18 THE BOOK OF WHEAT* 



Generally cells reach their full size in a brief time, and con- 

 tinuous growth depends mainly upon the constant and rapid 

 formation of new cells. The essentials to growth are light, 

 air, moisture, heat and food. In the absence of any one of 

 these, the plant dies, and in their disproportionate combina- 

 tion, growth is sickly. In germination, food is furnished by 

 the seed, and light is not essential. Over light man has no 

 control. He can increase the amount of air that has access to 

 the plant by loosening the soil around its roots. An adaptive 

 control of heat is exercised by sowing during the warm season. 

 By selecting soils, fertilizing and changing existing foods from 

 unavailable to available forms, food can in a great measure be 

 regulated, and water, acting as a solvent and vehicle, can be 

 very largely regulated as to amount by drainage and irrigation. 

 That the growth and multiplication of cells involves a migra- 

 tion of material within the plant has long been recognized. In 

 wheat, as in many other plants, there is a comparatively large 

 development of roots soon after the first leaves appear. Only 

 some low-lying leaves are put forth while the great complex of 

 roots is being formed. In a wheat plant only 23 days old, the 

 roots had penetrated the soil over 1 foot in depth. When the 

 system of roots has been formed, the stalk suddenly shoots up 

 almost to mature stature. Perhaps the roots are completely 

 developed by the time that the formation of grain has begun. 

 The leaves of the wheat plant, with their chlorophyl cells, 

 have been considered as little laboratories elaborating vege- 

 table matter. Under the influence of light they are able to 

 extract carbonic acid from the atmosphere. This acid is one 

 of the raw materials of these little factories. They decompose 

 it, eliminate the oxygen, and from the residue they manufacture 

 sugar, cellulose, straw-gum, vasculose, and all the ternary mat- 

 ters composed of carbon, oxygen and hydrogen. A perfect sys- 

 tem of canals penetrates every part of the plant. These 

 canals are filled with water, which enters at the roots, for 

 leaves do not absorb water to any appreciable extent, and is 

 in constant motion until it is exhaled from the leaves. During 

 one hour of insolation a leaf of wheat exhales an amount of 

 water equal to its own weight. Upon these highways of 

 moving water are borne raw materials destined for the little 

 cell factories, such as nitrates, phosphoric acid, potash and 



