882 ADVENTURES IN RADIOISOTOPE RESEARCH 



solution already showed a slight deviation from the geotropic direction, 

 and the leaves situated closest to the root showed signs of withering. 



The toxic action of lead on different plants, such as wheat, radishes, 

 lentils, cabbage, etc., has beeen investigated quite recently by Bonnet 

 [1922]. Just as in the present case, he introduced the plants into 200 cm^ 

 of water after their roots had attained a length of several centimeters. 

 The water contained in solution a definite amount of lead acetate or 

 lead nitrate, and he obtained the following results: 



(1) After the plants had stood in 10~i N solutions of lead salts, lead 

 could readily be detected qualitatively in the root. 



(2) Only traces of lead were found in the stem and in the leaves. 



(3) 10~i N solutions of lead killed, e. g. the wheat plant after 20 days, 

 balsam after two days. 



(4) Mg, Ca and K showed no antagonistic action to lead. 



(5) The greater the dilution, the less lead was taken up by the plant. 

 Our present results confirm these of Bonnet. As regards the first result, 



we were able, thanks to the sensitiveness of the radioactive method, to 

 detect with ease and quantitatively to determine the presence of lead 

 even in the stem and in the leaves. It is interesting to note that Mg, Ca 

 and K, which do not have an antitoxic action, have only a slight capacity 

 for displacing lead, according to the experiments of the present author. In 

 reference to point (5), the radioactive methods enable us to carry out a 

 quantitative investigation of the dependence of the assimilation of lead 

 on the concentration of the solution within wide limits, in which all 

 other methods fail. In this manner, it is found that only 1/500 part of 

 the amount of lead is taken up from a 10"^ N solution as compared 

 with a 10~i Absolution. Those experiments of Bonnet should be mentioned, 

 from which we can see the influence of the assimilation of lead on the 

 growth of plants. He finds the following values: 



PIa7it: The bean. 



Length of root in mm. 



Initially After 1 week After 1 month 



In water 25 100 1000 



In 10-3A^Pb(NO3)2 31 31 32 



Summary 



(1) The assimilation of lead from lead nitrate solutions by Vicia faba has been 

 investigated. A radioactive isotope of lead was mixed with the lead nitrate, and 

 the amount of lead taken up was determined after ignition from the radioactive 

 intensity of the ash of the various parts. This method makes possible the deter- 

 mination of exceedingly small amounts of assimilated lead. 



