PHYSIOLOGY OF THE CORN PLANT '163 



sarily mean that the corn plant becomes less active in 

 absorbing nitrogen compounds as growth advances. The 

 explanation lies in the fact that the activity of the plant 

 in producing nitrogen-free substances increases rapidly 

 with growth. 



It is interesting to note that the young corn plant con- 

 tains no starch but a large percentage of nitrogen-fre6 

 extract, probably the most of which is sugar. Until the 

 plant reaches the stage at which the ear begins to form, 

 only a very small percentage of th'e sugar, is transformed 

 into starch. During the subsequent growth of the plant 

 the sugar is transferred in large quantities to the ear and 

 deposited as starch. At no time do the stalks and leaves 

 contain more than 6.55 per cent of starch, whereas, accord- 

 ing to the above table the dry weight of the ear is made up 

 of 62.77 per cent starch at the stage when the kernels are 

 hardening. A large percentage of the nitrogen taken up 

 by the corn plant during its early growth is later deposited 

 in the developing kernels. 



WATER REQUIREMENTS 



203. Leaf surface. — ■ On an acre of land producing 

 100 bushels of corn and three tons of stover there are ap- 

 proximately 11,000 pounds of dry matter. To produce 

 this large yield of dry matter it is necessary that an enor- 

 mous quantity of water pass through the plants. To 

 accommodate this rapid transpiration of water, the corn 

 plant is necessarily provided with a large leaf surface. 



204. Figuring tiie leaf surface of a com plant. — The 

 following method of figuring the leaf surface of a corn 

 plant is taken from "Corn" by Bowman and Crossley: 

 " In figuring the surface area of a leaf, measure the width 

 three inches from the ligule, also at a point six inches from 



