86 
know it well, no matter how familiar he may be with specimens in a 
museum, until he has seen the locality of its native occurrence. 
As for life-zones of the section, my brief and superficial survey, 
taking into account almost altogether the more conspicuous plants, in- 
dicates the following succession from west to east. (1) Upper Sonoran 
zone, in the immediate vicinity of San Diego (within the range of first 
effects of the sea breeze); (2) Lower Sonoran zone, dilute in degree, 
occupying a belt from a few miles out of San-Diego to the vicinity of 
Jamul; (3) Upper Sonoran zone again, comprising the almost continu- 
ous chaparral belt from the last named point through to the vicinity 
of Jacumba; (4) Lower Sonoran zone, from the broad area of gradual 
blending marked centrally at the last named point and beginning pure- 
ly at the edge of the declivity above Mountain Springs. A noteworthy 
feature, another surprise to one previously familiar only with topo- 
graphic maps, was the total lack along the route traversed of the faint- 
est representation of the Transition zone. The Mexican boundary of 
California cuts only the Austral life zones. There is no continuous high- - 
way for Boreal species south into the mountains of Lower California. 
