Hoagland 



— 88 — 



Plant Nutrition 



of water passed through a plant, as Kramer points 

 out, this is much greater in a transpiring plant or 

 when liquid is caused to pass through the system by 

 applying suction than when simple exudation is taking 

 place. 



Textfigurb 25. — Time curves for absorption of radio- 

 active sodium and location in shoots and roots of young 

 barley plants. Movement to shoot was delayed in initial 

 period while roots were absorbing sodium, but later sodium 

 moved to the shoot while roots were also still actively ab- 

 sorbing sodium. 



All these experiments of various kinds suggest 

 that salt can move through the root cells or out of 

 them and into the xylem conducting system in the 

 root by a process akin to secretion, at least as an 

 overall effect, based on comparison of the external 

 solution with the exudate. Several questions arise 



