32 University of California Publications. [botany 



THE CREST FORMATION. 



Ill examining the flora of any of tlie liigh ridges of San 

 Jacinto Mountain it very soon becomes evident that we are deal- 

 ing with a type of vegetation quite different from that of any of 

 the formations just discussed and, since it cannot be classed with 

 any of these, we have decided to treat it as a distinct group, for 

 which the wmne crest formation has been selected. 



By the crest formation is meant that assemblage of plants, 

 other than trees, found growing on the peaks and I'idges- above 

 7000 feet altitude. The plants of this formation are marked by 

 a strong xerophile tendency brought about by the arid conditions 

 under which they exist, this aridity being due to the low tem- 

 perature, to the rapiditj" with which moisture is conducted to the 

 lower portions of the mountain, to accelerated evaporation caused 

 by diminished atmospheric pressure, and by the drying winds 

 which sweep over those regions. 



The shrnbl>y vegetation is most abundant among the rocks, 

 often springing from fissures in their sides, and is therefore 

 obliged to resort to various devices for collecting and retaining 

 the necessary amount of moisture . Cereocarpus ledifolius accomp- 

 lishes this, in part, l)y a decided reduction in leaf surface and 

 also by the thickening of the leaves and the development of a thick 

 cuticular covering. When growing on the ridges the leaf surface 

 in Holodiscus discolor dumosa is also much reduced. Philadelphus 

 serpyllifolius and Ericameria cuneata have their leaves pro- 

 tected by an external covering, those of the former being silvery 

 canescent beneath, of the latter being covered by a balsamic 

 resin exuded by the leaf. In all these species the stems and 

 twigs are exceedingly tough and wiry. Sometimes the shrubs 

 venture out upon the exposed slopes, where thej- form a low, mat- 

 like growth and connect directly with the chaparral formation of 

 the higher altitudes, the principal species being Casta »ea seni- 

 pervirens, Ceanotlius cordulatus and ArctostapJiylos patula. 



The herbs of the crest formation are almost entirely peren- 

 nials, not a single annual species being at all common on the 

 higher ridges, and are largely confined to somewhat sheltered 

 positions among the rocks where thej' seldom grow to a height 

 of more than a few inches. The roots are more or less woody 



