THE BROAD-SCLEROPHYLL VEGETATION OF CALIFORNIA. 15 



is so evident in the various taxonomic treatments of certain genera 

 is itself evidence after a fashion. The genera Ceanothus and Arcto- 

 staphylos are classic examples. In both, the number of species 

 proposed has been very large. Many of these fall into definite 

 groups having close relationship within themselves, and by some 

 authors these groups are treated as single variable species. A case 

 in point is the group-species known commonly as Arctostaphylos 

 tomentosa. From this Miss Eastwood has segregated three forms, 

 all of which grow upon Mount Tamalpais; Abrams refers all to 

 A. tomentosa. Howell has described 7 from southwestern Oregon, 

 which Abrams reduces to synonymy. In Ceanothus several groups 

 of closely related forms or species might be noted (Brandegee, 10), 

 and in Rhamnus and Garrya the structure is similar, but on a smaller 

 scale. It is evident that variation and hybridization are rampant 

 among certain genera of the California sclerophylls. It is impossible 

 to locate accurately the geographical area where these processes 

 are most active, further than to state that they are less evident in 

 the Sierras than in the Coast Ranges and southern California. 



LOCATION OF MAXIMUM SIZE OF INDIVIDUALS. 



In the case of the 9 broad-sclerophyll trees decision is easy; 4 of 

 them, Myrica californica, Quercus agrifolia, Q. chrysolepis, and 

 Q. wislizeni, attain their largest size in the central Coast Ranges, 

 and the last two (according to Sargent) also in the central Sierras; 

 4 more, Castanopsis chrysophylla, Pasania densiflora, U?nbellularia 

 californica, and Arbutus menziesii, make their best growth in north- 

 western California. Quercus engelmanni is confined to southern 

 and Lower California. As to the chaparral shrubs, data are scanty 

 and unsatisfactory, especially because fire so commonly brings the 

 shoots to an untimely end. As to the most important single species, 

 Adenostoma fasciculatum, the greatest average size that I have seen 

 was in San Benito County, in the south Coast Ranges. Other 

 species, ordinarily shrubs, attain respectable tree size in the same 

 general region, e. g., Heteromeles arbutifolia and Prunus ilicifolia 

 in the vicinity of Palo Alto. The very general statement may be 

 made that the broad-sclerophylls attain their greatest size in the 

 coastal region — the trees in the north and the shrubs in the south. 



LOCATION OF LEAST DEPENDENCE UPON A RESTRICTED 



HABITAT. 



In southern California we find the broad-sclerophylls least con- 

 fined in this respect. East of San Diego the chaparral (mainly 

 Adenostoma fasciculatum) covers the gently sloping mesas, and is 

 solid on all exposures of the lower Cuyamaca Mountains (plate 11a). 

 The same is true, where environmental conditions are undisturbed, 

 in certain parts of the Los Angeles and San Bernardino Valleys and 



