886 ADVENTURES IN RADIOISOTOPE RESEARCH 



part of the radioactive phosphorus applied. In the last experiment the 

 first and the second sets of leaves seen in Fig. 1 were ignited after the 

 plant had been growing for 21 days in a culture liquid; the stem was also 

 ignited. 79 per cent of the phosphorus content present in the stem was 

 found to be 'radioactive' phosphorus originating from the culture solu- 

 tion, while the remaining 21 per cent was part of the ordinary phosphorus 

 already present in the plant at the beginning of the experiment. For the 

 lower and the higher leaves the corresponding figures are 71 and 70 per 

 cent respectively 'radioactive' phosphorus and 29 and 30 per cent 

 respectively ordinary phosphorus. 



The practically identical ratios of radioactive phosphorus, originating 

 from the culture liquid, to ordinary phosphorus, in the first and the 

 second sets of leaves clearly indicate that the phosphorus atoms of the 

 leaves are present in a mobile state, and that during the growth of the 

 plant a continuous interchange of phosphorus atoms takes place between 

 the different leaves. The data in the table show also three intermediate 

 stages in the phosphorus uptake of the plant and an increase in the 

 ratio of 'radioactive' to total phosphorus with time. 



The fact that the easy exchangeability already found for lead, which 

 is only incidentally present in plant tissues, has also been ascertained 

 for phosphorus, one of the chief constituents of plants, indicates that we 

 have to do with a general property of plant constitution. To investigate 

 this point closer, it is intended to continue these experiments with other 

 elements. 



Reference 



<i^ G. Hevesy, Biochem. J. 17, 439 (1923). 



■^2) LoHMANN and Jendrasik, Biochem Z. 178, 419 (1926). 



