TRANSLOCATION 

 IN PLANTS 



CHAPTER I 



THE SIGNIFICANCE OF TRANSLOCATION AND 

 EARLIER OPINIONS AS TO TISSUES INVOLVED 



1. The Importance of Translocation. — The behavior of 

 any given cell or tissue of a plant is largely determined by 

 the kinds and amounts of materials present in that cell or 

 tissue. In the simple types of organisms, especially the 

 filamentous and unicellular forms, the kinds and amounts 

 of materials present in cells are largely determined by the 

 environment, which rather directly influences food manu- 

 facture in that particular cell or the absorption or loss of 

 foods, water, salts, ions, gases, and such. With most of 

 the higher plants, on the other hand, where there are much 

 differentiation and specialization, certain types of materials 

 are absorbed or manufactured in rather restricted tissues 

 or organs. For example, carbohydrate manufacture may 

 be restricted to the leaves, while water absorption may take 

 place chiefly in limited regions of the roots, and salt or ion 

 absorption also may be restricted to certain regions of the 

 roots. There may be considerable specialization even 

 in the salt absorption, whereby much of one element — the 

 nitrogen, for example — may be absorbed chiefly by those 

 roots near the surface, while other ions may be absorbed by 

 the more deeply penetrating roots. Other tissues may 

 serve largely as food-storage tissues, conducting tissues, 

 or as mechanical support. One of the factors that deter- 

 mine the size and conformation of a plant may be the 

 effectiveness of the translocation mechanism, for it is 

 obvious that, to allow for the development of a plant with 



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