PREFACE 



If one reads the literature dealing with problems relating 

 to the translocation of solutes within plants, it soon becomes 

 apparent that, relative to the importance of the subject, 

 very little experimental evidence is available to which one 

 can confidently turn for information and guidance. In 

 fact, the available evidence has led to flatly contradictory 

 conclusions. These contradictions obtain even with refer- 

 ence to such fundamental points as the tissues chiefly 

 concerned in transport, and the mechanism of transport. 

 One or both of these questions must be solved before any 

 real progress can be made in an understanding of solute 

 movement, or of the factors influencing the direction of 

 movement, the rate of movement, or the final distribution 

 of the materials. Any satisfactory explanation of the 

 behavior of those plants which are differentiated into tissues 

 and organs haidng differences in abilities to produce or 

 absorb special substances, as for example differentiation 

 into leaves which carry on photosynthesis and roots which 

 absorb soil solutes or water, must involve also an explana- 

 tion of conditions determining translocation of solutes 

 from one part to another, because interchange of special 

 solutes or their distribution within an organism has a 

 profound effect upon its behavior. No higher plant could 

 have developed or could even continue to exist without an 

 effective conducting tissue and transport mechanism. 



Despite the importance of the subject, very few texts of 

 general botany, or even of plant physiology, devote more 

 than a paragraph or two to the subject of translocation, 

 while many refer to the process very indirectly or only 

 incidentally in the discussion of some other topic. My own 

 investigations led me to disagree with some of the generally 

 accepted interpretations regarding translocation and raised 

 several interesting problems. A consideration of these 



