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most valuable generalizations of science is the demonstrated 

 truth that certain known constituents of the soil do in the 

 process of vegetable growth, enter into the essential constitu- 

 tion of the plant, and as a consequence that these constituents 

 are removed from the soil in the removal of the plant of which 

 they form a part. These indispensable substances of the soil 

 compose but a veiy small portion of its bulk, and they are not 

 replaced by any process of nature, certainly not by any process 

 rapid enough to keep pace with the succession of crops. To 

 restore the conditions of vegetation, they must be replaced by 

 man. Every crop diminishes the capacity of the land for the 

 production of another crop. This diminution may not be per- 

 ceptible in its immediate influence upon a virgin soil, rich in 

 the necessary elements of vegetation. Years, even generations, 

 may elapse before these mineral deposits shall seem to fail. 

 Rotation in the crops will equalize the drain upon the difler- 

 ent portions of the soil. The yearly agitations of the plough 

 will bring to the roots of the plant other particles of earth 

 whose virtues have not been extracted, and the steady action 

 of the sun upon the changing surfaces exposed to its rays, will 

 develop new resources of vegetative power. These and other 

 causes will postpone the day of exhaustion. That day when 

 it comes, is one of wrath, of ruin and desolation for the work 

 of civilized man. The imposing fabric moulders, crumbles 

 and falls. The fertile plain once Avaving with bountiful har- 

 vests and sustaining populous and well built cities, becomes a 

 barren waste. The blasted fields of ancient agriculture are 

 to-day monuments of the vengeance which nature wreaks upon 

 a culture that does not compensate the soil. The Roman 

 Campagna was once the garden of Italy from which the mil- 

 lions of the imperial metropolis drew daily supplies of food. 

 Here was the site of the luxurious country-seat, the splendid 

 villa, the estate of the Roman senator. Here were purple 

 vineyards, and rolling landscapes covered with golden grain. 

 Here, too, were temples of the gods. Now a noisome desert 

 exhales a poisonous miasma and affords the prowling robber a 



