lOA E E. Clements 



east, and the majority constitute societies in the mixed prairie o£ 

 the Great Plains. It appears probable that most of the species 

 of the desert-eastward group originated in the two prairie asso- 

 ciations just mentioned and found their western limit at the 

 desert's edge, though some may well have extended into it or 

 even have arisen during its development. The species that occur 

 in the desert and westward through more or less of cismontane 

 California number 91 ; 67 of these are annuals, 60 of which are 

 found more widely outside the desert. Nearly all the desert- 

 westward perennials appear to be endemic, while the desert- 

 eastward ones are chiefly migrants from the east, as already sug- 

 gested; 7 likewise occur in Mexico. 



SHRUBS 



The total of desert-eastward shrubs is 43, 21 of which extend well 

 to the east into Colorado or Texas. Of the westward group of 20, 

 the large majority are endemic, only 4 being found also in Mex- 

 ico; while of the eastern, 15 occur in Mexico and may well have 

 originated there. 



DESERT ENDEMICS 



The word endemic is used in a general sense to apply to the 

 desert region as a whole, with full recognition of the fact that 

 the limits of the desert are most uncertain in Mexico and Lower 

 California and none too definite in any direction other than west. 

 On this basis, the group comprises 89 species of annuals, 78 

 perennials, and 69 shrubs, the total amounting to 236, in con- 

 trast to the 247 species found in the desert but also extending 

 into the climaxes on either side. Of endemic annuals, the largest 

 numbers per genus are found in Phacelia, Cryptanthe, Gilia, 

 Euphorbia, Langloisia, and Mentzelia; among perennials, Astra- 



