38 PLANT SUCCESSION AND CROP PRODUCTION 



Pennsylvania only the best fields are ever used for growing com. 

 These are reinforced and amended by a liberal use of manures. 

 This coddling is carried out to a greater degree in the Connecticut 

 River Valley where tobacco is grown. Not only are the soils treated, 

 but the plants are sheltered under cloth. This cuts down the tran- 

 spiration rate during the day and at night prevents loss of heat. 

 The climate thus produced is more like that of the center of the 

 tobacco industry. 



With the crop plants then, climatic optimum is not the factor 

 which determines the center. The soil conditions are not always the 

 controlling factor. It is the profits. 



It is profit which causes the potato crop to center, (Fig. 4) 

 near each of the thirty largest cities of the United States without 

 much indication of climatic or soil preferences. It is profit which 

 links the corn belt with the center of oats production, though the 

 former is pushed upward from the south and the latter down from 

 Canada. Profits makes New York and New England a large 

 meadow of imported cultivated grasses, while the native prairies 

 and plains grasses only come to market if pastured. 



An economist attempting to minimize what he regards as an 

 undue preponderance of the physical factors would explain these 

 distributions on the theory of rent. He would imagine a hypotheti- 

 cal state. This state would be circular in outline and present no 

 differences in climate, topography or soils. All transportation prob- 

 lems that existed would be equally distributed over the state. Under 

 such conditions, the state would be divided into many concentric 

 zones. Around the city would be truck gardens ; next to these, a 

 dairying community; next, grain farms; and in the outmost circle 

 pasturing would be the chief agricultural endeavor. (Fig. 5). The 

 explanation of the zonation of this unusual state would be that the 

 grain farmer, making more profit than the shepherd, could afford 

 to pay more rent than the latter and so live closer to the city and 

 his market. The dairyman's rent would be higher than the grain 

 farmer's, and so on into the city- The economist has a good case 

 and there is no way of circumventing his argument. We see ex- 

 amples of the working out of this hypothesis on every side. 



Now the truth of the matter of crop production and the cen- 

 tering of crops in certain localities lies somewhere between the 

 geographic considerations of climate and soils and the purely hypo- 

 thetical proposition of the economists. They cannot escape, under 



