SOIL EXHAUSTION AND ROTATION OF CROPS. 193 



any impulse which it receives from the plant (that is, the root 

 must not necessarily weigh so much or measure so much), but 

 depends also upon the nature of the soil. Where this is rich tho 

 roots tend to remain ; they branch and ramify through all the 

 pores of a small bulk of earth. Where this is poor they stretch 

 off and are sparsely distributed through a larger space. Where 

 they find plenty of food they grow and multiply upon it; where 

 nourishment is lacking they seem to go in search of it. All ob- 

 servations must therefore be comparative. • We know, however, 

 in a general way, that the development of roots is different in 

 different classes of plants. We know that clover has a much 

 deeper system of roots than our ordinary grains. We know that 

 where the soil is rich at the surface, and where it is adapted nat- 

 urally, by its mechanical condition to the growth of wheat, for 

 example, the large proportion of wheat roots are found within a 

 rather narrow space. On the fertife plains surrounding the town 

 of Leipzig, the principal commercial city of Saxony, situated in 

 one of the richest agricultural regions of Germany, I have seen 

 the same kind of plow going back and forth, which you will find 

 pictured in the classical dictionaries as used by the Romans. If 

 you should take a shingle five inches wide and sharpen it to a 

 blunt point, you would have about the shape of the plowshare I 

 refer to. 



This wooden instrument, shod with thin iron, did not turn a 

 furrow; it simply made a groove about four inches deep from 

 crest to base, stirring and mixing the soil thoroughly, however, 

 to that extent. This was the only kind of plowing I saw practised 

 on these fields in 1854, and yet splendid crops were harvested 

 from them. The soil was doubtless naturally of excellent texture 

 and allowed a due penetration of the roots. But the fact remains 

 that with such tillage all fertilizing applications must remain near 

 the surface, and this makes evident that the roots of our grains 

 need not go down to any very great depth. If the soil has 

 nourishment and moisture for them, six or eight inches of earth 

 will answer for the support of a crop. A foot will, in a majority 

 of cases where the soil is of good quality, contain the bulk of the 

 roots of the wheat crop. They may go deeper, as Schubart ob- 

 served, but only because they must descend in order to find food 

 or drink. It has been shown by experiment that roots develop in 

 poor soil in 'the vicinity of any enriching material ; so that we 

 cannot say, because Indian-corn roots have been traced for twenty 

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