1-22 THE SOIL. 



wheat and half with rye, might therefore enable us to 

 estimate the extent of root sm^face in wheat and rye 

 plants. K the wheat crop from one-half of such a field, 

 reckoning by the hectare, receives as much phosphoric 

 acid and potash as the rye crop from the other half (17 

 kilogrammes of phosphoric acid and 39 kilogrammes of 

 potash), this would argue that the roots of the wheat 

 have come in contact with earth yielding as much nutri- 

 tive substance, and the earth with the same extent of 

 absorbent root surfaces, as in the case of the rye. If the 

 wheat crop contains phosphoric acid, potash, and silicic 

 acid, either more or less than the rye crop, this would 

 lead us to infer a larger or smaller ramification of the 

 roots. Experiments of this kind with rye, wheat, barley, 

 and oats are well worth making, although they have no 

 practical interest for the farmer, but merely a physiolo- 

 gical importance, and would finally lead to conclusions, 

 the correctness of which hes within rather wide hmits. 

 The absorptive power of the plant, and the time of ab- 

 sorption, make a difierence whicli, however, hereby 

 becomes perceptible. 



Of two plants, with the same absorbent root surface, 

 and pelding equal produce, one of which flowers and 

 ripens earlier than tlie other, the one with the shorter 

 period of vegetation must find somewhat more food, in 

 all the places which furnish its nutriment, in order to 

 receive the same amount as the other, which has a longer 

 time for absorption. 



Thus, the only hypothetical assumptions in determining 

 the above numbers are, that the food-absorbent root 

 sm-faces of rye and wheat are equal, and that the rye soil 

 yields neither more nor less than exactly 1 per cent, of 

 its nutritive substances. No doubt such a soil has no 

 actual existence ; but, supposing that we had such a soil 



