PHOSPHORUS ATOMS IN PLANTS 



889 



for exchange to occur between the labelled phosphorus in the leaf and 

 the normal phosphorus in the solution. No labelled phosphorus could, 

 however, be found in the nutritive solution. 



In another set of experiments we placed cut leaves of sunflowers, 

 grow^n in a normal nutritive solution, in labelled solution for 48 hours; 

 in all the cases investigated an uptake of a few per cent of the labelled 



Table 2. — Maize 



Table 3. — Pea 



phosphorus atoms into the cut leaf was found. As was to be expected, 

 a cut leaf takes up not only the solvent but also the solute from the 

 solution in which it has been immersed. 



Finally, we would like to mention some experiments carried out with 

 seeds. Two different series of experiments were carried out, one with 

 maize seeds, the other with those of the pea. In both cases the seeds were 

 germinated until rootlets 2—3 cm long were formed. Then the seeds were 

 placed in small flasks with the rootlets dipping into a nutritive solution 

 containing labelled phosphorus. In the case of the maize seeds (Tal)le 2) 

 the germ and endosperm were removed after the lapse of 4— 14 days and 

 analysed separately. While the germ was found to contain an appreci- 

 able amount of labelled phosphorus taken up from the nutritive solution, 

 the endosperm did not contain the slightest trace; this shows that 

 no exchange takes place between the phosphorus atoms of the germ and 



