62 BOTANICAL GAZETTE [JULY 
regions with fringing mud banks derived from the river deposits. 
The greater part of the vegetation of the coastal slopes and plains, 
however, is made up of species which also extend southward along 
the shores of the Gulf, and are found but sparingly to the northward. 
The vegetation of the Salton basin is subjected to the action of 
extreme aridity and also of a high concentration of soil salts, com- 
prising types of the most pronounced character, both of halophytes 
and xerophytes. The elevations included in the delta are dry moun- 
tain slopes and support a desért vegetation. 
The mesas adjoining the northern part of the Gulf of California 
appear to offer the most extreme desert conditions in North America. 
The rainfall at Yuma at the northern extremity of the delta was less 
than 25™™ during 1903, and years have been noted at points farther 
south in which no precipitation occurred. The entire normal pre- 
cipitation in the desert in Baja California is probably no greater than 
the amount of water condensed as dew in eastern United States. 
The desert apparently extends to the slopes of the central elevation 
of the peninsula to the westward, which reaches an elevation of over 
3000". This mountain wall probably acts as a barrier which shuts 
off moisture-laden winds from the Pacific and causes the aridity of 
the region. The southern and eastern limits of the extreme desert 
cannot be defined with the information now at hand. 
The vegetation of the desert areas in the regions of greatest aridity 
consists chiefly of types devoid of massive storage organs, and of 
perennials with laticiferous sap, while a large number of forms secrete 
volatile oils or exude resinous gums. The determination of the 
causal relations of these adaptations cannot be made safely by a 
general interpretation of the aspects of vegetation, but it is to be 
seen that in a region in which surplus rainfall or ground water never 
occurs, storage organs would be manifestly useless, and indeed their 
formation impossible. Species with spinose branches and minute 
leaves which are quickly discarded during unfavorable periods are 
abundant. Several species of Ephedra with functionally ‘useless 
leaves and chlorophyllose stems are included, while Lycium and 
Frankenia with small succulent easily detachable leaves are highly 
characteristic of some localities; the last-named species are about 
