K)04] 



MAC DOr GAL— DELTA AND DESERT VEGETATION 



57 



received during the year 1903, the relative humidity at all times being 

 very low also. The rainfall is distributed throughout the year, so 

 that only a small proportion of the total is received within any month; 

 furthermore, this distribution is irregular in any series of seasons, 

 so that the native plants have but little opportunity of acquiring a 



Fig. 7. — Desert of Baja California; view from San Felipe Bay; peak over iooo m 

 high, ascended February 14, 1904, in distance; the sloping plain which rises gradually 

 to the foot of the mountain bears Fouquieria, Ephedra, Covillea, Bursera, Parosela, 

 Parkinsonia, and Cereus. 



rhythm of activity in response to the annual supply of moisture, a 

 fact not without its influence on the general anatomical character of 

 the plants, as will be pointed out below. In no part of the country 

 to the southward of Yuma did we find any evidences of a greater 

 rainfall than that given above, upon noting the surface of the soil 



