BOOKS AND CURRENT LITERATURE 307 



the inner base of the Atlas ranges to 4.7 cm. (1.85 in.) at El Golea, in 

 the heart of the Sahara. The annual evaporation is nearly 400 cm. 

 (157 in.), as averaged for three stations in the Sahara. The annual 

 ratio of rainfall to evaporation is 1 : 46.5 for the three desert localities. 

 The results of an extended examination of the root systems of char- 

 acteristic plants of the Algerian desert is given. The soils vary in 

 depth as well as in texture, and the deep soils are found to support 

 the densest plant populations, at least where grazing does not inter- 

 fere. Some of the desert shrubs are found to have a definite type of 

 root system*, with a long tap, and such plants are restricted in 

 distribution by the depth of the soil. Other plants have variable or 

 generalised root systems and are more ubiquitous in occurrence. The 

 absence of succulents and the general scantiness of the vegetation ren- 

 der the Algerian desert verj^ unlike the deserts of southern Arizona and 

 western Texas. The relation of root types to soil conditions is, how- 

 ever, very similar in Africa and America. — F. S. 



