1904] MAC DOUGAL—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 
Fic. 7.—Desert of Baja California; view from San Felipe Bay; peak over rooom 
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 
