16 PLANT LIFE ON THE FARM. 



the fact that plants of such very different constitutions 

 grow on the same soil, but these facts are better explained 

 by the varying osmotic conditions of the plants. Cereal 

 crops and grasses generally are, for instance, specially 

 benefited by nitrogenous manures, though they contain 

 relatively little nitrogen as compared with clover and other 

 leguminous crops, but which, although they contain so large 

 a proportion of nitrogen in their constitution, are not par- 

 ticularly benefited by nitrogenous manures. Beetroots and 

 potatoes, which contain a considerable proportion of potash 

 in their constitution, are, nevertheless, not proportionately 

 benefited by the application of potash manures, though they 

 are so to some extent. These cases show that, by virtue 

 of the varying osmotic and digestive powers already men- 

 tioned, 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 re- 

 sults obtained by the chemist in the laboratory. If he fol- 

 lowed 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 conclude, 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, according to circumstances. 



