunderstorms, occur from May or 

 early June to about November, then occur scattering showers until 

 early spring, followed by a severe drought till the rains begin again. 

 The drought must be ecologically a very important factor in deter- 

 mining the character of the vegetation of the island, particularly 

 where associated with extensive grass and brush fires, as appears to 

 have been the case at least since the occupation of the island by 



Europeans. 



Plant Associations. 



The vegetation of the various parts of the island is very closely 

 related to the major features of the physiography and geology as 

 outlined above. Briefly, the following ecological groups are out- 

 standing features of the landscape. For purposes of uniformity 

 the nomenclature adopted for these groups is essentially that of 

 Harshberger's Phytogeographic Survey of North America. 



I. The Mangrove Forest Formation. 



This formation consists of a low thick forest of halophytic shrubs 

 fringing the low coasts of the island and extending inland, particularly 

 along the lower courses of the rivers, up to the limits of brackish water. 

 Towards the mouth of the Nuevas River, in particular, the man- 

 groves have been instrumental in catching and retaining river sands 

 and coastal debris to the extent of adding considerably to the area of 

 the island. 



The margin of the mangrove forest nearest the water consists, in 



