PLANT ROOT-SOIL INTERACTIONS 



675 



between the two membranes (equilibrium state). But the table shows 

 that when identical strontium and H-membranes were brought into 

 direct contact under a pressure of five kilograms ( see Figure 3 ) , trans- 

 fer of strontium was very rapid. Over 80 per cent of the equilibrium 

 distribution was reached within 48 hours. Contact transfer was vastly 

 superior to solution transfer. Either process, however, should lead to 

 the same equilibrium state. 



If the H-membrane is replaced by live roots, made to touch the 

 strontium membrane by tying them to it with a string ( Figure 4 ) , the 

 transfers, expressed as micrograms of strontium per gram of oven-dry 

 material (Table II), are in favor of contact ( Lopez-Gonzales and 

 Jenny, 1958). 



W 



mM//m 



Figure 3. Rate experiment of solution transfer and contact transfer of stron- 

 tium from a Sr-membrane to a H-membrane. 



Figure 4. Roots tied to a Sr-H-membrane slab accumulate more strontium 

 than roots in an equilibrium solution. 



