186 J. C. BLUMER 



is thus suggested by these three species between the hot and dark 

 character of their habitat and their yellow color. 



The desert shrub possessing the largest leaf is the compositous, 

 monoecious half-shrub Franseria dumosa, which is found only on 

 the larger washes and rarely on the well sheltered north side of 

 cliffs. Aside from the cacti and an occasional Ephedra and Koe- 

 berlinia, which are leafless, the plant having the smallest leaves 

 is Parkinsonia microphylla: it is the most abundant of the trees 

 of the real desert and enjoys the most general distribution. The 

 contrast between these forms is readily apparent. 



The bulk of the winter annual vegetation, just coming into 

 bloom at that time, belonged to eight species of Cruciferae and five 

 species of Borraginaceae. These are well known to be predomi- 

 nantly circumpolar families, i. e., they are adapted to low tempera- 

 tures both in season and in geographic distribution. 



The Cababi hills and the extremely rocky foothills of the Como- 

 babi mountains bear a large number and variety of shrubs, cacti 

 and smaller perenr ials. The flora of such rocky hillsides is always 

 richer in species than that of the deeper soil of the alluvial and 

 rockless detrital plains adjacent. The winter annuals, always 

 more abundant on northern than on southern slopes, in the present 

 perhaps somewhat unfavorable season are confined to the shadiest 

 and moistest portions of strictly northern slopes. In strong con- 

 trast to the dark rock and soil and the grassless vegetation, stands 

 out the gregarious and formidably armed Bigelow cholla, render- 

 ing many hillsides almost white at a distance and scarcely travers- 

 able when at hand. 



The country on the top of the southern part of the Comobabi 

 mountains is by no means as forbidding as is suggested by the 

 foothills. The geologic formation is older, traversed by dykes in 

 a northwest-southeast direction. There is much undulating, 

 grassy country, the grasses and herbs being mostly perennials, but 

 with a considerable number of common annuals amongst them. 

 The country is dotted with shrubs, the most prevalent being Acacia 

 greggii. Prosopis, Condalia lycioides, and Lycium fremontii are pres- 

 ent occasionally. A few scattering giant cacti reach the south sides 

 of the highest summits, and Fouquieria splendens and Jatropha 



