A technique has been devised to study changes in the xylem-sap tensions in Cocos using a pressure bomb. Preliminary studies indicate that xylem tensions range from 2 to 13 bar depending on solar radiation and other environmental changes. One surprising observation is that xylem sap tensions are somewhat lower in the dry season, apparently due to earlier stomatal closure during the mid-late morning. Despite the close proximity of lagoons of saline water, there was no indication that the uptake of water was reduced through osmosis, and a hidden supply of fresh water is implied. Finally, some precautions are listed which avoid certain anomalous results using the pressure bomb.