ARRANGEMENT OF THE VASCULAR BUNDLES 267 
cell is long and pointed. Some of these cells overlap in such 
a way that they make continuous tubes from the root, up 
through the stem, and into the leaves. The thick walls help 
to give firmness to the plant. 
The phloem cells are the other part of the vascular bundle 
in a monocotyledonous stem. They have thinner walls than 
the xylem cells and they communicate with one another 
through the ends and not 
through the sides. The 
ends of these cells have 
perforated plates through 
which the liquid in the 
cells passes. These are 
called sieve plates. 
In a dicotyledonous 
stem, the vascular bun¬ 
dles are made up of three 
kinds of elements, the 
phloem, like that of the 
monocotyledonous stem, 
and the xylem, also like 
that already described. 
Between them is a layer 
of thin-walled, brick¬ 
shaped cells called cam¬ 
bium where growth is 
taking place rapidly. This is the cambium or meristem 
tissue. The side towards the phloem is constantly produc¬ 
ing phloem cells, and the other side xylem cells. Associated 
with the phloem cells are bast fibers, the function of which 
is to give strength and firmness to the stem. 
235. Arrangement of the Vascular Bundles. — This differs in 
the two kinds of stems already mentioned. In the corn stalk, 
a monocotyledonous stem, the vascular bundles are scattered 
throughout the central pith, and the bundles have no definite 
Figure 255. — Cross Section of Corn 
Stem. 
Note the fibro-vascular bundles scattered 
throughout the pith. 
