48 AGRICULTURE 



branch and subdivide into smaller roots, rootlets, and root hairs. 

 Cereals and grasses are fibrous-rooted plants. Sometimes fibrous 

 roots enlarge and store up sugar and starch. Sweet potatoes, 

 for instance, are enlarged fibrous roots. 



Weak- and Strong-Feeding Plants. Roots differ greatly in 

 their power to take in food from the soil. Some plants c.re very 

 weak feeders. For them to thrive, the soil must be carefully pre- 

 pared, and food must be near in available form. Strong-feeding 

 plants have much greater power to collect food and require less 

 care, though no agricultural plant will thrive on neglect. Wheat 

 is a weak feeder and corn is a strong feeder, belonging to the same 

 great family of cereals, or grain plants. 



Stems. The stem bears the branches, with the leaves, blos- 

 soms, and seeds. It is the channel for the sap. Stems vary greatly 

 in appearance. Usually, as in the case of the cotton plant, they 

 are stiff enough to hold the plant upright. Vines, such as the grape- 

 vine and ivy, have stems which climb on some support. Melons, 

 such as the watermelon, have prbs'trate stems, which lie upon the 

 ground. Sometimes the stem, or a part of it, grows underground. 

 This is the case with Bermuda grass. The white, or Irish, potato is 



an enlargement of an underground stem. 

 Parts of Stem. In most stems there 

 are a woody, fibrous matter, a cambium, 

 or inner bark, and a thick outer bark. 

 In the center of the stem of long-lived 

 perennial trees there is a layer of old 

 A white potato -an enlarged tissue, or heartwood, through which 



underground stem . 



there is little movement of sap. 



Girdling Plants. If a plant is girdled, or has its outer bark 

 and cambium cut off all around, the top does not wither and die 

 at once, as it does if its roots are cut. Sap still mounts upward 



