188 STEMS 
as to form distinct regions, such as pith, vascular cylinder, and 
cortex, which are more or less distinct regions in Dicotyledons.. 
When cross sections of the Corn stem are studied with the 
microscope, such anatomical features as shown in Figure 166 
may be seen. The cells of the rind are rectangular in shape, con- 
sist of a number of rows, and their walls are thickened and made 
woody for strength. The woody feature of the rind is character- 
istic of Grasses and Sedges, being much less prominent in other 
monocotyledonous stems, as, for example, in Lilies and Aspara- 
gus. The outer row of cells of 
the rind constitute the epider- 
we AW mis, although in the Grasses the 
jase i epidermal cells differ very little 
SE from other rind cells, except that 
they have silica and cutin de- 
posited in their outer walls. 
The vascular bundles, contain- 
ing numerous cells, show three 
or four large openings which are 
the large vessels of the xylem. 
Besides the large size of the pith 
ee ee ee cells as shown in the drawing, 
section of a Corn stem much en- Other features not shown, such 
larged. a, epidermis; b, thebandof as their storage function and 
strengthening cells under the epider-_ their being so loosely joined as 
mis and often called cortex; v, vascu- to form a spongy filling for the 
lar bundles; e, pith. After Stevens. stem, should be mentioned. 
To study the complex structure of a vascular bundle, we must 
turn to a more highly magnified cross section of the bundle as 
shown in Figure 167. The vascular bundle consists of strength- 
ening and conductive tissues, the latter of which is composed 
of the xylem and phloem,—the chief structures of all vascular 
bundles. In respect to the character of the vessels composing 
them, xylem and phloem show much uniformity throughout Flow- 
ering Plants. 
In the xylem the conductive tissues consist mainly of large ves- 
sels, known as spiral, annular, or pitted vessels according to the 
character of the thickenings in their walls, as partly shown in Fig- 
ure 168 and more fully shown in Figure 169. The woody thicken- 
ings, which strengthen the cellulose walls of the vessels so that 
