MAIZE OR INDIAN CORN 153 



192. Structure of roots. A young feeding root is 

 made up of four different parts as follows: (1) The epider- 

 mis or "piliferous layer" composed of a single layer of 

 cells which forms the outermost layer of the root. From 

 these epidermal cells the root-hairs develop. This layer 

 together with the root-hairs is really the absorbing surface 

 for food and moisture. (2) A rather thick layer of thin- 

 walled cells lying just inside the epidermis and known as 

 the cortex. This layer corresponds to the bark on a stem. 

 (3) The endodermis which is really the innermost layer of 

 the cortex cells. This layer is differentiated by thicker 

 walls to form a definite sheath, the probable function of 

 which is to prevent the escape of plant-food on its upward 

 course through the central column of the root. (4) The 

 central cylinder which is a columnar mass of cells com- 

 prising the central portion of the root through which the 

 plant-food is carried upward to the stem and leaves. 



193. Adventitious roots. During the latter part of 

 the growing period, corn often puts out roots at the first 

 two or three nodes above the surface of the soil. These 

 roots are termed "brace roots" or "prop roots" because 

 they serve to brace the plant against wind. In the air 

 these roots are, as a rule, unbranched, but they branch 

 rather profusely after entering the soil and in addition 

 to bracing the plant, they take up moisture and food. 



194. Stems. The stem of corn is more variable in 

 size and height than that of any other cereal. In some 

 varieties of pop-corn the stems or culms will not average 

 over 20 inches high. In the West Indies, corn often grows 

 to a height of 30 feet or more. From 5 to 10 feet is the 

 average variation in the United States. Soil, climate and 

 variety are the important factors that determine the height 

 of corn plants. In the northern latitudes of the United 



