Apr. 15, 1920 Effect of Solution Reaction on Germination and Growth 87 



result of the variation in reaction, yet it should be noted that certain 

 other factors might have been operative to an undetermined extent. 



Attention has already been called to the probable small variations in 

 osmotic concentrations of the cultures within a given series. It seems 

 doubtful whether such variations could have exerted any appreciable 

 effect. 



There was a variation in sodium content from an equivalent concen- 

 tration of zero in culture i to 0.0360 in culture 7 of series B. It has 

 recently been shown in the researches of Shive (25) that the substitution 

 of an equivalent amount of sodium phosphate (NaH2P04) for part of the 

 potassium phosphate (KH2PO4) of a 3-sait nutrient culture produced 

 considerable increases in the growth of soybean seedlings. In the 

 present work, however, the greatest variations in growth were associated 

 with the smallest changes in sodium content. Thus culture 2, to which 

 had been added sodium as NaOH equivalent to 0.0144 ^^- was appar- 

 ently below the critical reaction for all plants studied, while maximum 

 growth of all plants was obtained in either culture No. 4 or No. 5 to which 

 had been added NaOH equivalent to 0.0181 m. and 0.0198 m., respec- 

 tively. It seems highly improbable that the variations in grov/th could 

 have been to any appreciable extent induced by such small variations in 

 the total sodium content. 



The contents of calcium and magnesium employed in the cultural 

 solutions were purposely kept low. (See Table I.) There was never- 

 theless a trace of precipitate of the phosphates of these metals formed in 

 culture 6, which had a reaction of 6.97 Ph, and a somewhat more abun- 

 dant precipitate in culture 7, which had a reaction of 7.71 Ph- To what 

 extent the change in concentration thus produced might have influenced 

 the results was not determined. Attention has previously been called 

 to the possibility of similar changes in solubility of these elements at 

 corresponding reactions under soil conditions. 



In the work of Shive {25), previously mentioned, a toxicity of mono- 

 basic phosphates was shown toward soj^beans grown in soil and in solu- 

 tion culture. While a general relation between the degree of injury 

 sustained by the plants and the total acidity of the cultures was noted in 

 this work, the fact that determinations of hydrogen-ion concentration 

 were not made prevented accurate conclusions as to the actual part 

 played by the acidity factor in the production of the injurious efifects 

 associated with the monophosphate group. The data obtained in the 

 present study indicate that there was probably little effect of the HjPO^ 

 group aside from that produced by the hydrogen ion formed in its dis- 

 sociation. This is brought out by the fact that in culture 4 there was 

 maximum growth of corn seedlings and very nearly maximum growth of 

 wheat and soybean seedlings; whereas in the composition of this solu- 

 tion, H3PO4 equivalent to a concentration of o.orSo m. and NaOH 

 equivalent to a concentration of 0.0181 m. were employed — that is, 



