4 f PREFACE. 



species as Ceanothus cuneatus, Arctostaphylos manzanita and tomentosa, Pick- 

 eringia montana, and Quercus dumosa and wislisenii var. frutescens. By 

 reason of the uniformity of the conditions governing growth in the chaparral, 

 the very low water content of the rocky or gravelly slopes, the high summer 

 temperature and high Insolation, these shrubs presenl a similar aspecl by virtue 

 of their uniform height, reduced leaf surface, frequently thorny or thorn-like 

 branchlets and rigid branches. The open slopes of tins region, the slopes 

 and low liills destitute of woody growth, are extensive and covered in the 

 ative season with a growth of grasses and perianth-bearing endogens 

 and exogens developed in considerable richness. Some of the species most 

 abundant in individuals and consequently in wide arms the dominating species 

 of the vernal flora arc as follows: Avena fatua, Vanthonia californica, Festuca 

 myuros, Lolium temulentum, Mordeum nodosum and murinum, Brodiaea capi- 

 tata, "Ranunculus californicus, TAnanthus parviflorus, Phacelia distans, Plagio- 

 bothrys canescens, Orthocarpus erianthus, varieties of Afimulus langsdorffi, 

 Castilleia foliolosa and Baeria chrysostoma. These species, not to include 

 very many others, arc widely distributed in both the North Toast Ranges and 

 the South ('oast Ranges, ranges lying respectively north and south of the Bay 

 of San Francisco and its connecting arms. The Golden Gate and San Francisco 



Bay represent, however, a not unimportant natural harrier, since many species 



of the Oregon and Washington flora range southward in the North Coasl 



Ranges as far as San Francisco Bay, and similarly many species of Southern 

 California range northward as far as the Santa Cruz Mountains or Mt. Diablo. 

 In thr view of the author this barrier is a barrier mainly or perhaps wholly 

 in tin- sense that, in connection with topography, it indicates certain climatic 

 limits which the species in question do not transgress. 



In relation to local species the region immediately north and south of the 

 Bay has some interest in plant geography. Campanula exigua is found only 

 on the summits of Mt. Diablo. Mt. Tamalpais and Mt. Hamilton. CalochortUS 

 pulchellus is local aboul Mt. Diablo and Streptanthus hispidus in the inner 

 South Coasl Range. other local species are Chorizanthi valida, Arabis 

 breweri and blepharophylla, Tri folium dichotomum and californicum, Psoralen 

 strobilina and douglasii, Astragalus i< ><< r and Arctostaphylos nummularia and 

 audi rsonii. In this connection may be mentioned the genus Ceanothus repre- 

 sented by fourteen Bpecies in the Bay region, of which eight are nearly or quite 

 restricted to the '•'■nt ra I ( loasl Ranges. 



The extensive plains of the Great Valley (the Sacramento and San Joaquin) 



are level and treeless, save for oak groves on restricted areas, mainly along 

 streams, or for a fringe of trees bordering the fixers. The climate is very 



uniform throughout the Greal Valley, but the soil ureas and water content 

 change greatly ami repeatedly, often within short distance. There are. 

 moreover, two distinct seasonal floras, the vernal and the fall, with an inter- 

 vening dry period when the vernal vegetation is killed or dried up, and the seed- 

 lings or perennial herbs which are to flower in the fall are growing slowly. 



The vernal flora of the fertile alluvial plains is rich and varied, a state- 

 ment which refers to areas undisturbed by civilization. The composition of 

 ihis flora is marked by a large Dumber of Bpecies of Ueguminosae, Polemonia- 



