EDITOR'S NOTE TO THE SECOND AMERICAN EDITION 



In this, the second American edition of Palladin's book, a few typo- 

 graphical and other errors that have come to the editor's attention have 

 been corrected. In a very few cases the wording of the text has been somewhat 

 improved, especially where the old wording was not quite clear. Several new 

 notes by the editor have been added, notably in Part II, Chapters V and VI. 

 While a small number of additional references to the literature have been 

 inserted, no attempt has generally been made to enlarge the scope or increase 

 the number of the citations. The text and notes are generally the same as in 

 the first Edition. The editor is glad to acknowledge valuable assistance re- 

 ceived from Dr. Sam F. Trelease, and also to express his thanks to those readers 

 who have called his attention to errors occurring in the first Edition. The 

 publishers have assumed the responsibility for the index. 



One new feature has been added, in the form of a summary for each chapter. 

 In preparing the- summaries it has been attempted to present a succinct but 

 rather complete statement of the main features dealt with in the respective 

 chapters, with the idea that these resumes may be useful to the student, espe- 

 cially in reviewing the subject. It is suggested, also, that the summary of a 

 chapter may be read with profit before reading the chapter itself, the summary 

 thus serving as a sort of general background for the more detailed information 

 gained by perusing the fuller presentation. In some cases new material has 

 been introduced into the summaries, mainly to clear up a few vague transitions 

 from one topic to another that occur in the text, and generally to help the stu- 

 dent gain a logical and consistent view-point for the subject as a whole. The 

 editor is alone responsible for the summaries. 



The Desert Laboratory, 

 Tucson, Arizona, 

 July 15, 1922. 



xin 



