VEGETABLE FOOD. 277 



dent from experience, that it is only necessary and 

 useful for two purposes. The first is the destruction 

 of weeds, the second the amelioration of the soil. 

 After a course of four or five crops, which have been 

 only partially, or not at all weeded, root- weeds, par- 

 ticularly quitch, thistles, docks, and several others, 

 get possession of the soil, and render it impossible to 

 extirpate them without a summer fallow. On the 

 other hand, if land be of a strong, clayey, adhesive 

 nature, fallowing is absolutely necessary to prepare it 

 for the reception of seed. As to the idea that land 

 is benefited by exposure to the sun and air, except 

 for the purposes of desiccation and more perfect com- 

 minution, no greater error was ever conceived ; be- 

 cause it is well known, that the nutritive qualities of 

 the soil are fugitive under the action of the sun and 

 air. Laying light land into ridges, either by the 

 plough or spade, to receive a winter's frost, is, there- 

 fore, not only a waste of labour, but of some of the 

 best principles of the soil. 



Deep trenching, digging, or ploughing, is beneficial 

 to trees and all plants of robust character, not only 

 because it allows a greater range for the roots, but 

 also because it permits the ascent of warm and humid 

 vapours from the bowels of the earth. When the 

 staple of land is once well broken up for corn, deep 

 ploughing is not so necessary afterwards. 



The effects of different soils on the quality of 

 vegetable productions may just be noticed. Fruit 

 or vegetables raised on a light sandy loam, having a 



