Originally published in Nature, 137, 65 (1936). 



90. ATOMIC DYNAMICS OF PLANT GROWTH 



G. Hevesy, K. Linderstk0m-Lang and C. Olsen 

 From the Institute of Theoretical Physics and the Carlsberg Laboratories of 



Copenhagen 



Some years ago, one of us investigated the circulation of lead in plants 

 using a radioactive lead isotope as indicator. Recent developments in 

 nuclear chemistry make it possible to prepare radioactive isotopes of 

 several of the light elements which, in contrast with lead, are the chief 

 components of plant tissue. This enables us to investigate whether the 

 atoms building up the tissues of the plant remain in their places or 

 migrate during growth to other parts of the plant. 



Let us, for example, consider the phosphorus atoms present in the 

 lowest leaf of a maize plant; during the growth of the plant a second 

 leaf will appear and the question to be decided is whether the first 

 leaf gives up its own phosphorus atoms partly or wholly to build up the 

 second leaf, or whether the phosphorus atoms carried up through the 

 'stem' (in reality undeveloped leaves) from the soil or from a culture 

 solution are responsible for the formation of the second leaf. To solve 

 this problem, the method of isotopic (radioactive) indicators can be 

 applied using as indicator the radioactive isotope of phosphorus ^ap^^^ 

 which has a half-life of about a fortnight. We prepared this isotope by 

 bombarding carbon disulphide, in which a few milligrams of phosphorus 

 were dissolved, with neutrons from a mixture of beryllium and a few- 

 hundred millicuries of radon, distilled off the carbon disulphide, oxidized 

 the remaining phosphorus, and converted the phosphoric acid formed 

 into sodium phosphate. 



Small maize plants were grown for ten days in a culture solution of the 

 usual composition and were then transferred to another culture solution 

 in which the ordinary phosphorus was replaced by an equivalent amount 

 of 'radioactive' phosphorus. Since the phosphorus isotopes cannot be 

 separated by chemical processes, it follows that if, for example, one per 

 cent of the radioactivity added to the culture liquid is found to be 

 present in any part of the plant, we can conclude that one per cent 

 of the those phosphorus atoms which were present initially in the culture 

 solution are present also in that part of the plant. We will call the last 

 mentioned phosphorus for the sake of brevity 'radioactive phosphorus'. 



