96 Journal of Agricultural Research voi. xvm, no. 2 



changed every two days in the lower concentrations and every three 

 days in the others. Ten bottles with 20 plants were used for each solu- 

 tion. Four concentrations were tested 0.07, 0.58, 0.90, and 1.70 atmos- 

 pheres. In each concentration, solutions of both acid and neutral reac- 

 tion were subjected to experiment. The composition of the solutions 

 was such that in each concentration the acid and neutral solutions had 

 practically identical freezing-point depressions and as nearly as possible 

 the same ionic ratios. The exact composition of the solutions is given 

 in Table VIII. The plants were grown out of doors in a uniform light 

 from June 26 to August 22. The bottles were so arranged and changed 

 in position that the light and temperature conditions were essentially 

 the same for all cultures. 



When the plants had grown for 6 weeks, the absorption study was 

 made for a period of 72 hours. The original solutions were analyzed for 

 Ca, Mg, PO4, NO3, K, and SO4; and the same solutions after contact 

 with the plant and after they had been made up to original volume were 

 again analyzed. The differences between the two analyses represent the 

 change in concentration due to 72 hours' absorption by the plant, ex- 

 pressed as parts per million of the various ions. The total quantities re- 

 moved are obtained by multiplying the parts per million change by the 

 volume of the solution. 



The data incorporated in the above table furnish a basis for a number 

 of interesting suggestions concerning absorption. In the first place it is 

 noted that in the lowest concentration the percentage of absorption for all 

 elements is much greater than in the two highest concentrations. This is 

 in accord with the results from the first series of water cultures. The 

 total quantities absorbed per plant are much greater in the concentration 

 of 0.90 atmosphere as compared with 0.07 atmosphere, but in the highest 

 concentration there is no corresponding increase and in a number of 

 instances there is a decrease. If a large number of solutions were em- 

 ployed with small increments in concentration, we may infer that the 

 total quantities absorbed would increase up to a certain total concentra- 

 tion and then would remain constant or decrease. Since the percentage 

 of absorption, however, might be different there would not be necessarily 

 a direct proportionality between the concentration of each ion and the 

 quantity absorbed. Some data are cited by Pouget and Chouchak (34) 

 in support of the assertion that NO3 absorbed by wheat seedlings is pro- 

 portional to the concentration up to a certain point. This could not be 

 finally decided except under conditions which pennitted absorption 

 studies with controlled conditions of concentration over various time 

 periods. 



