42 PLANT SUCCESSION AND CROP PRODUCTION 



duction of spring wheat. It is the invention of a milling device 

 which made possible the manufacture of a handsome white flour 

 from spring wheat. This device called the purifier, separated the 

 bran and endosperm better than any previously known machine 

 had done. But this machine, invented a generation ago, did not 

 establish the spring wheat center. It only intensified the already 

 increasing production. This helps one to understand how the eco- 

 nomic factors operate in crop distribution. They do not create 

 the conditions for plant growth, but profit is largely the determinant 

 which carries on or halts crop production. 



In the ecological study of the vegetation, climatic conditions 

 are put down as the broad general determiners. The edaphic fac- 

 tors modify the effect of climate. In favorable soils, the center is 

 extended. In unfavorable soils, even well within the center, the oc- 

 currence of certain plants is prevented. 



In the crops the economic factors increase or diminish pro- 

 duction. The physical factors determine whether or not a certain 

 plant may grow, but the profit determines whether or not produc- 

 tion will increase. This is the problem of the food administrator ; 

 to make the price of wheat, say, high enough to tempt the farmer 

 to increase production, and at the same time not to put it out of 

 reach of the majority of consumers. The relation of the economic 

 factor to crop production is analogous to the relation of the edaphic 

 factors to the climatic in the natural vegetation. The edaphic 

 factors have such an influence in modifying the climatic that the 

 occurrence of a certain plant is the direct result of the edaphic in- 

 fluence. The economic factors have such an influence in modifying 

 crop production, that even though the underlying climatic and soil 

 factors are suitable, production is still limited by the profits. 



