The Plants of the American Desert. 167 



desert in fact is also much riclier in plants than the lowlands of 

 the wadi Arabah. But in the low-lying deserts of southern Cali- 

 fornia I soon convinced myself that this conjecture was incorrect. 

 The depression of the Coahuila desert, 260 feet below tide, was un- 

 fortunately traversed by me at night, from Indio to Tortuga ; but 

 the picture of the landscape which presented itself early next 

 morning at Aztec was almost as rich in vegetation as the Van- 

 horne desert in western Texas, although Aztec lies at an altitude 

 of 500 feet, Vanhorne at 4,500 feet. It is aj^parent from this that 

 topographic altitude is not the cause of the wealth of vegeta- 

 tion in American deserts. It seems, on the contrary, either that 

 the average precij)itation in American deserts is greater, or that 

 American desert plants are better adapted to dry air. Accord- 

 ing to Mr Marcus E. Jones of Salt Lake city, that place has an 

 annual rainfall of about 15-16 inches ; Salt Lake desert about 

 6-10 inches. 



The conductor of the Southern Pacific railwa}^, who has trav- 

 eled through Gila desert dail}^ for many years, told me that there 

 is a rainy season in that desert in July and August. The desert 

 sky, at other times so clear, is then clouded ; there are occasional 

 thunder-storms in the afternoon ; and irregular rain showers fall, 

 their area being so limited that at times the strip receiving rain 

 is only 5 kilometers broad, though the water there covers the 

 ground to a depth of a foot. For the deserts of Texas, according 

 to von Streeruwitz, a mean annual amount of rain cannot be 

 given at all ; for in some cases it does not rain for two years, and 

 again there is a rainfall of two inches in two hours. 



Tlie plants of the American deserts attain no inconsiderable 

 dimensions. In southern Arizona we rode for three hours 

 through a desert in which columnar cactuses half a meter in 

 diameter and 7 meters in height were to be seen by the thou- 

 sand. Never have I witnessed so curious a sight as these huge 

 specimens of Cereus giganteus in such multitudes. The salsula- 

 ceas and artemisias form bushes a meter in height, and their 

 branches are of an arm's thickness ; and, while in the Arabian 

 desert one finds but slight protection against the sun's rays 

 under acacias and tamarisks, in Utah the upper slopes bear 

 shade-giving juniper trees. 



While there exist thus in the conditions of vegetation wide 

 differences, on the other hand there are a series of important 



