ABSORPTION OF LEAD BY PLANTS 883 



(2) Whereas 0.3% of the lead is taken up by the root from 200 cm^ of a 10""i N 

 lead nitrate solution in the course of 24 hours, 60% of the lead content of a 10"* N 

 solution is taken up in the same time. The leaves show a lead content of only a 

 few hundredths or thousandlhs of 1% of Ihe amount of lead present in the solution. 



(3) The assimilated (radioactive) lead can be displaced by introduction of the 

 plant containing lead into another lead solution, whereby inactive lead atoms 

 now take the place of the radioactive ones. From this it follows that most of the 

 lead is not combined with cuirbon within the plant, but that it exists in the form 

 of a dissociable salt which is solubl(> with difficulty. 



(4) Even after 24 hovirs, a 10~i iV solution of a lead salt produces toxic effects 

 on the plant, whilst more dilute solutions do not. Lead belongs to the least poison- 

 ous of the heavv metals. 



References 



Arrhenius (1922) J. Gen. Phys. 5, 87. 



Bonnet (1922) Compt. Rend. Acad. Sci. 174, 488. 



Hevesy and Zechmeister (1920) Ber. dtsch. chem. Ges. 53, 410. 



Knop (1885) Ber. sacks. Ges. 51. 



Lavison (1911) Ann. Sci. Nat. Bot. 14. 



Nolle, Bassler and Will (1884) Landw. Versuchsamt 30, 382. 



OsTERHOUT (1912) Science 35, 112. 



Phillips (1883) Bot. Centmlh. 13, 364. 



Strasburger (1891) Histologische Beitrdge 3, 607. 



56* 



