112 



MINERAL SALTS ABSORPTION IN PLANTS 



mature zones. When salt is supplied to the extreme tip of Viciafaba 

 roots, Brouwer (1954) found in agreement with Wiebe and Kramer, 

 that little or no transport to the more basal zones occurs. On the 

 contrary, even though the root apex absorbs ions directly from the 

 medium, it normally obtains some of its salt supply from more basal 

 regions. Brouwer demonstrated that the relative amounts of salt 

 taken up at different points along the bean root, varies with the rate 

 of concomitant water absorption. When water absorption by the 

 plant was increased, uptake of salt by the extreme tip was unchanged, 

 but that by the more mature zones increased. Some possible 

 explanations of this observation will be given below. 



Table 8. Translocation of Salts from Different Regions of the Barley 

 Root. (Data of Wiebe and Kramer, 1954). 



0- 4 



7-10 



27-30 



57-60 



B. Salt Absorption and Transpiration 



If the movement of salts into roots occurs partly or entirely by 

 mass flow, as early botanists suggested, it should be possible to 

 demonstrate a relationship between the rates of absorption of salts 

 and water. Many experiments have been performed to examine the 

 situation, and the results show that in some cases the two processes 

 are entirely independent, while, in others, salt absorption increases 

 with increased transpiration, to a greater or lesser extent. 



Van den Honert (1933) studied phosphate and water absorption 

 by sugar cane plants growing in well aerated salt solutions. He 

 observed that during the hours of daylight, transpiration was about 

 ten times greater than at night but phosphate absorption was little 

 affected (Fig. 39a; see also Fig. 39b). Such variation in salt 

 absorption as occurred was attributed to fluctuations in temperature. 



