74 I. M. JOHNSTON 



are compared with the San Jacinto 3 or San Bernardino 4 Moun- 

 tains. The writer hopes that the following paper, while only- 

 dealing with a limited portion of the San Gabriel Mountains, will 

 be a contribution towards the desired knowledge of their flora. 



Three life zones are distinguishable in the San Antonio Moun- 

 tains : the Upper Sonoran, Transition and Canadian. The Upper 

 Sonoran Zone includes the bases of the mountains, never ascend- 

 ing higher than 6000 feet altitude. This zone is recognized at 

 once by the presence of dense thickets of shrubs, called chaparral, 

 which cover the mountain side. The chaparral belt does not 

 have its twenty-five or more component shrubs in an unvarying 

 mixture, for not only are some species restricted geographically, 

 but on the coastal slope, in response to differences in moisture 

 and temperature, two distinguishable life belts have been formed 

 within the chaparral belt. These are hereafter designated as the 

 "Upper" and "Lower Chaparral Belt." The Lower Chaparral 

 Belt is characterized by the dominance of such shrubs as, Adeno- 

 stoma fasciculatum, Quercus dumosa and Ceanothus crassifolius. 

 On south facing slopes these plants grow abundantly below 4500 

 feet altitude, on north slopes they seldom reach an altitude of 

 3000 feet. The Upper Chaparral Belt, on the other hand, is 

 found usually above the 4500 feet contour on south slopes, and 

 never lower than 3000 feet on north facing slopes. Arctostaphy- 

 los tomentosa, Quercus Wislizeni and Ceanothus divaricatus are the 

 dominant shrubs in the Upper Chaparral Belt. 



Since we have not visited the desert base of the mountains we 

 are unable to discuss its Upper Sonoran flora. Because of this 

 fact and because the composition of the chaparral is well known 

 and similar to that found in adjacent territory we have not 

 included the chaparral flora in the catalogue which forms the 

 bulk of this paper. 



3 Hall, H. M. A Botanical Survey of the San Jacinto Mountains. Univ. Cal. 

 Pub. Bot. 1: 1-140, 1902. 



4 Parish, S. B. An Enumeration of the Pteridophytes and Spermatophytes of 

 the San Bernardino Mountains, California. Plant World 20:163-178; 208-223 

 and 245-259, 1917. 



