14 University of California Publications. [botany 



Sonoi-aii. We thus liave the six zones very much crowded 

 together, and the upper four ahnost in superposition. There is 

 probably no place in North America where the alpine and 

 Sonoran floras are in such proximity as they are on San Jacinto 

 Mountain. 



Tn working on the flora of the mountain it very early became 

 evident that the vegetation of the lower part of the Transition 

 Zone was quite different from that of the upper part, and that 

 the ranges of many species could be more concisely and definitely 

 given by applying distinctive names to each of these parts. For 

 this purpose the names Lower Transition and Upper Transition 

 have been selected, but this will not preclude the use of 

 the term Transition when it is desired to speak of the two parts 

 taken as a whole. Whether or not this division will be of service 

 in working out the distribution of plants on other mountains 

 remains to be seen. 



The line l)etween the Upper and the Lower Transition is 

 naturally not so distinct as those between the primary zones. 

 On San Jacinto they may be distinguished by the presence or 

 absence of certain trees and shrubs, among which the Yellow 

 Pine and the White Fir are the most serviceable, the former 

 being dominant in the Lower and the latter in the Upper Transi- 

 tion. We cannot depend entirely upon these two trees, however, 

 to mark the two zones, since the fir is also present as scattered 

 specimens in the LoM'er Transition, while the pine occurs at some 

 places in the Upper Transition, although not as the dominant tree. 

 While it must be admitted that the moisture conditions affect 

 materially the distribution of these species, the fir requiring a 

 moister soil than the pine, yet this is not an important consider- 

 ation so far as their use as zone indicators on this mountain is 

 concerned, since as the altitude becomes greater the temperature 

 of the ail' is reduced and the moistui'e in the soil increased. More- 

 over the effect of such factors as slope exposure and desert 

 winds is the opposite of that produced by an increase in altitude. 



If it is desired to carry this distinction between the Upper 

 and Lower Transition to other mountains it will probably be 

 found necessary to resort to other species to indicate these zones, 

 and it is partly for this purpose that a list of the shrubs charac- 

 teristic of each is here inserted. 



