CONTENTS. 



Page 



Introduction 5 



Soil studies 7 



General character of the soil 7 



Water content of the soil in the dry season 8 



Permeability of the soil to water and rate of downward movement 12 



Retaining power of the soil for percolating water 14 



Power of the soil to raise water from lower levels 17 



Resistance offered by the soil to water absorption by roots 19 



Supply of water to the soil 22 



Atmosphere studies 24 



General problem 24 



Evaporation from a water surface a new form of evaporimeter 24 



Evaporation from the soil 34 



Plant studies 38 



Introductory 38 



Water requirement for germination 40 



Transpiration of desert plants 41 



The general problem 41 



Some measurements of transpiration; a new method for studying the 



physiological regulation of this function 42 



Generalizations from the experiments 63 



Water requirement of certain desert plants 65 



Osmotic pressure of cactus juices 70 



Conclusion 72 



Summary 75 



Literature cited 77 



3 



