84 Journal of Agricultural Research voi. xix, no. 2 



covering the work of these investigators is not deemed necessary in 

 this paper, however, since with the exception of that of Hoagland, none 

 of the foregoing researches are comparable with that herein reported, 

 for the reason that actual measurements of hydrogen-ion or hydroxyl-ion 

 concentrations were not made, total titratable acidity or basicity being 

 taken as a measure of the reaction. This leads to erroneous conclusions 

 where substances possessing a buffer nature, such as phosphates, are 

 present in solution. On the other hand, results obtained from the use 

 of solutions of single acids or bases are probably abnormal, since they 

 lack the antagonistic effects noted in more complete nutrient cultures 

 and probably operative under soil conditions. Furthermore, solutions 

 of single strong acids or bases of the concentrations ordinarily employed 

 in such work are extremely unstable and liable to large changes in reac- 

 tion. This is particularly true in alkaline solutions where absorption of 

 atmospheric carbon dioxid is not prevented. With organic acids there 

 is also the possibility of change in reaction due to bacterial infection 

 similar to that noted under series A of the present study. 



Hoagland {11) investigated the effect of reaction on the growth of 

 barley seedings grown in partial nutrient solutions of like osmotic con- 

 centration, in which the reaction was varied by the use of the various 

 potassium phosphates. Reaction was determined by use of the hydro- 

 gen electrode. He found a hydrogen-ion concentration of 0.7 X io~^ 

 (5.15 Pg) to be favorable to growth, while a concentration of 0.3 X io~^ 

 (3.50 Ph) was very toxic. A concentration of hydroxyl ions greater 

 than 1.8 X io~" (8.25 Ph) was found to be distinctly injurious, and when 

 exceeding 2.5 X io~^ (940 Pg) extremely toxic. It is unfortunate that 

 no solution of reaction between 3.50 Pg and 5.15 Pq was employed in 

 this work, since the former reaction was extremely toxic and the latter 

 favorable to growth. This is particularly true, since it has been shown 

 in the author's laboratory that this range of reaction represents a varia- 

 tion from a small to an unusually high total acidity (lime requirement) 

 in soils. 



In series B of the present study, a reaction of 5.94 Pg gave maximum 

 growth of wheat and soybeans, and in both cases a reaction of 5.i6Ph 

 was but slightly less favorable. With com seedlings maximum growth 

 occurred at a reaction of 5.16 Pg, while a reaction of 5.94 Pg was con- 

 siderably less favorable. Maximum growth of alfalfa occured in the 

 culture having a reaction of 5.94 Pg, M^hile a reaction of 5.16 Pg considera- 

 ably depressed the growth. A reaction of 4. 11 P^ was somewhat less 

 favorable to soybeans and distinctly less so to com, wheat, and alfalfa 

 than a reaction of 5.16 Pq. A reaction of 2.96 Pg resulted in the death of 

 all alfalfa plants in the culture, and while there was some growth of wheat, 

 soybeans, and com, at the time of harvesting the leaves of all plants 

 had begun to die at the tips. The roots of these plants produced no 

 lateral growth at this reaction and at time of harvesting had turned 



