PREFACE ix 



Miinch also gives a great deal of valuable material relating 

 to translocation. A discussion of his contribution in the 

 present publication is limited almost exclusively to his 

 interpretations of the mechanism of transport. The 

 original should be consulted for other valuable data bearing 

 on translocation, 



I have attempted to give a picture of the present situa- 

 tion regarding translocation and to evaluate the methods 

 that have been used in studying problems relating to it, 

 in the hope that those wishing to carry on with these 

 problems will better appreciate the factors involved and the 

 weaknesses as well as the strong points of the various 

 methods of approach. I also hope this book will serve to 

 make clear its own incompleteness, and, through raising 

 more problems than it settles, serve to stimulate further 

 investigations leading to an advance of our knowledge of 

 these problems and their relation to plant behavior. 



In several instances hypotheses are presented in some 

 detail and criticized in spite of the fact that those who 

 proposed them possibly no longer would uphold their 

 earlier proposals. In several cases I have had no way of 

 knowing whether the hypotheses had been dropped, but 

 even if I had been certain that they had been discarded by 

 their authors, I think it desirable to discuss them critically, 

 especially in view of the fact that the same suggestions are 

 frequently revived or reproposed with varying modifica- 

 tions but often without recognition of the underlying 

 weaknesses. At the same time it is also possible that some 

 of the conclusions which are now seemingly obvious may 

 eventually be shown to be less acceptable than others 

 which are here considered as untenable. I wish to empha- 

 size that the criticisms in no case are directed toward 

 individuals, but in all cases against the methods used or the 

 interpretations of the data. 



I am indebted to my father-in-law, Dr. F. E. Weeks, for 

 his assistance in reading proof. 



Ithaca, New York, O. F. CuRTIS. 



April, 1935. 



