WHEAT SEEDLING AND NUTRIENT SOLUTION 901 



of magnesium ammonium phosphate cannot be made responsible for 

 the result obtained. 



The distilled water was redistilled from a glass vessel and thus was free 

 from traces of heavy metals, the presence of which can thus not be 

 made responsible for the behaviour of the roots. The result obtained 

 suggests therefore that distilled water already in experiments taking 1 

 hour only influences the permeability of the root cells. The distilled water, 

 while influencing the phosphate permeability of the root cells, may not 

 necessarily produce an injury of the cells. Nitella cells kept in distiUod 

 water for 3 days, for example, were found to lose their irritability and 

 their characteristic behaviour with potassium, l)ut no sign of injury 

 was observed and such cells w-ere found to live indefinitely when trans- 

 ferred to pond water(^). 



Exudation of phosphorus compounds by the roots 



In our considerations we started from the assumption that labelled 

 phosphate found in the "inactive" nutrient solution containing phosphate 

 is due mainly to an interchange between the phosphate ions present 

 in the plant and those present in the nutrient solution. This assumption 

 is not quite correct, as LundegArdh^-) and his collaborators have shown 

 that living roots always exude small amounts of organic substances. 

 These authors observed that the said substances contained phosphorus. 

 LuNDEGARDHandSTENLiD^^) experimented with roots of young seedlings, 

 2—4 days old. The roots were cut off from the seeds and submersed in 

 aerated distilled water or aerated dilute solutions of salts or mineral 

 acids. Most of their experiments were carried out in distilled water only. 

 They found that 8 per cent of the exudate of wheat, roots had been com- 

 posed of nucleotides, the amount being determined both spectrochemi- 

 cally and by making use of the benzidine test. The amount of nucleoti- 

 des exuded in the course of 5 hours was estimated by them to corre- 

 spond to 0.5—1 per cent of the total dry weight of the roots (the tips 

 found to exude 2 — 4%). The decrease in exudation after 5 hours was 

 interpreted as being probably due to a cessation of growth of the seed- 

 lings after that time. 



In view of these results, we measured the amount of labelled nucleic 

 acid exuded in our experiments and determined the percentage of 

 32p migrated from the roots into the nutrient solution which could be 



(i)S. E. Hill, Proc. Soc. Exp. Med. 32, 413 (1934 • 1935). 



^2) H. LuNDEGARDH, Die Nahrungsaufnahme der Pflanze, Jena (1932); H. 

 LuNDEGARDH, H. BuBSTROM and E. Rennfelt, Svensk Bot. Tidsskr. 26, 271 

 (1932); H. BuBSTROM, I.e. 28, 157 (1934). 



(^^H. LuNDEGABDH and G. Stenlid, Kungl. Svenska Vetensk. Akad. Ark. /. 

 Bot. 31 A, No. 10 (1944). 



