XVI PREFACE. 



The studies here reported were carried out under the auspices 

 of the Department of Botanical Research of the Carnegie Institution 

 of Washington. They were begun when both the authors were located 

 at the Desert Laboratory. We are greatly indebted to many persons 

 who collaborated and assisted in various ways. Especially should be 

 mentioned Grace J. Flanders, who carried out most of the climato- 

 logical computations upon which the work rests and who assisted 

 very much in the preparation of the climatic charts. Others who 

 helped with computations are J. W. Shive and H. E. Pulling. The 

 cooperators in our series of evaporation observations, whose names 

 are given in table 13, should also be mentioned here. It is interesting 

 and significant to remark that this series of studies, in which these 

 individuals so kindly assisted, formed the point of departure from 

 which the whole study, as here presented, has been developed. 



