THE STEM 47 
thin transverse section of the stem of the sunflower 
and examine it under the microscope we note a resem- 
blance between it and the transverse section of the root 
mentioned in par.21. We have again a central cylinder 
containing a number of vascular bundles and surrounded 
by a parenchynratous tissue (fig. 30). 
The outermost layer of cells is the epidermis. It is com- 
posed of strong cells often covered with a protective layer 
of cutin and they serve to protect the inside tissues of the 
Fig. 30.—Transverse Section of Stem ot a Dicotyledon. 
A. Young stem. M. Pith. 2. Xylem. p. Phloem. R. Cortex. B. 
Older stem; bundles now united by interfascicular cambium (ic). 
fe. Cambium of the primary bundle. 6. Primary bast fibres 
(diagrammatic). 
stem. Next comes the cortex, a tissue similar to the cor- 
tex of the root. The innermost ring of cortex cells forms 
the endodermis. It usually contains starch and shows up 
well asa blue wavy line in a section stained with iodine. 
Inside the endodermis comes a ring of vascular bundles. 
The space between each bundle is filled with parenchy- 
matous tissue, and is called the Primary MEDULLARY 
Ray. The interior is filled with a mass of pith cells 
similar to those found in the root. In a young stem 
these pith cells are soft, green, and juicy. In an older 
