No. 448-] NOTES AND LITERATURE. 329 



time of the rains a variety of annual vegetation may spring up. 

 From Tucson the authors proceeded to the Sonora region of Mexico, 

 stopping at Nogales, and thence to Torres. Various interesting forms 

 are described from this region, among the most remarkable of which 

 is a cucurbitaceous tendril bearing plant, Ibervillea sonorae, whose 

 root and stem base are enormously swollen for water storage, and 

 a tree-like morning-glory {Ipomoea arborescens), which grows twenty 

 to thirty feet high. At Guaymas on the Gulf of California, a curious 

 mixture of plant forms was observed, the beach is lined with man- 

 groves, while close to them were the strictly xerophytic Cacti, for as 

 far as rainfall is concerned Guaymas is even more arid than Torres. 



In the Colorado desert of California several types of vegetation are 

 found, due to differences in the soils ; there are the gravel hills, the 

 alkali, and salt flats, the two last named showing a very restricted 

 growth of vegetation. The fan-leaved palm, Neowashingtonia filifera 

 is native to the eastern foot hills of the San Bernardino mountains 

 which lie in the Colorado desert district. They grow in groves form- 

 ing miniature oases where a clayey soil, from which oozes what water 

 has come from the hills, crops out to the surface. Northward lies 

 the Mohave desert where grows Yucca arborescens and Jiiniperus 

 californica, while in the lower altitudes the creosote bush (Covillea 

 tridentata), is the prevailing woody plant. From the Mohave the 

 authors proceeded to the grand canyon of the Colorado, but were 

 disappointed to find that the number of woody desert plants found 

 along the canyon's sides were comparatively small. This they ascribe 

 to the narrowness of the canyon which probably induces abnormal 



Following the account of the actual journey is a consideration of 

 the characteristics of deserts in general and of North American 

 deserts in particular. Meteorological tables are given, showing the 

 rain-fall for various localities from Oregon, to San Luis Potosi m 

 Mexico. One table of especial interest gives the mean annual pre- 

 cipitation as compared with the estimated annual evaporation. The 

 ratio in favor of the evaporation is anywhere from 6 : i to 35.2 : i. It 

 is also pointed out that the distribution of rain fall during the year is 

 of great importance in determining the character of the flora. 

 Another factor in the production of desert conditions which cannot 

 be disregarded is the soil constituents, a fact that is illustrated by the 

 conditions which exist in the gypsum containing White Sands of 

 Tularosa, the " white alkali " which is mainly sodium sulphate and 

 the "black alkali" where sodium chloride and sodium bicarbonate 

 are the chief soluble constituents. 



