64 ALLAN HANCOCK PACIFIC EXPEDITIONS VOL. 13 



latitudes. The members of the California Academy of Sciences Expedi- 

 tion to the islands in 1922 found the vegetation dripping with early 

 morning fog around the summit of Mount Evermann. These fogs 

 ameliorate the spring aridity and help support the epiphytes of the mon- 

 tane forest, and even the tree growth by reducing transpiration. 



The total known flora of this archipelago consists of only 120 vas- 

 cular plants (Johnston 1931) ; Socorro 102 species, Clarion 43 species, 

 San Benedicto 11 species, and is based upon about 325 numbers col- 

 lected by five men. Table 3. All of these collections but one were made 

 in the spring dry season. Barkelew only collected during the summer 

 months (May 15 to July 8) and he apparently failed to exploit fully 

 the opportunity to obtain representatives of the rich upper canyon flora. 

 It is not known if the summer rains preceded him. I have not seen his 

 specimens, which would indicate the condition of the vegetation at the 

 time of his visit. As on the Mexican mainland, collecting on the islands 

 should be best from August through November and the first botanist 

 to engage the flora at this season will undoubtedly be richly rewarded 

 with plants and information. Johnston (1931) has given good geo- 

 graphic descriptions of the islands, and with his and Hanna's reports 

 (1926), I have drawn up the following brief summaries of the islands. 



TABLE 3 



Socorro Clarion San Benedicto 



"Vcsr Collector ■ " , ' ' ■ , ^ 



spring summer sprmg summer sprmg summer 



10? 



Total known species 102 43 11 



Table 3. Plant collectors and their collections from the Revilla Gigedo Islands. 



San Benedicto Island. 48 kilometers north of Socorro, is about 5 

 kilometers long, averages about 1 kilometer wide, and contains in the 

 neighborhood of 5 square kilometers. The southern half is an ash cone 

 about 296 meters high, the northern half a lava plateau. Physiographi- 

 cally it is young and little developed with a poor diversification of 

 habitats. The known flora consists of but 1 1 species of land plants. 



Clarion Island, the extreme western outpost, is roughly rectangu- 

 lar, about 8 kilometers long, 3 kilometers wide, and 24 square kilo- 

 meters in area. It is surrounded by an immature coral reef (Hanna, 



