Oct. IS, 19 19 Relation of Nutrient Medium to Plant Absorption 



93 



on the basis of the original solution. At the end of the experiment 

 composite samples were made of each solution, and these were analyzed 

 for the important elements present. The results are shown in Table VII. 



Tabls VII. — Analyses of nutrient solutions of different concentrations after growth 



of plant 



WATER CULTURES, SERIES 2 



o Solutions not changed for 16 weeks. 



Absorption continued until a large percentage of the total ions present 

 were absorbed. In two cases the NO3 ion was completely removed. 

 The Ca, Mg, and SO4 were absorbed in lesser percentage than the NO3, 

 PO4, and K. The percentages of absorption for the given ions were not 

 dissimilar in the three concentrations; therefore, under these conditions, 

 the total absorption was approximately proportional to the concentra- 

 tion of ions present in the original solution. In the supplementary 

 cultures in which the solutions were not changed between the ages of 

 6 weeks and maturity, practically all of the NO3, POj, and K have been 

 removed from the solution. It is interesting to note, however, that 

 100 per cent removal is effected only in the NO3 ion. This fact may 

 perhaps be explained by the nature of the metabolic processes in the 

 plant. The NO3 ion undergoes complete chemical transformation, and 

 at certain stages may disappear entirely from the sap, while the other ions 

 are always present. Thus the equilibrium conditions would differ in the 

 two cases. 



In the third series of water cultures the procedure was varied by chang- 

 ing the nutrient solution regularly each week throughout the whole 

 growth of the plant, for 15 weeks. At each change of solution conduc- 

 tivity measurements were made, and the average absorption of electrolytes 

 for the week was computed. The plants were grown two in each jar of 

 approximately i,ooo-cc. capacity. After 10 weeks part of the jars were 

 changed to a concentration of o.io atmospheres, while the other were 

 continued with concentrations of 0.90 atmospheres. In each case both 

 neutral (Pg 6.5 to 6.8) and acid (Pq 5.1 to 5.5) solutions were compared 

 under otherwise similar conditions. The composition of the solutions 

 is given in Table VIII. 



