164 FIELD CROPS FOR THE COTTON-BELT 



the. tip of the leaf. Add these two widths, divide by two 

 to get the average. Multiply this average width by the 

 length of the leaf from the ligule to that point, six inches 

 from the tip. To the area of this rectangle add the area 

 of the isosceles triangle at the tip of the leaf, which is six 

 inches in altitude, and as wide as the leaf is at that point. 

 The sum of the two areas gives the leaf surface on one 

 side of a single leaf. Multiply this sum by two and the 

 entire surface of leaf will be ascertained. For approxi- 

 mate calculations, the surface of one leaf multiplied by 

 the niunber of leaves on the stem will give the entire leaf 

 surface of the stalk." ^ 



205. Conditions affecting water requirements. — The 

 term "water requirement" as here used indicates the ratio 

 of the weight of water transpired by a plant during its 

 growth to the dry matter produced. Studies of the water 

 requirements of corn by King, Widtsoe, Montgomery, 

 Briggs and Shantz of this country, Wollny of Germany 

 and Leather of India have dfemonstrated quite clearly 

 that environmental factors are important in determining 

 the efficiency with which the corn plant uses its water. 

 The investigations indicate that when growing in a soil 

 containing the optimum moisture content, corn will pro- 

 duce more dry matter to the unit of water transpired than 

 when growing in a very wet or a very dry soil. 



There is in most cases a reduction in the water require- 

 ments of corn when fertilizers are used, especially if the 

 soil in question is a poor one. It has been pointed out 

 that a high water requirement is often due to a deficiency 

 in the soil of a single plant-food element in which case 

 growth practically ceases while transpiration goes on. 

 It is probably true that any condition that limits the sup- 

 ^ Bowman and Crossley, " Corn," p. 52. 



