Viii PREFACE 



findings, of the commonly accepted interpretations, as 

 well as the investigations of Madam Birch-Hirschfeld and 

 Professor Dixon led to a realization of the fact that the 

 evidence bearing on translocation was incomplete and that 

 much of that which has been published is directly contra- 

 dictory. It was soon apparent that those favoring the 

 xylem as the tissue chiefly concerned in solute transport 

 based their conclusions almost exclusively on experiments 

 involving movement of materials, either naturally present 

 or introduced, after the conducting tissues were opened by 

 cutting, while those favoring the phloem tissues as chiefly 

 concerned in transport downward or upward or in both 

 directions based their conclusion chiefly on ringing experi- 

 ments. Since several writers apparently failed to recognize 

 the relative significance of the different methods used and 

 since no works have been published which bring together 

 the various viewpoints and interpretations relating to 

 solute translocation, I have attempted to bring some of this 

 material together in the present publication. 



No attempt has been made to refer to all papers dealing 

 with translocation problems or in any sense to give a 

 complete historical review of the subject. It will be clearly 

 evident to the reader that a great deal of space has been 

 devoted to a discussion of my own contributions. This 

 is largely due to the fact that these contributions lead to 

 an interpretation that has not been generally recognized 

 or accepted. Perhaps insufficient space has been given 

 to a presentation of the more recent findings of Mason and 

 Maskell. This is partly due to the fact that the writing 

 of several chapters of this book was nearly completed at 

 the time their papers appeared and partly to the fact that 

 many of their experiments repeat, under somewhat modified 

 conditions, the experiments I had previously reported, and 

 lead to the same conclusions. Where their data or interpre- 

 tations differ from mine, I have discussed them at length. 

 Their publications are really outstanding contributions 

 to the subject and no one interested in translocation should 

 fail to read their original papers. The extensive work of 



