1. Hydrastis rhizome (Hydrastis canadensis, L.).
2. Musk root (Ferula sumbul, [Kauffm.] Hook., f.).
PLATE 44
Pitted Vessels
1. Quassia, low magnification (Picræna excelsa, [Swartz] Lindl.).
2. Quassia, high magnification.
3. White sandalwood (Santalum album, L.).
PLATE 45
Vessels
1. Reticulate vessel of calumba root (Jateorhiza palmata, [Lam.] Miers).
2. Reticulate tracheid of hydrastis rhizome (Hydrastis canadensis, L.).
3. Pitted vessel with bordered pores of belladonna stem.
4. Pitted vessel with bordered pores of aconite stem (Aconitum napellus, L.).
Vessels and tracheids lose their living-cell contents when fully developed. In the vessels the cell contents disappear at the period of dissolution of the cell wall.
The walls of vessels and tracheids are composed of lignin, a substance which prevents the collapsing of the walls when the surrounding cells press upon them, and which also prevents the tearing apart of the wall when the vessel is filled with ascending liquids under great pressure. Lignin thus enables the vessel to resist successively compression and tearing forces.
Tracheids are formed from superimposed cells with oblique perforated end walls. The side walls of tracheids are thickened in a manner similar to those of vessels. The tracheids in golden seal are of a bright-yellow color, and groups of these short tracheids scattered throughout the field form the most characteristic part of the powdered drug. In ipecac root the tracheids are of a porcelain-white, translucent appearance, and they are much longer than are the tracheids of golden seal.