WHEAT SEEDLING AND NUTRIEKT SOLUTION 893 



the lapse of some days, they found tliat the radio-phosphorus tak(>n up by 

 the plant was almost uniformly distributed between all phosphorus 

 present in the plant. The migr-ation of radio-phosphorus in the plani 

 was also demonstrated by Biddulph^^\ When placing wheat seedlings 

 containing radio-phosphorus in an inactive culture solution, the radio- 

 phosphorus content of the leaf was found by Brewer and Branley^^^ 

 to have decreased only slightly with time, while the radioactivity of the 

 solution increased slowly through loss of phosphorus from the roots and 

 lower portions of the stalk. 



The author was interested in determining to what extent the uptake 

 of phosphate ions by growing plants is followed by a simultaneous loss of 

 phosphate by the plant. To this purpose he studied the uptake and the 

 release of labelled phosphate ions by wheat seedlings. 



EXPERIMENTAL 



The most direct way to attack the problem outlined above is the growing of 

 seedlings in a nutrient solution containing labelled phosphate and, after the roots 

 are carefully washed, the replacement of the radioactive solution by a non-active 

 one. An exudation of labelled phosphate from the plant should lead to an accu- 

 mulation of radioactive phosphorus in the originally inactive solution. Against 

 this procedure the objection may be raised that the roots of a plant growing in 

 a solution containing labelled phosphate may be covered by active iron phos- 

 phate or another sparingly soluble phosphate, and the activity observed in the 

 originally inactive solution may originate from this deposit and not from the 

 plant proper. Therefore, the author made use of the technique of parted roots. 



Wheat grains are placed for speering on the edge of a glass cuvette which is 

 placed in a beaker. By making use of this technique seedlings with parted roots 

 are obtained. A fortnight old the seedlings are placed in an apparatus composed 

 of two concentric cyUnders. One part of the roots is placed in the inner, the other 

 part in the outer cylinder. The diameter of the inner cylinder is 2.4 cm, that of 

 the outer cyUnder 3.8 cm. Their length is 20 cm. Both cyhnders are filled to a 

 height of 18 cm with nutrient solution of the following composition per liter .^^^ 



0.055 gm KHaPOj 



0.10 gm Mg(N03)2 • 6 HgO 



0.35 gm KNO3 



0.10 gm ferric citrate 



0.5 mgm MnSOi • 4 HgO 



0.25 mgm ZnSOi • 7 H2O 



0.25 mgm H3BO3 



Sodium hydroxide is added until pH — 5.8 is reached. After the lapse of about 

 1 week, for example, labelled phosphate of negligible weight and having an 



<^) O. BiDDULPH, Science 89, 393 (1939). 



<^> A .K. Brewer and A. Branley, Science 91, 269 (1940). 



<3) L. Olsen, L. R. des Travaux du Lab. Carlsberg, 21, 17 (1935). 



