44 CALIFORNIA ACADEMY OF SCIENCES [Proc. 4th Ser. 



Axiomatic is the tenet that accurate systematic determina- 

 tion of species must be the foundation for any distributional 

 study. 



For life-zone maps relating to California, either for the 

 entire state or for particular areas within the state, the fol- 

 lowing- papers should be consulted: C. Hart Merriam, 1898; 

 C. Hart Merriam, 1899; H. M. Hall, 1902; J. Grinnell, 1908; 

 A. O. U. Committee, 1910; J. Grinnell, 1913; J. Grinnell 

 and H. S. Swarth, 1913; J. Grinnell, 1915. Useful dis- 

 cussions of the life-zone system of distributional treatment 

 of plants and animals will be found in the following papers : 

 C. Hart Merriam, 1899; H. M. Hall, 1902; J. Grinnell, 1915. 

 (For full titles of all these papers, see list of "Literature 

 Cited" on a subsequent page of the present contribution.) 



LISTS OF LIFE-ZONE INDICATORS 

 LOWER SONORAN ZONE 



Species closely restricted to this zone, and particularly characteristic of it, are 

 marked with a star (*). Species marked U occur also in the Upper Sonoran Zone. 



Plants 



Ephedra californica Wats. 

 Pleuraphis rigida Thurb.* 

 Tridens pulchellus (H. B. K.) Hitchc. 

 Washingtonia filifera Wendl.* 

 Hesperocallis undulatus Wats.* 

 Yucca brevifolia Engelm. U 

 Yucca mohavensis Sarg. 

 Agave deserti Engelm. 

 Anemopsis californica Hook. U 

 Phoradendron californicum Nutt. 

 Rumex hymenosepalus Torr. 

 Atriplex hymenelytra (Torr.) Wats. 

 Atriplex lentiformis (Torr.) Wats.* 

 Spirostachys occidentalis Wats. 

 Mirabilis froebellii Greene 

 Lepidium fremontii Wats. 

 Isomeris arborea Nutt. U 

 Crossosoma bigelovii Wats. 



