PITTED VESSELS
Pitted vessels are met with most frequently in woods and wood-stemmed herbs. There are two distinct types of pitted vessels—i.e., simple pitted vessels and pitted vessels with bordered pores.
The pitted vessel represents the highest type of cell-wall thickening. The entire wall of the vessel is thickened, with the exception of the places where the pits occur. The number and size of the pits vary greatly in different drugs. In quassia (Plate 44, Fig. 1) the pits are numerous and very small, and the openings are nearly circular in outline. In white sandalwood (Plate 44, Fig. 3). the pits are few in number, but when they do occur they are much larger than are the pits of quassia.
PITTED VESSELS WITH BORDERED PORES
Pitted vessels with bordered pores are of common occurrence in the woody stems and stems of many herbaceous plants (Plate 45, Figs. 3 and 4). In such vessels the wall is unthickened for a short distance around the pits. This unthickened portion may be either circular or angled in outline, a given form being constant to the plant in which it occurs. The pits vary from oval to circular. Pitted vessels with bordered pores occur in belladonna and aconite stems.
PLATE 42
Sclariform Vessels
1. Sarsaparilla root (Smilax officinalis, Kunth).
2. Male fern (Dryopteris marginalis, [L.] A. Gray).
3. Tonga root.
PLATE 43
Reticulate Vessels