Lecture 4 



89 — Movement and Distribution 



with regard to this general concept. One of these is : 

 Must salt first be accumulated by root cells to the 

 limit of their capacity for holding salt, before upward 

 movement begins? That this need not be so is shown 

 by an experiment conveniently performed with the 

 aid of radioactive tracers. For a very short period 

 (one or two hours) practically all the absorbed salt 



THE GRADATION OF CATION ACCUMULATION IN 

 ROOTS SHOWN SPECTROGRAPHICALLY. 



SCALE 

 OF CM, 



5-- 



4--- 



3--'- 



Rb. 



LINES 

 7950-0 78110 

 .\A 



ROOT 

 SEGMENT 



1 



O-L 



10 



...SJJ. 



K, 



LINES 

 7699-1 7665J 



ROOT 

 ANATOMY 



■ erJbOOfRMB" 



THICKENED 

 NO PASSAGE 

 CE]XS 



ENOODERMIS 

 COMPIETELY 

 SU8ERISE0 



ENOOOEPMIS 

 SUBERISED WITH 

 PASSAGE CELLS 



"ENDOOERMIS" 

 UNSUBERISED 



VASCULAR 

 DIFFERENTIATION 

 AT 0-5 TPU. 



Textfigure 26. — Accumulation of salt in dif- 

 ferent regions of root. (From Steward, Prevot, 

 and Harrison, 1942). 



(radioactive sodium) was retained by the roots, but 

 following this brief initial phase, the content of radio- 

 active ions continued to increase in the roots and 

 simultaneously upward movement to the shoot oc- 

 curred, while the root cells were still far below the 

 point of salt saturation. 



Another question we might ask, thinking again 

 of the intact plant, is: Assume that the plant is 

 capable of further growth and that the root system 

 does not have access to new supplies of a given ion 



