CARBONIC ACID A FOOD FOR PLANTS. 83 



gum and gelatine have been thus fed to plants, with the ef- 

 fect of making them grow vigorously. A great variety of 

 organic substances containing carbon may therefore be ab- 

 sorbed into the plants and afford nourishment. Practical 

 farmers act on this principle and it forms the basis of many 

 of his operations and daily labors as he accumulates a stock 

 of organic substances in the form of manures as food for his 

 crops. 



