ACKNOWLEDGMENT 



It is a pleasure to express our thanks to the many col- 

 leagues who have aided in one way or another the prepara- 

 tion of this monograph. Dr. J. van Overbeek and Mr. C. L. 

 Schneider have carried out a number of special experiments; 

 Dr. J. Bonner, Dr. J. van Overbeek, and Dr. A. J. Haagen 

 Smit have made numerous valuable suggestions and criti- 

 cisms of the manuscript; and Miss E. M. Wallace has spent 

 much time in the preparation of the drawings. Finally a 

 number of co-workers and students have been kind enough 

 to allow the citation of their unpublished results. In many 

 cases this has made possible the discussion of papers pub- 

 hshed later than the autumn of 1936, although we have made 

 no attempt at completeness beyond this date. Thanks are 

 due to Prof. F. Kogl for the samples of auxin and biotin 

 used in some of the unpublished experiments cited here. 

 Thanks are also due to the authors of a number of papers 

 and the editors of the journals in which they appeared for 

 permission to reproduce figures. The source of these is 

 acknowledged below the figures in each case. 



F. W. Went 

 Kenneth V. Thimann 

 June, 1937 



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