PLATE 124
Cross-Section of a Radial Vascular Bundle of Skunk Cabbage Root
(Symplocarpus fœtidus [L.], Nutt.)
1. Vessels.
2. Bundle sheath.
3. Parenchyma.
4. Sieve cells.
PLATE 125
Cross-Section of a Phloem-Centric Bundle of Calamus Rhizome (Acorus calamus, L.)
1. Vessels.
2. Sieve cells.
3. Phloem parenchyma.
4. Parenchyma surrounding the bundles.
In sarsaparilla root, the pith is composed of thick-walled, porous pith parenchyma cells with starch. Outside the pith are arranged radial bands of oval vessels which decrease in size toward the periphery. Between the ends of these bands occur isolated groups of sieve cells.
Surrounding the sieve cells and vessels are thick-walled, angled fibres.
External to these cells is an endodermis composed of lignified brownish-colored cells one layer in thickness.
CONCENTRIC VASCULAR BUNDLES
There are two principal types of the concentric bundle, namely, xylem-centric, in which the xylem is centric and the phloem is peripheral, as in veratrum root; and phloem-centric (Plate 125), in which the phloem is centric and the xylem peripheral, as in calamus rhizome.