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3 
1904] MAC DOUGAL—DELTA AND DESERT VEGETATION 61 
In shade of Bursera. 
At 76™ level, 13*™ from shore. 
Feb. 13 1:00 P.M. ‘page 40% rel. hum. 
“cc 13 6:15 (23 57 (73 “ec 
Saal 6:00 A. M. es 33 a 
800™ on mountain. ' 
Feb. 14 8:45 A.M. 69° F. 32% rel. hum. 
1200™ on mountain (jig. 7). 
Feb. 14 II:00 A.M. ree oe 32% rel. hum. 
Small mountain too™ high, 20*™ north. 
San Felipe, 8" from coast. 
Feb. 19 9:45 A.M. mee 18% rel. hum. 
RESUME. 
It is to be seen that the region discussed in the foregoing paper 
includes a subtropical delta of irregular outline and long extensions, 
which includes within its outermost boundaries a great alluvial plain 
subject to floods, bank erosion, and shifting of the soil, and also to 
the action of salt tidal waters; a mountain range of granite and vol- 
canic rocks over 1000™ in height; a small area of active mud volcanoes; 
a depressed region, presumably an old sea-floor, the bottom of which 
is more than 100™ below the level of the sea; and the mud flats near 
the actual mouth of the river. This delta is directly in contact with 
the gravel and sand desert mesas of Sonora and Baja California. 
The portion of the delta subject to the direct action of the floods 
and tides is everywhere slightly alkaline and varies but little in the 
general constituency of the soil, supporting a luxuriant growth of 
vegetation, the more important elements of which grow in pure for- 
mations of the 2 greatest possible density. The larger woody plants of 
this region have their bases submerged in water at a low temperature 
during the summer season, during which time the crowns are exposed 
to low relative humidity at temperatures that may be as much as 
70° F. higher than the roots. In consequence of this condition many 
Species in the low lands have xerophilous foliage. In addition, a 
comparatively high concentration of soil salts must be endured during 
the stages of low water. 
An analysis of the flora of the region shows that many of the 
Species of the delta extend down along the coast especially in the 
