X PREFACE TO THE GERMAN EDITION 



five years. He has endeavored to present objectively the views 

 of various investigators, to distinguish as clearly as possible 

 between experimentally founded fact and more or less hypo- 

 thetical views. Particular attention is given to the fundamentals 

 of the growth-substance theory — and the author hopes, therefore, 

 that his work will be useful to those carrying on growth-substance 



research. 



P. BoYSEN Jensen. 



Laboratory of Plant Physiology, 

 University of Copenhagen. 



