ACKNOWLEDGMENTS 



To one who considers that personal friendship and generosity 

 in sharing the fruits of scholarship are among the very best things 

 of life, it gives great pleasure to acknowledge indebtedness to the 

 many savants who have contributed of their knowledge or store of 

 illustrations to the benefit of this work. They must not, however, 

 be held responsible for any shortcomings it may have — such as, 

 perhaps, in some views, omission of discussion of certain con- 

 troversial issues which seemed best by-passed at least at the time 

 of writing. Notable among these are Dr. C. W. Thornthwaite's 

 work on evapotranspiration and the classification of climates. 

 Professor Eric Hulten's views on the history of arctic and boreal 

 species, and various ideas about the places of origin of plant forms 

 and the possibilities of their being multiple (polytopic). 



The book owes its inception to the foresight of Dr. George H. T. 

 Kimble, who, when Director of the American Geographical Society, 

 was instrumental in my being invited and generously commissioned 

 to prepare it for a new series of ' readers ' on geographical subjects. 



Early on, the general plan was improved from time to time 

 following discussion with colleagues at Oxford, Yale, and Harvard 

 Universities, in its near-final form being approved by a seminar at the 

 last-named. The plan also derived benefit from many individuals 

 elsewhere ; among these my former teacher and chief, the late 

 Professor Sir Arthur G. Tansley, and my former pupils, Professor 

 John H. Burnett and Dr. John Warren Wilson, were particularly 

 helpful. Yet others who made valuable suggestions, most of which 

 were gladly adopted, include Professor Hugh M. Raup of Harvard 

 University, Professor Paul B. Sears of Yale University, Professor 

 Joseph Ewan of Tulane University, and Drs. Raymond F. Fosberg 

 and Henry K. Svenson, both of Washington, D.C. The then 

 Directors of the two main botanical gardens of the United Kingdom, 

 the late Professor Sir William Wright Smith of Edinburgh and Sir 

 Edward J. Salisbury of Kew, also gave freely of their advice, as did 

 the former Director of the New York Botanical Garden and of the 

 Arnold Arboretum, the late Professor Elmer D. Merrill. The book, 

 moreover, derives much from the able (and direct) teaching of two 



