FACTORS OF AGRICULTURAL PRODUCTION 161 



The following table shows, approximately, the food-producing 

 powers of an acre of land under different crops : 



Two things must be said, however, in qualification and explana- 

 tion of this table. In the first place, food values are not to be 

 measured in calories alone. Digestibility and appetizing qualities 

 are of great value, to say nothing of the bone- and muscle-building 

 power of certain ingredients. Therefore it does not follow that 

 a sweet-potato diet is to be commended merely because an acre 

 of this crop yields a large number of calories, though it does 

 show that, when the product is so appetizing and digestible 

 as the sweet potato, a considerable economy of land could be 

 effected by a larger consumption of that vegetable. 



] n the second place, the yields per acre are only estimated on 

 the basis of general observation. These estimates are not based 

 upon statistics of average yields, nor upon maximum yields actu- 

 ally secured. They are merely what, in the author's opinion, an 

 average acre of land, properly situated for the crop in question, 



1 The figures in this column are taken from Bulletin 28, of the United States 

 Department of Agriculture, Office of Experiment Stations, by W. O. Atwater, 

 Ph. I)., and Charles D. Woods, B. S. (Government Printing Office, 1896). 



