In soap bark (Plate 26, Fig. 1) the bast fibres have thick, white, wavy walls and a narrow cavity. One end of the cell is frequently somewhat blunt while the opposite end is slightly tapering.
The branched stone cells of wild-cherry bark have three or more branches. The pores are small and usually non-branched, and the striations are very fine and difficult to see unless the iris diaphragm is nearly closed. The central cavity is very narrow and frequently contains brown tannin.
The branched stone cells of hemlock bark are very large; the walls are white and distinctly porous bordering on the cell cavity, which contains bright reddish-brown masses of tannin.
In cross-section bast fibres occur singly or isolated, as in Saigon cinnamon (Plate 34, Fig. 1); or in groups, as in menispermum (Plate 27, Figs. 1 and 2); or in the form of continuous bands, as in buchu stem (Plate 100, Fig. 5).
Bast fibres are seen in longitudinal view in powdered drugs. The cell cavity shows throughout the length of the fibre. This cavity differs greatly in different fibres. In soap bark (Plate 26, Fig. 1) there is scarcely any cell cavity, while in mezereum bark (Plate 26, Fig. 4) the cell cavity is very large.
1. Soap bark (_Quillaja saponaria_, Molina). 2. Ceylon cinnamon bark (_Cinnamomum zeylanicum_, Nees). 3. Sassafras root bark (_Sassafras variifolium_, [Salisb.] Kuntze). 4. Mezereum bark (_Daphne mezereum_, L.).]
1. Menispermum rhizome (_Menispermum canadensis_, L.). 2. Althea root (_Althæa officinalis_, L.) showing two groups of bast fibres.]
The pores, which are absent in many drugs, are, when present, either simple, as in echinacea root (Plate 24, Fig. 4), or they are branched, as in yellow cinchona (Plate 23, Fig. 3).
In each of the above fibres the length and width of the fibre are shown. The fibres also have pores of variable length. Such a variation is common to most fibres with pores. That part of the wall immediately over or below the cell cavity shows the end view or diameter of the pore, as in the fibre of marshmallow root (Plate 24, Fig. 3). As a rule, however, the pores show indistinctly on the upper and lower wall.
In powdered drugs bast fibres occur singly or in groups. The individual fibres may be broken, as in mezereum and elm bark, or they may be entire, as in Ceylon cinnamon and in sassafras bark (Plate 26, Figs. 2 and 3).