LAND PLANTS COLLECTED BY THE VELERO III, 

 ALLAN HANCOCK PACIFIC EXPEDITIONS 1937-1941 



(Plates 1-15, Maps 1-3) 

 By Howard Scott Gentry 



General Introduction 



The complete itinerary of the voyages of the Velero III on the Allan 

 Hancock Pacific Expeditions is given by Eraser (1943). An outline of 

 the land plants secured are given in Table 1. Since the expeditions were 

 primarily concerned with marine biology and especially the collection of 

 marine faunas, the land plant collections were only incidental and are 

 not large. They are samplings of several distinct floral elements of west- 

 ern North America. 



( 1 ) Those from the Channel Islands belong to the unique California 

 flora, in one of the five regions of the world having a Mediterranean 

 type of climate. This climate is characterized by winter rainfall, dry 

 summers, and maritime influence conducive to equable temperatures, on- 

 shore winds, and regular seasonal fogs. Cedros Island, off the west coast 

 of middle Baja California, contains in its high elevations a southern out- 

 post of the California flora. 



(2) The Sonoran Desert flora is generally peripheral to the Gulf of 

 California. It extends farther south on the peninsula (to the Cape Dis- 

 trict) than it does on the mainland (to about Guaymas, Sonora). In its 

 area an arid contintental type of climate competes with an arid maritime 

 one, the former most evident in the northern part of the region around 

 the lower Colorado River basins, while the latter is particularly stead- 

 fast in the middle and southern outer coastal part of the peninsula. 

 While both types have low and irregular rainfalls, the maritime desert 

 differs in having more equable annual and daily temperatures, higher 

 relative humidity, and summer rainfall is more common in the southern 

 latitudes. This latter feature is a tropical factor in the situation. 



(3) The Sinaloan subtropical flora is the great transitional element 

 between deserts and tropics. Rainfall is about 90% summer. The high 

 temperatures are ameliorated, particularly through the spring, by on-shore 

 westerlies. The dominating life form is the tree of short to medium 



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