WHEAT SEEDLING AND NUTRIENT SOLUTION 



903 



find the total activity of nucleic acid present in 25 cm^ solution. When 

 carrying out this calculation we assume the weight of the active nucleic 

 acid to be negligible compared with the weight of the 100 mgm inactive 

 nucleic acid added. 



As we, furthermore, analysed only a .^^^ part of the solution, we have 



189 



to multiply the result obtained by ^^. The total activity of the nucleic 

 acid exuded works out to be 129, while a simultaneous analysis of the 

 free phosphate present in the solution indicates a total activity of 716. 

 Thus, 15 per cent of the ^^P which migrated from the roots into the 

 distilled water originate from the ^^P content of nucleic acid exuded. 

 The ratio of free phosphate activity and nucleic acid activity found to be 

 present in the distilled water in which the roots had been placed for 1 

 hour in 3 experiments is seen in Table 14. 



Table 14. — Activity of the Phos- 

 phate Fraction and the Nucleic Acid 

 Fraction Present in the Distilled 

 Water in which Wheat Seedling 

 Roots had been Placed for 1 Hour 



Amount of nucleic acid exuded 



The wheat seedlings used in our experiments were grown almost from 

 the start in labelled solution. The activity of 1 mgm of seedling P can 

 therefore be assumed to be equal to the activity of 1 mgm of exuded 

 nucleic acid phosphorus. In the first set of experiments, the total ac- 

 tivity of the nucleic acid P exuded varied between 0.04 and 0.09 per 

 cent of the total activity of the seedling. The phosphorus content of 

 the dry roots of the seedling (3%) is only 1/3 of the phosphorus content 

 of the nucleic acid; thus, the amount of nucleic acid exuded in the 

 course of 1 hour varies between 0.013 and 0.03 per cent of the dry 

 weight of the roots. Lundegardh and Stenlid have found an exu- 

 dation percentage of 0.5 to 1 per cent in the course of 5 hours 

 or, assuming the amount exuded in the course of 1 hour to be 

 1/5 of the amount exuded in the course of 5 hours, 0.1 to 0.2 per cent 

 per hour. Our values amount to only about ^g of the amount observed 

 by LundegArdh and Stenlid. This difference is, however, to be expect- 

 ed in view of these authors' account. Our experiments were carried out 

 on 2 to 3 months old plants, while LundegArdh and Stenlid per- 



