DESERT REGIONS OF NORTH AMERICA. 43 
resin so copiously as to make a distinct deposit on the ground underneath 
the low-spreading branches. 
The streamways leading down from the mountains were inhabited by 
a number of eriogonums and euphorbiaceous herbs. A few opuntias 
of the cylindrical arboreous type (plate 47), an Echinocactus, a Cactus, 
and a small Cereus were also seen. Pulocereus sargentianus, which is 
found on the mainland far southward, here reaches the greatest density 
yet observed, forming forests many acres in extent. Perhaps the most 
notable feature from a geographical point of view was shown by the pres- 
ence of a great tree-cactus having the appearance of Cereus pecten- 
aboriginum. Cereus pringletis known to be abundant, under the common 
name of ‘“‘cardon”’ farther south, but this plant appears to agree with the 
former and makes a splendid picture in the arid landscape, finding here 
its extreme northern limit of known occurrence. 
The large number of species with laticiferous juices was especially 
noticeable, but with the exception of the dozen cacti no plants with 
organs for storage of water were seen, a fact possibly connected with the 
extremely low precipitation and low water content of the soil at all times. 
Seeds of a Cenchrus were very abundant and were used by burrowing 
rodents as a means of fortification of the entrances to their burrows, in 
the same manner that the joints of the ‘“‘cholla’’ are employed elsewhere. 
A mountain to the southwestward of San Felipe Bay was climbed and 
a summit reached at an elevation of about 3,500 feet. The granite 
slopes supported a sparse vegetation of such types as Cactus, Ephedra, 
Terebinthus microphylla, Asclepias albicans, Eriogonum tnflatum, Yucca, 
Agave, and Opuntia. So far as might be estimated by the instruments at 
hand, the mountain is probably the one on the hydrographic map of 
1873-75 designated as a ‘“‘sharp white peak 4,288 feet,’”’ which had not 
previously been ascended and still bears no name. 
The rainfall is apparently distributed throughout the year, so that 
only a small proportion of the total is received within any month; further- 
more, this distribution is irregular in any series of seasons, so that the 
native plants have but little opportunity of acquiring a rhythm of activity 
in response to the annual supply of moisture, a fact not without itsinfluence 
on the general anatomical character of the plants. 
Dr. Edward Palmer visited the Razu Islands, in the lower part of the 
Gulf, 200 miles northwest from Guaymas, in February, 1890, and noted 
that no rainfall had been received there for more than a year. Nothing 
can be hazarded as to the extent of the region with this extreme limit of 
aridity on the Sonoran side of the Gulf, except that it does not appear to 
include the western slope of the central range in Baja California, although 
no definite information is available. It is evident, however, that a 
further investigation is necessary to determine the exact meteorological 
status of this region, as well as the general character, derivation, and 
