34 



Science of Plant Life 



bered that the plants that produce this food take a consider- 

 able part for their own maintenance, and that the part which 

 the farmer harvests is the plants' surplus. The table given 

 below shows the average yield per acre; its food value cal- 

 culated in Calories ; ^ and the number of men that i acre 

 planted to different crops might feed for i day, assuming that 

 each man requires 3000 Calories per day. 



If the plant products of an average acre are fed to cattle, 

 the dressed beef produced amounts to only 125 pounds, 

 yielding an energy equivalent to the food of 43 men for i day. 

 If transformed into pork, the yield is 273 pounds, or sufficient 

 food for 220 men for i day.^ This shows the great loss of 

 energy that results when plant foods are converted into meat 

 before they reach the human consumer. It is evident that as 

 the human family becomes larger and food becomes scarcer, 

 we shall have to take more and more of our foods directly 

 from plants. 



' A Calorie is the amount of heat necessary to raise the temperature of i kilo 

 of water i degree Centigrade. 



' United States Department of Agriculture, Farmers' Bulletin No. 877. 



