PRINCIPLES OF ROTATION. ORDER. SAVING. 201 



much of it from a greater depth ; 3d, some plants, those, 

 namely, which have abundant foliage, draw much of their 

 food from the atmosphere ; others, like the grains, depend 

 more upon the materials contained in the soil. 4th, Par 

 ticular insects live upon certain kinds of plants, certain 

 flies, for example, on grains and grasses, and continue to 

 multiply as long as the same crop occupies the soil from 

 year to year. But when a crop intervenes 011 which these 

 insects cannot live, as beans or turnips, after wheat or 

 oats, then they perish for want of proper nourishment for 

 their young. 



712. The order in which crops succeed each other is 

 often of great importance. Weeds are a great injury 

 to all crops, and barnyard manure almost always carries 

 with it the seeds of many pernicious weeds. Such 

 manure should therefore be put into the ground when a 

 crop is to be cultivated, like corn or beets, which may be 

 kept free from weeds by the hoe and the plough or culti 

 vator. When the weeds have been destroyed or nearly 

 destroyed, by a hoed crop, a crop may follow of grain or 

 clover which cannot conveniently be weeded. 



713. Much may be saved by rotation. Each crop, in 

 succession, may find in the soil valuable matters which 

 were unnecessary to the preceding crops. Time may be 

 saved, which is more valuable than any crop, for lost time 

 is never found again. We must ascertain what is the 

 best succession of crops, and so arrange the different 

 crops in the different fields, as to occupy all the time of 

 the husbandman and yet not give him too much to do at 

 any one time. 



With sufficient forecast, this may always be done. 

 Suppose you can keep under cultivation twenty-eight 

 acres. You divide them into seven equal portions, and, 



