PLANTS IN THEIR RELATION TO HUMAN WELFARE 133 



gines was supplied from the forests. About one hundred and 

 fifty years ago, coal was discovered in Pennsylvania, and one 

 would suppose that since that time our forests would have 

 been drawn upon less heavily for fuel. But it is estimated 

 that the United States burns annually at the present time 

 one hundred million cords of wood. While we are consider- 

 ing the uses of plants as fuel, we should remember that our 



FIG. 65. A view showing how the forests of the Coal Period probably 

 looked. (Tarr and McMurry.) 



enormous coal beds were without doubt formed from great 

 tree ferns and other plants which lived in bygone ages. Pe- 

 troleum, too, from which our kerosene oil is produced, is 

 believed to be a product of plant decomposition. 



One has but to call to mind the enormous use of trees for 

 framing and finishing houses, for furniture, for railroad ties, 

 telephone and telegraph poles, for shipbuilding, and for 

 boxes, barrels, and paper manufacture, to realize how seem- 



