ggQ ADVENTURES IX RADIOISOTOPE RESEARCH 



removed. The investigation of the assimilation of lead from solutions of 

 different lead content showed that from IQ-* N HNO3 64%, and from 

 10-3 jsf HNO3 practically the same amount, viz. 62% is taken up by 

 the root, when the normality of the lead ions in the solution is lO'e N. 

 From a lO^^ ^ HNO3 solution, a concentration sufficient, in general, 

 to kill the plant, only 26% is assimilated by the root. 



THE DISPLACEMENT OF THE LEAD TAKEN UP BY THE ROOT 



BY OTHER IONS 



Since it has been established that we can displace the lead taken up by 

 the root by other lead atoms, it seemed to be of interest to investigate 

 the ability of other ions to displace the assimilated lead. IQ-^ N solutions 

 were used throughout these experiments. The plant containing lead was 

 placed for 24 hours in the solution under consideration and then both the 

 amount of lead remaining in the plant and the amount displaced into the 

 solution were determined. The results of these experiments are shown 

 in the following table: 



Solution used 



% o£ the lead initially 

 present in the root which 

 remained after treatment 



Lead nitrate (inactive) 



Cupric nitrate 



Cadmium nitrate 34 



5 



Zinc nitrate 



Chromium nitrate 

 Barium nitrate . . . 



38 

 43 

 74 



Sodium nitrate \ '" 



When the reverse solution took place with the help of a 10" ^ N 

 Pb(N03)2 solution, 14% of the originally assimilated lead were still present 

 in the root after 24 hours' treatment. 



Only copper is able to displace lead in a similar degree to lead itselt, 

 all the other cations investigated show an appreciably smaller displacing 



^The extent of the re-solution of the lead taken up by the stem and 

 leaves was not determined. Experiments which are being undertaken on 

 the assimilation of lead by algae will, amongst other things, also serve 



to shed light on this point. * i-rr . 



As is well-known, different ions are assimilated to quite dillerent 



degrees by plants, according to what other ions are present in the culture 



solution The toxicity of individual' types of ions is also arrested by others. 



