438 PLANTS AND THEIR RELATION TO MAN 



The soil as a source of plant food. Plants, like other 

 living organisms, require food for existence and growth, and 

 they obtain food from two sources, the soil and the air. From 

 the soil the roots take water containing dissolved mineral 

 and organic matter. The soil water absorbed by the root 

 rises through the stem and makes its way to all parts of the 

 plant. The leaves take carbon dioxide from the air. The 

 carbon dioxide combines with the water and forms starch and 



sugar. Both soil food and air food are 

 essential to plant life, because if either 

 is lacking, the plant droops and dies. 

 If the farm soil is poor and lacks plant 

 nourishment, the crops starve. The 

 wise farmer always keeps his soil rich 

 in plant foods by fertilizer, that is, he 

 puts into the soil substances which he 

 knows the plant needs. 



How soil food gets into the plant. 

 The soil is a storehouse of water and 

 food for the plant. Water, holding 

 dissolved soil food, enters the plant not 

 through the roots, but through small 

 hairs called root hairs. The delicate 

 root hairs grow only on the tender 

 young roots or rootlets, a short distance 



back from their tips (Fig. 306). When the rootlets grow into 

 roots, they lose their root hairs, but they send off new rootlets 

 on which root hairs quickly form. The root hairs absorb mois- 

 ture through their thin delicate walls. A transplanted bush 

 wilts and droops for a long time, because no matter how care- 

 fully it is removed from the soil, some of its rootlets are torn 

 off or injured and the water and food supply are lessened. As 

 soon as iew rootlets and new root hairs develop on the trans- 



FIG. 306. Root hairs (R.H.) 

 on sprouting corn. 



