GROWTH 01'^ TEA AND BARLEY CO^[PARRD. 155 



If we now inquire what demands are made upon tlie 

 soil by the two phmts, we find from Mayer's investiga- 

 tions (' Eesnlts of Agricultural and Chemical Experiments, 

 Munich, 1857,' p. 35), that the pea-seeds contain one-third 

 more ash constituents (3-5 per cent.) than the barley- 

 corns, and that the amount of phosphoric acid is pretty 

 much the same in both (2-7 per cent.). Therefore, all 

 other conchtions being equal, the subsoil from which the 

 pea derives its phosphoric acid must be as rich in that 

 ingredient as the arable surface soil which supplies it to 

 the barley. 



The case is different with nitrogen — for the same 

 amount of phosphoric acid, peas contain nearly twice as 

 much nitrogen as barley. Assuming both plants to derive 

 their nitrogen from the soil (which is, perhaps, not quite 

 correct in the case of peas), then for every milligramme 

 of nitrogen absorbed by the roots of the barley from the 

 arable surface soil, twice as much must be received by 

 the peas from the deeper layers. 



These considerations throw some light, I think, upon 

 the cultivation of peas ; for this plant requires a very 

 peculiar condition of the soil ; and it is more easy to con- 

 ceive that a ground exhausted by bearing peas slibidd 

 refuse to bear any more, than that the same soil, after tlie 

 lapse of some years, should again become fruitful for this 

 plant. 



According to tliese considerations, and assuming an 

 equahty of the absorbent root- surface in both plants, a 

 subsoil fruitful for peas must contain as much pliosplioric 

 acid, and tAvice as much nitrogen, as an arable surface soil 

 suited for the cultivation of barley. For the phosphoric 

 acid, the assumption is correct. 



We understand, without difficulty, the beneficial eni'ct 

 of manure upon an exliausted barley field. Barley derives 



