302 



BOTANICAL GAZETTE 



[OCTOBER 



similar in the soil solution and soil extract. As previously shown, 

 the extract may contain several times the quantity of solutes 

 actually found in the soil solution; that is, in the free water of the 

 soil when it contains optimum percentage of water. The magni- 

 tudes have been calculated by the methods of Bouyoucos and 

 McCooL. Estimates of the concentration of ions present in the 

 soil solution indicate that invariably the plant sap has a much 

 greater concentration, and in the case of K and PO4 ions many 

 times greater. It is evident that the relation of the ions to each 

 other is also quite different in the two cases. In the soil solution 



TABLE II 

 Analyses of plant sap and soil extracts 



* From 30-50 per cent in form of NO3 nitrogen. 



t Extracts are much more dilute than soil solution, the total concentration of which is shown by 

 table I. 



Ca is present in about the same magnitude as K; in the plant 

 sap the concentration of K is from 5 to 10 times that of Ca. The 

 ratio of Ca to Mg is not very dissimilar, Ca exceeding Mg in all 

 samples, both in the plant and soil. 



The question has often been discussed whether the plant 

 reflects the composition of the soil. It is the general consensus 

 of opinion that the analysis of the plant ordinarily gives no indica- 

 tion of the deficiencies or fertilizer needs of a soil. This could 

 scarcely be expected, of course, in view of the complex and chan- 

 ging nature of the two systems of the plant and soil. Moreover, 

 analyses of the mature and ripened plant, such as usually have 

 been made, could not possibly give any insight into the relation 

 of the plant to the soil in the period of active growth. It cannot 

 be too strongly emphasized that both the plant and soil are 



