gl2 THE POTATO 



almost indefinitely. The one exception to this is 

 lime, and its use is generally considered to be more 

 to make conditions right for the making available 

 of other elements than as an element of plant food 

 itself. 



The potato plant — leaf, vine, stem, root, and 

 tuber — is composed of elements taken from the soil 

 and air. The plant is started from stored-up nutri- 

 ment in the tuber or part thereof that is planted. 

 After the start, the rootlets take water (hydrogen 

 and oxygen), nitrogen, the phosphates, potash and 

 the other mineral elements from the soil. These 

 are taken up by the movement of sap to the leaves. 

 The leaves take carbon and oxygen from the air 

 through the stomata or breathing pores on their 

 under surface; the various elements are trans- 

 formed by the sunshine, heat, protoplasm and 

 chlorophyl, and water (hydrogen and oxygen) and 

 carbonic acid gas are given ofif by the leaves. The 

 food which is manufactured or transformed is 

 deposited throughout the plant. A large part of it 

 goes to the storehouse of the enlarged underground 

 stem or tuber. 



An average plant is made up somewhat as fol- 

 lows: 



Phosphate, potash and other minerals (from 



the soil) 5.0 per cent. 



Nitrogen (from the soil and air) . . . 1.5 per cent. 



Hydrogen (from water) 6.5 per cent. 



Oxygen (from water and air) . . . . 42 . per cent. 



Carbon (from air) 45 . per cent. 



From this it appears that Nature is lavish in its 

 suppUes, and that the soil, the condition of which is 

 more or less under the control of man, contributes 

 a comparatively small share in the plant's economy. 



