AGRICULTURAL ECONOMICS 



wants of his household; but Thaer lived at a 

 time when commerce had so developed and indus- 

 try had become so diversified that production for 

 the market had become very important. The fol- 

 lowers of Thaer learned to select those crops 

 which would enable them to win the largest net 

 profits, and to exclude all others from the field- 

 system. 



This process of selecting the crops which en- 

 able the farmer to win the largest net profits is 

 an important factor in determining the geograph- 

 ical distribution of farm crops in modern times. 

 While all plants will not thrive under the same 

 conditions, there are usually several species pres- 

 ent to compete for the use of each piece of land. 

 When Nature is left to herself, the plants which 

 are best fitted for this competitive struggle sur- 

 vive and occupy the land; but when man inter- 

 venes the useful plants are given especial care 

 while the plants which are harmful or of no use 

 are destroyed. 



Under the self-sufficing economy of earlier 

 times, all the useful plants which could be made 

 to thrive were cultivated on each farm. The 

 greater the variety of crops which each husband- 

 man could produce the greater the degree of his 

 well-being, for each household was a little eco- 

 nomic world striving to subsist upon the imme- 

 diate products of its own industry. 

 ' But under the regime of modern commercial agri- 



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