The vegetation The natural vegetation of Christmas Island is characterized by xeric and semi-xeric Pacific strand species such as Portulaca lutea, Heliotropium anomalum, Scaevola and Tournefortia. (Christophersen, 1927). These herbs and shrubs along with Sida, Suriana, Hedyotis and Lepturus form distinct associations which at one time covered the atoll, the largest in land area found in the world. The island appears to have been created from a group of smaller islets which were united by storm and wave deposited debris and, possibly, uplift. (Rougier, 1914). These old islets forms the upland areas of the island which are covered with a Scaevola-Tournefortia association mixed with open areas of Sida and Lepturus. A banded type of association arrangement is found around the shores of the inner lagoon and lagoon flats where a Suriana-Hedyotis association is common above the periodically flooded areas. An under- growth of Sida, Lepturus and Portulaca is common in open areas between the edge of the lagoon and the Scaevola scrub. Sesuvium forms associa- tions with Eragrostis whitneyi and Heliotropium at the lagoon edge or on the raised islets of the lagoon area. Often Sesuvium forms pure stands in these areas. In 1965 a Cuscuta sp. was discovered on one islet in the heavily dissected area of the lagoon in the middle portion of the island. A number of islets were inspected but no other lovale was found for this undetermined species. Lepidium bidentatum occurs in dry open areas near the lagoon on the SW end of the island. The three islets of the Christmas atoll are interesting in that some but not all of the species found on the larger island are represented in a relatively small area. Cook Island is sparsely covered, in some places just at the periphery, with the Scaevola-Tournefortia association. Heliotropium and Portulaca are found on the dry open portions with Lepturus and Sida forming a relatively thick cover on the S end of the island. Cassytha is found on the Boerhavia, Scaevola, Portulaca and Sida. The soils are made up of sand and coral rubble. The two smaller islets of Motu Upua and Motu Tabu are sand islets with Scaevola - Tournefortia scrub. On Motu Tabu a Pisonia tree to 5 m. is found in the center of the island and several small Hedyotis shrubs were found on ;the E Shore just above the high tide line on the sand and gravel beach. Seedlings of Tournefortia, Scaevola and Eragrostis whitneyi were found in pioneer areas of newly deposited sand on the E side of Motu Tabu and Motu Upua. Tribulus cistoides and Boerhavia repens are found on all three islets sometimes forming thick mats of over- lapping stems. These species often form a considerable litter. The S area of the island was surveyed in 1965. Of special interest was the ground zero area of the 1957 bomb test site and adjacent areas to the north of the site. The vegetation in the S area consists at pres- ent of Lepturus - Sida stands with Portulaca and Boerhavia. Tribulus is found in patches. This vegetation type approximates that which was present before the tests. The Scaevola - Tournefortia cover on the S part was almost completely eliminated. In 1965 the dead remains of large Tournefortia trees were to be seen. Scaevola scrub appeared to be recovering by sprout- ing from the base. Some of these were 1.5 - 2.5 m. high. New plants probably from seedling were evident along the south shore. Nesting bluefaced boobies and sooty terns were present in these open areas in large numbers.