894 



ADVENTURES IN RADIOISOTOPE RESEARCH 



activity of 1 to 10 juCurie is added to the solution of the inner cylinder. The upper- 

 most 2 cm of the cyUnders do not contain liquid, furthermore, the walls of this 

 part of the cyhnders are coated with a layer of paraffin. These measures are taken 

 in order to avoid the creeping of salt along the surface of the cyhnder wall from 

 the active into the inactive solution. The absence of such a disturbing effect was 

 ascertained by adding dyes to the inner solution. No passage of dye could be 

 observed. Furthermore, as discussed on p. 896, the amount of inactive phosphate 

 present in the outer cylinder has a marked influence on the amount of radio- 

 active phosphate which migrates fiom the inner into the outer cylinder. This 

 finding can only be explained by a passage of the labelled phosphorus from the 

 inner solution through the roots into the outer solution, as a creeping of a salt 

 along the surface of the roots can hardlj^ be influenced by small changes in the 

 salt content of the liquid into which the creeping salt ultimately finds its way. 

 To investigate the activity which accumulated in the outer cylinder the liquid 

 is collected through an inveised U tube, slightly acidified with hydrochloride 

 acid and filtered to remove solid particles possibly present. 70 mgm Na2HP04 are 

 then added and the phosphorus is precipitated as ammonium magnesium phos- 

 phate. This precipitate contains the labelled phosphate which had migrated 

 through the "inactive" roots into the outer solution. We denote the roots placed 

 in the inner solution and, thus, growing in a radioactive medium as "active" 

 roots. At the end of the experiment, we extract the acid-soluble phosphorus of 

 the "inactive" roots with 5 p. c. cold trichloroacetic acid. A part of this solution 

 is used for colorimetric determination of its "free" P content, while another part 

 is taken to determine the radioactivity of the "free" P. After the addition of 

 70 mgm Na2HP04, the phosphorus content of the solution is precipitated as ammo- 

 nium magnesium phosphate and is placed under the Gciger counter tube. Another 

 ahquot of the solution is digested and the specific activity of the total acid- 

 soluble P is measured. In another experiment the plant is digested in toto and its 

 P content and its radioactivity are determined as well. 



RESULTS 



The distribution of the total P in the different parts of the plant and 

 the radioactive P (^^P) content of the active and inactive roots is shown 

 in Tables 3 and 4. In some of the seedhngs investigated after the lapse of 



TABLE 3. — Distribution of the Total P in the Different Parts of the Plant 



AND THE ^2P Content of the Roots 



