vi PREFACE 



regions, and numerous special monographs and papers dealing 

 with plant distribution by American botanists and those of other 

 countries. The important series of monographs "Die Vegetation 

 der Erde" has been found especially helpful, and the well-known 

 "Naturliche Pflanzenfamilien " of Engler and Prantl has been 

 frequently consulted. 



A considerable number of important photographs which have 

 added materially to the value of the book, were furnished through 

 the courtesy of colleagues and others, to all of whom the writer 

 is greatly indebted and would express his sincere thanks. Due 

 credit is given in each case. 



It is hoped that the volume will not prove too technical to be 

 of value to the general reader interested in the subject of plant 

 distribution; but the writer has tried to make it sufficiently de- 

 tailed to be useful, also, as a book of reference for botanists, or 

 as a text in classes studying the general subject of plant geography. 



Douglas Houghton Campbell. 



Stanford University, 

 February, 1926. 



