8 THE WHEAT INDUSTRY 



leaves and head in the air and sunshine. It also 

 serves as a passageway to transfer food materials 

 from the roots to other parts of the plant. The 

 upper part of the stem remains green until late 

 in the period of ripening and seems to do work 

 similar to that of the leaves in manufacturing 

 food for the grain. 



The Leaves. - -The leaves are long, slender blades 

 growing from the stem. They are close together 

 on young plants and become farther apart as the 

 joints of the stem lengthen during growth. The 

 leaves are small workshops as well as breathing 

 machines, and do a very important work for the 

 plant. They are filled with small canals through 

 which solutions flow, and the surface has innu- 

 merable pores which admit air. Moisture and 

 food material are transferred from the roots to the 

 leaves, and gases are taken directly from the air. 

 Within the leaves, with the aid of sunlight, these 

 food materials, gases, and moisture are combined 

 and changed into food substances such as starch, 

 sugar, and cellulose. The leaf products are carried 

 to the heads of the plant and built into fruit or 

 grain. With abundance of moisture and a rich 

 soil these processes make rapid progress with the 

 result that the plant acquires strong growth and 

 produces a heavy yield. If moisture is lacking 

 or the soil is weak, the work goes on more slowly or 

 for a shorter period. The lower leaves soon be- 



