50 AGRICULTURE. 



3d. Vegetables, whether of the same family or not, 

 having a similar structure of roots, should not succeed 

 each, other. It has been observed that trees suffer 

 considerably by the neighbourhood of sainfoin and 

 lucerne, on account of the great depth to which the 

 roots of these plants penetrate ; whereas culmifer- 

 ous grasses do them no harm. 



4th. Annual or biennial trefoils prevent the escape 

 of moisture from sandy and arid soils, and should 

 constantly cover them in the absence of other 

 plants ;* while drying and dividing crops, as beans, 

 cabbages, chicory, &c., &c., are lest jilted to correct 

 the faults of stiff and wet clays. 



5th. When plants are cultivated in rows or hills, and 

 the ground between them is thoroughly worked, the 

 earth is kept open, divided, and permeable to air, heat, 

 and water, and, accordingly, receives from the atmo- 

 sphere nearly as much alimentary provision as it gives 

 to the plant. This principle is the basis of drill hus- 

 bandry. 



6th. All plants permitted to go through the phases 

 of vegetation (and, of course, to give their seeds), ex- 

 haust the ground in a greater or less degree ; but, if 

 cut green and before seeding, they take little from the 

 principle of fertility. 



7th. Plants are exhausters in proportion to the length 

 of the time they occupy the soil. Those of the cul- 

 miferous kinds (wheat, rye, &c.) do not ripen, if 

 sown in the fall, under ten months, and during this 

 period forbid the earth from being stirred; while, 

 on the other hand, leguminous plants occupy it but 

 from three to four months, and permit frequent 

 ploughings. This is one reason why culmiferous 



biennio seritur farreo spico, id est aristato, quod, ne fiat solent, 

 qui pradia locant, excipere." 



* The "sterilis tellos medio versatur in aestu" the bare 

 earth turned up in midsummer of Virgil, shows the opinion 

 he entertained of a husbandry that left the fields without vege- 

 tation. 



