90 CIRCULATION AND USES OF PLANT FOOD 



where (in young specimens) they may be followed as veins. The 

 outside of the corn stem is formed of large numbers of fibrovascular 

 bundles, which, closely packed together, form a hard, tough outer 

 rind. Thus the woody material on the outside gives mechanical 

 support to an otherwise spongy stem. 



Comparison in the Growth of a Dicotyledonous and a Monocoty- 

 ledonous Stem. — In a young dicotyledonous stem, cut in cross 



Phloem 

 Cambium 

 layer 

 Xylem 



Food made in 

 leaves passes 

 down fhrough 

 — the inner bark 



Materials taken 

 in by roof pass 

 up the stem in 

 this region 



Diagram to show the areas in a plant through which the raw food materials pass 

 up the stem and food materials pass down. 



section, the woody bundles are arranged as a ring near the outer 

 edge of the stem (see figure). These bundles grow both toward 

 the outside and toward the center of the stem from an actively 

 dividing layer of cells. This layer in older stems becomes a com- 

 plete ring under the bark and is called the cambium layer. On the 

 outside of the cambium layer is found the phlo'em, or portion con- 

 taining the sieve tubes which bear elaborated food toward the 



