Oct. IS. 1919 Relation of Nutrient Medium to Plmit Absorption 83 



pheres. It is not certain, however, that the o.io atmospheres concen- 

 tration was always constant, in spite of the great volume of solution used. 



Especially interesting are the data showing in percentages the com- 

 position of the different parts of the plant. Some idea may be gained 

 here of the influence of concentration on the absorption of individual 

 elements and of the distribution between roots and tops. In the first 

 place, the analyses of the tops show an increase of N from 2.65 per cent 

 in the concentration of o.io atmospheres to a maximum of 4.03 per cent 

 in the concentration of 0.78 atmospheres. lyikewise the total K increases 

 nearly 100 per cent. No such increase is noted, however, for PO4, Ca, 

 or Mg. The NO3 also increases regularly with increasing concentration, 

 and in the higher concentration about 0.5 per cent of nitrate nitrogen is 

 found. 



The elements soluble in cold water were determined by shaking the 

 dried and ground sample with an excess of water, filtering, and then 

 estimating the total quantity of each element found, the final calculation 

 being based on the weight of dry material. The striking increase in 

 percentage and total quantity of K in the tops of eadi plant is largely 

 referable to K soluble in water. Most of the P and almost all of the Mg 

 were soluble. Only about two-thirds of the Ca was soluble. 



When we examine the data from analyses of the roots we meet with a 

 different set of relations. There is an increasing percentage and total 

 quantity of N and K, as in the tops; but, unlike the tops, the roots 

 show very large increases in PO4, Ca, and Mg. The partition between 

 soluble and insoluble fractions shows that the increase is principally due 

 to insoluble forms of the elements. The data suggest the hypothesis 

 that with increasing concentration insoluble phosphates of Ca and Mg 

 are precipitated in the roots, while the tops of the plants principally store 

 excess N and K. 



It should be repeated that in this experiment the large containers 

 (5-gallon jars), together with frequent changes of solution, maintained, 

 with the possible exception of the lowest concentration, an approximately 

 constant concentration at the different levels. Thus the results indicate, 

 at least in a general way, the influence of concentration rather than the 

 limitation of insufficient total quantities. When such concentrations are 

 maintained continuously, it is apparent that the plant may attain a con- 

 dition in which the percentage of certain elements in its composition is 

 very high, far higher than for plants grown under different conditions 

 or in the field. It is of course understood in a general way that fertiliza- 

 tion may affect the composition of the crop, but only in an experiment 

 of the kind outlined above is it possible to point out definite and logical 

 relationships. Also, it is practically impossible to obtain reliable results 

 from the roots of plants except in sand and water cultures. It is not 

 practicable to recover the roots from the soil quantitatively, and con- 

 tamination is unavoidable. The results from this experiment are 

 122504°— 19 3 



