Epidermis. The epidermal cells are small, nearly as long as broad, and the outer wall is thicker and darker in color than the side and inner walls. The cells usually contain air.
Cortex. The cortical parenchyma cells are very large and somewhat rounded in outline, and the walls are white. There are about twelve rows of these cells, and each cell contains numerous small, rounded starch grains.
Endodermis. The endodermal cells are tangentially elongated, and the walls are very thin and white. There are two or three layers of endodermal cells; the cells’ outer layers are larger than the cells of the inner layers.
PLATE 89
Cross-section of Root of Spigelia marylandica, L.
1. Epidermis. 2. Cortical parenchyma. 2´. Intercellular space. 3. Endodermis. 4. Pericycle. 5. Cambium. 6. Xylem. 7. Pith.
Pericycle. The cells forming the pericycle are sieve cells and phloem parenchyma. The sieve cells are small, angled cells with extremely thin, white walls.
The phloem parenchyma resemble the sieve cells, except that they are larger.
Cambium. The cambium cells are rectangular in shape; the walls are thin and white.
Xylem. The xylem is composed of tracheids, wood parenchyma, and wood fibres.