14 ELEMENTS OF 



possess a declivity from the top to the bottom, to prevent 

 them from crumbling down and being undermined by 

 the current. 



When drains of this class are covered, they are gen- 

 ally made from two and a half to three feet deep, and 

 filled with stones or other loose materials to within a foot 

 of the surface. 



SUCCESSION OF CROPS. 



The experience of husbandmen from the earliest times 

 has shown, that the same kinds of plants cannot be ad- 

 vantageously cultivated in continued succession. The 

 same or similar species tend to grow feebly, or degener- 

 ate, or become more subject to diseases, when cultivated 

 successively upon the same ground. 



All herbaceous plants, w^hen cut in their green state, 

 ihat is, before they have matured their seeds, exhaust 

 the soil less than w^hen they remain until they have 

 ripened their seeds. 



GOOD RULES. 



\st, Crops consisting of plants of the same or similar 

 species, should not follow in succession, but should re- 

 turn at as distant intervals as the case may allow. 



2d, Crops consisting of plants whose mode of growth 

 or cultivation tends to the production of weeds, should 

 not follow in succession. 



3d, Crops whose culture admits of the destruction of 

 weeds, should be cultivated when we cultivate plants 

 which favor the production of weeds. 



And, Ath, when land is to be laid to grass, it should 

 be done when the soil is fertile and clean. 



When we find that land requires rest, we may lay it 

 down to grass for a longer or shorter time, taking care 

 when this is done, that the land shall be in as fertile a 

 state as circumstances will allow, and free of weeds. 



EXAMPLE. 



1st year, Turnips or other green crop, manured. 



