PHYSIOLOGY OF THE CORN PLANT 165 



ply of plant-food in the soil will increase the water require- 

 ments of the crop growing on that soil. 



The investigations have shown the water requirements 

 of corn to be greatly affected by atmospheric conditions. 

 Other things being equal, the rate of transpiration is faster 

 and the water requirements are greater in an arid than in 

 a- humid atmosphere. Shading to the extent of reducing 

 photosynthesis, tends to increase the water requirement. 



Montgomery compared narrow-leaf and broad-leaf 

 types of corn with the result that the broad-leaf types 

 showed the higher water requirements. ' 



206. Amount of water required. — A summary of the 

 water requirement measurements of corn by different 

 investigators shows considerable variation as would be 

 expected owing to the fact that these investigators worked 

 under quite different conditions, and with different vari- 

 eties. To produce one pound of dry matter in corn required 

 the absorption and transpiration of the following nmnber 

 of pounds of water as given by the different investigators: 

 King working in Wisconsin, 350; Widtsoe working in 

 Utah, 386; Briggs and Shantz, working in Colorado, 369; 

 Wollny working in Germany, 233; and Leather working 

 in India, 337. 



GROWTH 



207. Growth. — Those changes involved in the growth 

 of a corn plant may be grouped into two clases. The first 

 group of changes have to do with the "extension" of the 

 plant or its increase in lengthi and size. The second group 

 of changes result in a change of the internal structure 

 of the plant or differentiation of the cells into special 

 organs with more or less definite functions. 



The increase in length and size of the plant results from 



