I02 Journal of Agrictiltural Research voi. xviii, No. 2 



was absorbed. In all cases the total quantity of PO4 absorbed was 

 greater with the acid solutions. The increased absorption from acid 

 solutions is also definitely indicated in figure 4. Here the total ionic 

 absorption as determined by conductivity measurements was consistently 

 greater in the solutions of Pg 5.1 as compared with solutions of Pg 6.8, 

 both of practically the same concentration. 



Even when solutions of single salts are used the absorption by the 

 plant does not bring about an unfavorable condition of acidity or alka- 

 linity. To determine the nature of such absorption, plants were grown 

 in favorable nutrient solutions until they had reached a stage of active 

 absorption. They were then transferred to solutions of sodium nitrate 

 (NaNOg), potassium chlorid (KCl), potassium sulphate (K2SO4), mag- 

 nesium sulphate (MgSO^) , potassium phosphate (K^P04) , and ammonium 

 chlorid (NH4CI). From the NaNOg solution a greater percentage of 

 NO3 than Na was absorbed, but equilibrium was restored by the forma- 

 tion of carbonic acid (HCO3) ion. This in equilibrium with carbon 

 dioxid (CO2) gave to the solution an approximately neutral reaction, 

 nor did other solutions tested acquire an excessive concentration of 

 hydrogen or hydroxyl-ion. K and CI were found to be absorbed in 

 equivalent quantities. The high alkalinity of the potassium phosphate 

 (K3PO4) solution was reduced to a condition of slight alkalinity. Further 

 details of these experiments are reported elsewhere (iS). 



In the complete nutrient solution it is impossible to say exactly what 

 ions and un dissociated salts are present before and after absorption 

 by the plant. Such a system, with its various hydrolyzable salts, is 

 very complex. Calculations of reacting values for the various elements 

 present indicate that an excess of acid radicles have been absorbed by 

 the plant, in greater degree from the solutions of acid reaction. 

 These have attained a practically neutral reaction after contact with the 

 plant, as noted above. Since the solution must remain balanced with 

 respect to positive and negative ions, some other ions must have been 

 formed in the solution. Where NO3 is absorbed in large percentage it is 

 probable that CO3 or HCO3 become important constitutents of the solu- 

 tions. A small quantity of silicate radicles is also found, derived from 

 action on the glass. The resultant reaction is due to the particular state 

 of equilibrium existing among all these constituents ; and while we may 

 determine the hydrogen-ion concentration with considerable accuracy, 

 the data at present available do not enable us to determine the exact 

 relations between the different components of the system. 



THE EFFECT OF THE NUTRIENT SOLUTION ON THE CELL SAP 



That the concentration of the nutrient medium is reflected to a certain 

 extent in the cell sap has been shown by McCool and Millar (30). In 

 another article by the present author ^ are described determinations 



1 In course of publication in Bot. Gaz. 



