Island. This has been reported to be mainly a result of salinity of the ground water (Fosberg, 1949). One seep at the edge of the present lagoon contained 75.2 ppm of salts almost double that of sea water. In the case of some of the drier islands [illegible] this interior may be affected lay. with enclosed lagoons, the of the island results in an increase in the salinity due to the closed nature of the lagoon and the evaportaion of standing sea water seepage from shallow surfaces. [illegible] may accentuate the importance of salinity and One possible factor of importance its effect in the salinity gradients of dry islands would be the increase on the of salinity in the lagoon which goes hand in hand with the closing off vegetation of channels. One interesting case is that of Sydney Island a small atoll which has been an enclosed lagoon cut off within historic time much like the one at Enderbury. A sample of water taken from the lagoon water in the vicinity of islets along the NW shore evidenced a slainity of 166.0 ppm, nearly five times that of seawater. This increase in salinity may control to a great extent the species found considering the species found in at present on the dry islands working from the lagoon to the outer beach. There is a suggestion that the dying Pisonia on Gardner and Sydney may be due to a combination of [illegible] the lack of rainfall and an increase in salinity of normally tolerable levels of salinity associated with the lense of freshwater. One of the village wells 2.2 m. deep on Sydney contained brackish water in October 1964. If rainfall two bore pits were tested, both were brackish but a reed was growing in one. is negligible and evaporation continues over a long period the fresh water lens may be exhausted in some areas particularly in narrow sides of islets and enclosed islands. Saline waters [illegible] tend to be replacing these at levels where the roots of shrubs and trees penetrate. An unusually high salinity in waters underlying the islets would raise the salinity of the groundwater and may contribute to the irregular pattern of vegetation associations or distribution of species on dry atolls. The Pisonia groves of both Gardner and Sydney Islands are dying or in a state of extreme drought. This is a species usually identified with the more mesic sites of a coral atoll. It is suggested that the increased salinity of lagoon waters due to the enclosure of a once open lagoon may be partly responsible due to the raising of the salinity of the groundwater. This with the prevailing drought may be responsible for the apparent dying back of potential Pisonia groves on these islands.