126 THE SOIL. 



more earthy particles yielding nutriment, i. e. the rye 

 soil would necessarily produce an average wheat crop, 

 which however is not the case. 



The comparative returns, in corn and straw, from a 

 rye soil, which has been sown simultaneously half with 

 wheat and half with rye, might therefore enable us to 

 estimate the extent of root surface in wheat and rye 

 plants. If the wheat crop from one-half of such a 

 field, reckoning by the hectare, receives as much phos- 

 phoric acid and potash as the rye crop from the other 

 half (17 kilogrammes of phosphoric acid and 39 kilo- 

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

 the wheat have come in contact with earth yielding as 

 much nutritive 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, pot- 

 ash, 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 mak- 

 ing, although they have no practical interest for the 

 farmer, but merely a physiological importance, and 

 would finally lead to conclusions, the correctness of 

 which lies within rather wide limits. The absorptive 

 power of the plant, and the time of absorption, make a 

 difference which, however, hereby becomes perceptible. 



Of two plants, with the same absorbent root surface, 

 and yielding equal produce, one of which flowers and 

 ripens earlier than the 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 deter- 

 mining the above numbers are, that the food-absorbent 

 root surfaces 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 before us, and were to put the question how 



