ON THE FOOD OF PLANTS. 131 



any comparatively extraordinary luxuriance of 

 vegetation. And, as a practical demonstration 

 that dung, when laid on or near the surface, and 

 repeatedly turned over and exposed to the ac- 

 tion of the atmosphere, is not very rapidly or 

 very effectually exhausted, I shall state a course 

 of operations which were carried on in a field of 

 about six acres, within my immediate observation. 

 The soil of this field was a fine friable loam, 

 and of a black colour, but the surrounding 

 land, although of the same texture, was of a 

 foxy brown ; this difference in the colour, no 

 doubt, was occasioned by the difference in cul- 

 tivation and manuring. The surrounding lands 

 had been treated in a careless, slovenly manner, 

 as a common farm ; whilst the field in question 

 was cultivated as a market-garden, cropped with 

 esculent vegetables, and manured at least once 

 in the year, for many years. At the period it 

 came under my notice the market-gardener had 

 died, and it fell into the hands of another per- 

 son, who having but seven years to run of a 

 lease, determined, as he said, to work it out ; 

 he therefore sowed it with white wheat for five 

 years following, without giving any manure. 

 The first year, it produced forty-eight bushels 

 per acre, and every year after, the crops declin- 

 ed three or four bushels per acre. The sixth 



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