PLANT NUTRITIOK. 21 



nevertheless, not proportionately benefited by the appli- 

 cation of potash manures, though they are so to some 

 extent. These cases show that, by virtue of the varying 

 osmotic and digestive powers already mentioned, the 

 plants in question take what they want, and when they 

 want it, and are not induced to take more by the addi- 

 tion of larger supplies. They further show the errors 

 that may arise from the farmer acting too implicitly on 

 the results obtained by the chemist in the laboratory. If 

 he followed the indications of the chemist unchecked by 

 other experience, he would apply to his land what was 

 really not required by the crop. Thus Messrs. Lawes and 

 Gilbert tell us that the exact composition of the crops is 

 no direct guide to the description and amount of manurial 

 constituents that will be most effective, thus although 

 wheat removes more phosphoric acid from the soil than 

 does barley, yet the application of the phosphate is more 

 beneficial to the barley than to the wheat. They con- 

 clude, then, that it is not necessary to supply to the land 

 all the constituents that have been removed from it, or 

 that would be contained in the crops it is wished to grow, 

 but that we should supply all or some, more or less, ac- 

 cording to circumstances. 



