Hoagland — 94 — Plant Nutrition 



salt. The sensitivity of the method makes feasible 

 tracing the movement of an inorganic solute even 

 when the time interval is very short. Thus secondary 

 effects occurring over longer periods are largely pre- 

 cluded. Stout and Hoagland (1939) performed a 

 series of experiments with radioactive tracers of phos- 

 phate, bromide, and potassium ions on several species 

 of plants with the hope of gaining some rather clear 

 cut data on the path of upward translocation of these 

 ions. 



The conclusion was that the upward movement of 

 the solutes in the wood was far more rapid than in 

 the bark, but that a rapid lateral transfer of solute 

 from wood to bark took place whenever the two 

 tissues were in contact. Thus the separation and 

 analysis of the tissues sometime after absorption of 

 the solute could not yield correct conclusions regard- 

 ing the path of upward movement. As the salt moves 

 upward it is rapidly accumulated on the way by met- 

 abolically active living cells. Extensive experiments 

 in California by BENNETT* on the movement of radio- 

 active potassium in prune trees girdled in various 

 ways lead to similar general conclusions. 



Other Effects Associated with Conditions Influ- 

 encing Transpiration : — Another set of experiments 

 in the laboratory was designed to test the effects pro- 

 duced by a highly humid atmosphere on absorption 

 and upward movement of indicator elements in plants 

 different in type from the barley plants already de- 

 scribed. The purpose was to eliminate or to reduce 

 transpiration to the lowest possible value by placing 

 the plants in illuminated chambers with an atmosphere 

 saturated with water vapor maintained by spraying 

 water from fine nozzles. 



In one experiment large squash plants were used 

 in which the root pressure developed might not suffice 



*In course of publication. 



