WHEAT SEEDLING AND NUTRIENT SOLUTION 



899 



Table 10. — Passage of Phosphorus from the Solution through the Roots 

 INTO THE Plant in the Course of 1 Day. Average temperature 22° C 



Thus, 68 y passed through the roots in upward movement during 

 1 day. As we found under the same conditions 12.6 y of P to have moved 

 from the roots into the solution, we have to conclude that for about 6 

 phosphorus atoms taken up by the roots 1 phosphorus atom moves in 

 opposite direction, viz. from the roots into the nutrient solution. This 

 result was found from a nutrient solution containing 0.4 millimol. 

 phosphorus per liter. By increasing the phosphate concentration of the 

 "inactive" solution, the passage of phosphate from the roots into the 

 solution increases; when decreasing the phosphate concentration the 

 passage decreases, as seen in Table 11. The latter result we should expect 

 to obtain for an interchange process in contrast to a dissolution process. 

 In the case of an interchange process, the probability of the removal of 

 an active P atom by an inactive one increases when the concentration 

 of the inactive P atoms is increased. 



Table 11. — Removal of Labelled 

 Phosphate from the Roots of Wheat Seed- 

 lings IN Nutrient Solutions of Different 

 Phosphorus Contents in the Course of 

 1 Hour 



Ratio of the removal of labelled phosphate from the roots 

 by a nutrient solution containing 



4 and 0.16 millimol. P per 

 liter, respectively 



0.4 and millimol. P per liter, 



respectively 





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