VEGETATION OF MT. ST. HELENA. 107 



about Mt. Diablo; especially is this obvious in the long, dry, rainless 

 season. 



But when we ascend each of these mountains we find the soil 

 conditions very dissimilar, the sides of Mt. Diablo being covered 

 with fairly fertile soil quite to the summit. This factor then must 

 account primarily for the striking differences in the character of the 

 vegetation. The herbaceous vegetation of the summit of Mt. Diablo 

 is in general rich both as to number of species and individuals, while 

 St. Helena is defective in both of these particulars. Shrubs as to 

 individuals abound on both mountains but the former mountain has 

 the advantage in number of species. The shrubs of Mt. Diablo are 

 invariably those species characteristic of the dry interior ridges. 



Notwithstanding the arid character of the summit of Mt. St. 

 Helena, it possesses a few species characteristic of the humid Coast 

 region or of the High Sierras and other elevated mountain ranges, 

 such as the Douglas Spruce (Pseudotsuga taxifolia), and the 

 Flowering Dogwood (Cornus Nuttallii); although the latter can 

 scarcely be said to belong to the summit of the mountain, it ascends 

 to points above the beginnings of the volcanic ash. Three species 

 of Ceanothus, C. velutinus var. Isevigatus, C. prostratus, var. diver- 

 gens, and C. foliosus, all found on Mt. St. Helena, are not found in 

 the Inner North Coast Ranges nor yet on Mt. Diablo. Otherwise 

 the species are almost entirely those characteristic of the more arid 

 districts of California. 



The vegetation of the summit is distinguished by the prevalence 

 of shrubs of a limited number of species which completely mantle 

 the shoulders and enwrap the sides of the mountain above 2,300 to 

 2,500 feet. Arctostaphylos manzanita is very abundant, particularly 

 at the highest elevations, and numerically outranks all other species. 

 Gart-ya Fremonti is fairly common, and Xylothermia montana, 

 Rhamnus Californica and Ceanothvs foliosus are very frequently 

 met with. A fine thicket of Castanea chrysophylla is to be found on 

 the ascent to the second summit. Two species of oak, Quercus 

 chrysolepis and Wislizenii, are represented by scattered individuals. 



Two other low shrubs, neither of them abundant, were found, viz., 

 Dendromecon rigidium and Eriodictyon Californicum. The only 

 trees were two species of Coniferse. Pinus attenuata is scattered 



