Oct. IS, 1919 Relation of Nutrient Medium to Plant Absorption loi 



neutral solution. This is also true of several other elements, particularly 

 NO3, although the concentration of NO3 was approximately the same in 

 the original acid and neutral solutions. The concentration of PO4 

 was, of course, greater in the original acid solution. 



THE EFFECT OF REACTION ON GROWTH AND ABSORPTION 



As was stated earlier in this article, all the nutrient solutions were 

 controlled with respect to hydrogen-ion concentration. This subject 

 has received some previous study in this laboratory. In an earlier inves- 

 tigation {16), it was shown that barley seedlings were not injured nor 

 inhibited by a hydrogen-ion concentration of Pg 5. More recent work 

 has confirmed these views for barley plants at all stages. Furthermore, 

 certain reports from the field regarding peat soils have indicated that 

 acidity of an intensity represented by Pg 4.8 or 5 is not injurious to a 

 large number of common agricultural plants. 



In some of these investigations the interesting fact was discovered 

 that in none of the nutrient solutions examined was there any tendency 

 for the plant to produce an excessive concentration of hydrogen or 

 hydroxyl ion, but that the opposite was true. Both alkaline and acid 

 solutions were brought approximately to the neutral point as a result of 

 absorption by the plant. In the water cultures of series 3, hydrogen-ion 

 concentrations were determined by colorimetric methods at each weekly 

 change of the nutrient solution, as follows : 



Table XIII. — Hydrogen-ion concentration of nutrient solutions afte 



plant for one week 



absorption by 



WATER CULTURES, SERIES 3 



At the end of the period of contact with the plant all solutions gave 

 an almost neutral reaction. Control experiments showed that no appre- 

 ciable change of reaction was due to the glass in contact with the solu- 

 tions. By referring to Tables IX and XII one may compare the changes 

 of hydrogen-ion concentration with the removal of the various ions 

 from solution. In general it may be said that absorption is so altered 

 in the acid solutions that larger percentages of a number of ions are 

 absorbed, as compared with the corresponding neutral solutions. NO3 

 and Ca are particularly affected. In the solution of 0.90 atmospheres 

 concentration and Pq 54 a considerably higher percentage of PO^ 



