12 ALLAN HANCOCK PACIFIC EXPEDITIONS VOL. 13 



Stature, densely spaced, with epiphytes common in the more humid locali- 

 ties. On the mainland of Mexico, the Sinaloan flora occupies the low 

 and middle elevations from southern Sonora south at least to Nayarit. 

 Farther south it is local or transitional with the Central American floral 

 element. The Velero III collections from the Tres Marias Islands, the 

 Revilla Gigedo Islands, and the Cape District of Baja California are 

 referable to the Sinaloan flora. 



(4) The Central American flora is distinctly tropical under medmm 

 to high rainfalls. It contains a very great number of species and is domi- 

 nated by both evergreen and deciduous trees of medium to tall stature. 

 It is further characterized by broad leaf blades and an abundance of epi- 

 phytes. The Pacific part of the area is distinctly arid as compared to the 

 Atlantic, and its coastal forests are mostly deciduous, of medium stature, 

 and are interspersed with areas of savanna. There is a long dry season 

 from November to May. From the standpoint of vegetation there is 

 little to separate the Pacific coast of Costa Rica from the Pacific coast 

 of southern Mexico, since the dominating plant forms and associations 

 apparently extend throughout with but little modification as far north 

 as Nayarit. The Velero III collections from coastal Jalisco, Oaxaca, and 

 Costa Rica reflect this general relationship. 



The report has been organized according to geographic regions under 

 the following headings: The Channel Islands of California, Cedros and 

 San Benitos Islands, Revilla Gigedo Islands, Tres Marias Islands, The 

 California Gulf Region, Jalisco and Oaxaca, Mexico, and Costa Rica. 

 The desirability of so enumerating these scattered collections, representa- 

 tive of several regions and several floras, is so obvious it is unnecessary 

 to recount them here. Each section is introduced by a general discussion 

 of the physiography, the climate, and the plant geography with special 

 emphasis on the historical or developmental aspects of the. flora involved. 

 I have also attempted to evaluate the botanizing that has been done to 

 date on the respective areas, the islands in particular. The discussions 

 are opinionated summaries, according to my experiences and observa- 

 tions in the fields or to reports read, rather than documented conclusions. 

 It is hoped that they will stimulate interest and activity in the richly re- 

 warding botanical field of northwestern Mexico. 



As is usual in works of this kind, the author is indebted to many 

 people for their willing assistance in making the report possible. To all 

 of them he extends his sincere thanks. Ira L. Wiggins of Stanford Uni- 



