26 



THE ESSENTIALS OF AGRICULTURE 



manganese occurs, but these elements are not considered essen- 

 tial to the life of plants. While only very small quantities of 

 some of these elements, such as iron and sulphur, are required, 

 any attempt to grow crops without them results in failure. All of 

 the elements, except carbon and a part of the oxygen, are ob- 

 tained by most plants from the soil alone, though some of the 



elements have come to the soil 

 from the air. A soil, therefore, 

 from which plants fail to secure 

 one or more of these elements 

 makes a poor farm. 



27. How plants get their 

 food. The raw food materials 

 in the soil must be dissolved in 

 water before the plants can take 

 them up through their roots. 

 Therefore the soil water serves 

 a double purpose as food for 

 the crop, and as a carrier of 

 other food elements. The roots 

 penetrate the soil in all direc- 

 tions, wherever there is air and 

 moisture (Fig. 14). The roots 

 of a corn or sunflower plant fill 

 a cubic yard of soil with tiny 

 rootlets. The roots produced in 

 a season by a wheat plant, if 

 placed end to end, would extend 

 a third of a mile. A pumpkin vine may produce fifteen miles 

 of roots in a season. 



28. The nature and extent of root hairs. The tiny rootlets do 

 not themselves absorb much water. This is done by minute 

 root hairs sometimes numbering 25,000 to the square inch of root 

 surface. These grow in feathery tufts near the tips of the small- 

 est rootlets. The root hairs begin as projections on the outside 

 cells of the rootlets (Fig. 1 5), at a point about a third of an inch 



FIG. 14. Root system of a corn 

 plant 



The roots spread and form an extensive 

 mat within the soil. The root hairs are 

 not shown in this picture. Note the 

 series of brace roots at , b, and c, those 

 at c not having reached to the soil 



