268 
STEMS 
position with reference to the center. The outside of the 
stem is covered with a hard rind which often contains silica, 
a substance like glass which makes it hard and strong. In 
grasses, the stem is hollow, and the bundles are of course 
around the edges, some of them 
passing off at each node into the 
leaf which arises from it. 
Figure 257. — Part of Cross 
Section of Young Dicotyle¬ 
donous Stem. 
Figure 256. — Corn 
Stem, Broken. 
A, node; B, hard 
outer rind; C . pith; 
D, fibro-vascular bun¬ 
dles. 
Note the arrangement of the 
fibro-vascular bundles. These 
gradually form a complete ring. 
The cambium layer in an older 
stem lies under the bark. Its 
color is green. 
236. The Work of the Vascular Bundle. — We have said that 
the vascular bundles are a part of the conductive system of a 
plant, and that some of the cells form vessels. There is little 
likeness to the vascular system of animals, however, for the 
system in plants lacks an organ for driving the liquid in the 
tubes, and it has little use as an aid to respiration. Water, 
