WALTER HOUGH. 449 



the basis of subsistence for an extensive fauna, and also the 

 new-comer man who has pinned much of his faith to natures 

 supply. The region is not in any part a desert in the true 

 sense of the term, which is applied to lands deserted 

 because of an inhibition of life; but it is rather a semi-arid 

 environment, in which a preponderance of desiccative and 

 other factors have restricted and minimized life. These re- 

 strictions are observed in full force among the plants fixed in 

 the earth, and therefore played upon by all the natural forces to 

 which they must adapt themselves by slower changes than are 

 required by higher biotic forms. The characteristic climatic 

 flora is thus xerophytic, or dry-leaved, where the leaves are 

 small with devices for preventing too rapid evaporation, stems 

 contain clorophyl and act when leaves fall away, etc. ; these 

 are adaptations which give some plants the freedom of the 

 desert. Other plants are succulent and spring to quick fruition 

 when rains occur; other plants have perfected water-storing 

 devices in stem, root, and branches, as the cacti, yucca, atri- 

 plex, sarcobatus, etc, and still others can live in soils con- 

 taining an excess of mineral salts. 



Most of the desert plants bear witness to the struggle with sun, 

 wind, rarefied air, and inhospitable soil; thus they present a 

 gnarled, wrinkled, and bizarre appearance, often similating 

 trees dwarfed by the gardeners' art. Unlimited opportunity 

 is here for isolation b} r natural boundaries, which, if not a 

 factor in the origin of species, at least powerfully aids in the 

 preservation of species. 



Much that is observed as to plant life is true also of animal 

 life, giving a fascies by which Merriam's Austral regions may 

 be characterized. 



In all discussions of this environment, little or no attention 

 has been paid to the effects of light, which is here at its maxi- 

 mum. Without entering into detail as to the physiological 

 sequelae of light from other parts of the spectrum, the rays 

 from the violet end may be considered. These rays affect all 

 life submitted to them in a harmful manner by checking or 

 prohibiting cell growth or metabolism. It will be found 

 that many of the protective features of xerophytic plants and 



