ORGANIC CONSTITUENTS OF THE SOIL SOLUTION 99 



Finally, although less work has been done in this direction 

 with higher plants than with other organisms, it is now recog- 

 nized as a general law of all living organisms that they function 

 less readily as the products of their activities accumulate. 1 

 These products may, however, be inimical, neutral or even stimu- 

 lating to other organisms. 



This problem has been investigated critically by direct experi- 



1 It may not be amiss to point out here that this general law holds 

 for all dynamic phenomena. In chemistry, for instance, the general law 

 is well recognized that the rate of reaction diminishes with increase in 

 the active mass of the reaction products. It can be shown that the prin- 

 ciple applies to plant growth. Young plants will withdraw potassium 

 more rapidly than chlorine from solutions of potassium chloride; that is, 

 the solution soon contains free hydrochloric acid. Conversely the plants 

 cause a solution of sodium nitrate to become alkaline. Therefore, if the 

 above principle holds, then the initial addition of small amounts of 

 hydrochloric acid to a solution of potassium chloride should slow up the 

 absorption of potassium by seedling wheat plants, or the addition of 

 sodium hydroxide the absorption of nitrogen from a solution of sodium 

 nitrate. Mr. J. J. Skinner has tested this idea with the following results, 

 growing carefully selected wheat seedlings, for 3 days in solutions of 

 pure potassium chloride, solutions of potassium chloride containing initially 

 enough excess of hydrochloric acid to be of an N/5,ooo concentration 

 with respect to the acid, solutions of sodium nitrate, and solutions of 

 sodium nitrate containing initially an excess of sodium hydroxide. 



Solutions of KC1 containing 80 p. p. m. KO. 

 I K 2 O absorbed 40.0 p. p. m. 

 2, K 2 O absorbed 40.0 p. p. m. 



3 K,O absorbed 36.3 p. p. m. 



Solutions of KC1 (80 p. p. m. KaO) and HC1 (N/5,ooo). 



4 K 2 O absorbed 26.7 p. p. m. 



5 KaO absorbed 29.5 p. p. m. 



6 KaO absorbed 26.7 p. p. m. 



Solutions of NaNO 3 containing 80 p. p. m. NH 8 . 



7 NH 3 absorbed 30.2 p. p. m. 



8 NH 8 absorbed 30.2 p. p. m. 



9 NH 3 absorbed 32.5 p. p. m. 



Solutions of NaNO, (80 p. p. m. NH 3 ) and NaOH (N/5,ooo). 



10 NH 3 absorbed 27.8 p. p. m. 



11 NH 3 absorbed 34.3 p. p. m. 



12 NH 3 absorbed 27.8 p. p. m. 



