Vol.1] Hall. — Botanical Survey of San Jacinto Mountain. 51 



There are two possible solutions to this problem. The first 

 is that the seeds may have been carried across the desert, in 

 either the one direction or the other, by birds or other animals. 

 It must be remembered, however, that the distance from the 

 San Jacinto Mountains to those of Arizona is something over 

 two hundred miles, that the seeds of these species have no 

 particular devices to aid in theu' dissemination, and that seeds 

 peculiarly adapted to dissemination over large areas have not 

 been able to cross this barrier. 



The second and more probable explanation is that we here 

 have the remnants of boreal species which were driven from 

 their northern home during the glacial period and which, being 

 for some reason unable to retreat to the north at the close of that 

 period, became stranded on these widely separated mountains, 

 to which they had flown for protection from a climate gradually 

 increasing in warmth and aridity. It is to be noted that one of 

 these plants, the Geranium, occurs in the Rockj^ Mountains at 

 least as far north as Idaho and further exploration may extend 

 the ranges of all of them along both the Rockies and the Sierras. 



We may then conclude that the flora of San Jacinto Mountain 

 is composed of a boreal and an austral element, that the presence 

 of the former is due to the fact that northern species were forced 

 southward along the Sierra Nevada and San Bernardino Moun- 

 tains during the glacial period, while of the species belonging to 

 the latter a part are native to Southern California and a part 

 have been derived from the regions lying to the southeast. 



CATALOaUE OF SPECIES COLLECTED IN OR ABOVE 

 THE YELLOW PINE BELT. 



In preparing this list of San Jacinto Mountain plants, it has 

 seemed advisable to exclude the foot-hill flora, since it is so 

 largely composed of species more or less common in similar 

 regions throughout Southern California; therefore only those 

 species occuring in or above the Yellow Pine belt have been 

 listed. It is to be noted, however, that foot-hill species are in- 

 cluded if they occur on any of the "Sonoran islands," that is. 



