Mechanical Tissues. Stone Cells

Stone cells, like bast fibres, are branched or non-branched. Each group is then separated into subgroups according to wall structure (whether striated, or pitted and striated, etc.), thickness of wall and of cell cavity, color of wall and of cell contents, absence of color and of cell contents, etc.

Branched Stone Cells

Branched stone cells occur in a number of drugs. In witch-hazel bark (Plate 31, Fig. 2) the walls are thick, white, and very porous. In some cells the branches are of equal length; in others they are unequal. In the tea-leaf (Plate 31, Fig. 1) the walls are yellowish white and finely porous. When the lower wall is brought in focus, it shows numerous circular pits. These pits represent the pores viewed from the end. The branches frequently branch or fork.

Branched stone cells also occur in coto bark, acer spicatum, staranise, witch-hazel leaf, hemlock, and wild-cherry barks.

Non-branched stone cells are divided into two main groups, as follows:

1. Porous and striated stone cells, and,

2. Porous and non-striated stone cells.

Plate 31. Branched Stone Cells.

1. Tea leaf {Thea sinensis, L.).

2. Witch-hazel bark {Hamamelis virginiana, L.).

3. Hemlock bark (Tsuga canadensis, [L.] Carr).

4. Wild-cherry bark {Prunus serotina, Ehrh.).

Porous And Striated Stone Cells

Porous and striated walled stone cells occur in ruellia root, winter's bark, bitter root, allspice, and aconite. These stone cells are shown in Plate 33, Figs. 1,2, 3, 4, and 5.

The stone cells of ruellia root (Plate 32, Fig. 1) are greatly elongated, rectangular in form, with thick, white, strongly porous walls. The central cavity is narrow and is marked with prominent pores and striations.

The stone cells of winter's bark (Plate 32, Fig. 2) vary from elongated to nearly isodiametric. The pores are very large, the light yellowish wall is irregularly thickened, and the central cavity is very large. The pores are prominent.

The stone cell of bitter root (Plate 32, Fig. 3) is nearly isodiametric. The walls are yellowish white and strongly porous and striated. The central cavity is about equal to the thickness of the walls.

The stone cell of allspice (Plate 32, Fig. 4) is mostly rounded in form, and when the outer wall only is in focus it shows numerous round and elongated pores. The central cavity is filled with masses of reddish-brown tannin. The striations are very prominent.

The diagnostic stone cell of aconite (Plate 32, Fig. 5) is rectangular or square in outline; the walls are yellowish and the central cavity has a diameter many times the thickness of the wall. The side and surface view of the pores is prominent, and the striations are very fine.

Plate 32. Porous and Striated Stone Cells.

1. Ruellia root {Ruellia ciliosa, Pursh.).

2. Winter's-bark {Drimys winteri, Forst.)-

3. Bitterroot (Apocynum and rosaemifolium, L.).

4. Allspice (Pimenta officinalis, Lindl.).

5. Aconite {Aconitum napellus, L.).

Porous And Non-Striated Stone Cells

Porous and non-striated stone cells occur in Ceylon cinnamon, in calumba root, in dogwood bark, in cubeb, and in echinacea root.

The diagnostic stone cells of Ceylon cinnamon (Plate 33, Fig. 1) are nearly square in outline; the walls are strongly porous and the large central cavity frequently contains starch.

The stone cells of calumba root (Plate 33, Fig. 2) vary in shape from rectangular to nearly square, and the walls are greenish yellow, unequally thickened, and strongly porous. The typical stone cells contain several prisms, usually four.

The stone cells of dogwood bark (Plate 33, Fig. 3) have thick, white walls with simple and branched pores. The central cavity frequently branches and appears black when recently mounted, owing to the presence of air.

The stone cells of cubeb (Plate 33, Fig. 4) are very small, mostly rounded in outline, with a great number of very fine simple pores which extend from the outer wall to the central cavity. The wall is yellow and very thick.

The stone cells of echinacea root (Plate 33, Fig. 5) are very irregular in form; the walls are yellowish and porous, and the central cavity is very large. A black intercellular substance is usually adhering to portions of the outer wall.

The color of the walls of the different stone cells is very variable. In Ceylon cinnamon and ruellia the walls are colorless; in zanthoxylium, light yellow; in rumex, deep yellow; in cascara sagrada, greenish yellow.

The pores of stone cells, like the pores of bast fibres, are either simple or branched, and they may or may not extend through the entire wall. Many of the shorter pores extend for only a short distance from the cell cavity.

The width of the cell cavity varies considerably in the stone cells of the different plants. In aconite (Plate 32, Fig. 5), in calumba (Plate 33, Fig. 2), and in Ceylon cinnamon (Plate 33, Fig. 1), the cell cavity is several times greater than the thickness of the cell wall.

In allspice (Plate 32, Fig. 4), in bitter root (Plate 32, Fig. 3), the diameter of the cell cavity and the thickness of the wall are about equal. In cubeb (Plate 33, Fig. 4), in ruellia (Plate 32, Fig. 1), the wall is thicker than the diameter of the cell cavity.

The cavity of many stone cells contains no characteristic cell contents. In other stone cells the cell contents are as characteristic as the stone cell. The stone cells of both Saigon and Ceylon cinnamon (Plate 33, Fig. 1) contain starch; the stone cells of calumba (Plate 33, Fig. 2) contain prisms of calcium oxalate; the stone cells of allspice and sweet-birch bark contain tannin.

In cross-sections, stone cells occur singly, as in Saigon cinnamon (Plate 34, Fig. 1), ruellia (Plate 34, Fig. 2); in groups, as in cascara sagrada (Plate 34, Fig. 3); and in continuous bands, as in Saigon cinnamon (Plate 34, Fig. 4).

In powdered drugs, stone cells, like bast fibres, occur singly, as in ruellia, calumba, etc.; or in groups, as in cascara sagrada, witch-hazel bark, etc. In most powders they occur both singly and in groups.

The individual stone cells are mostly entire, as in ruellia, calumba, allspice, echinacea, etc. In cascara sagrada many of the stone cells are broken when the closely cemented groups are torn apart in the milling process. Many of the branched stone cells of witch-hazel bark and leaf, wild cherry, etc., also occur broken in the powder.

Plate 33. Porous and Non-Striated Stone Cells.

1. Ceylon cinnamon (cinnamomum zeylanicum, Nees).

2. Calumba root (Jateorhiza palmata, [Lam.] Miers).

3. Dogwood root bark {Cornus florida, L.).

4. Cubeb (Piper cubeba, L., f.)

5. Echinacea (Echinacea angustifolia, D.C.).

Plate 34.

1. Saigon cinnamon.

2. Ruellia root (Ruellia ciliosa, Pursh.).

3. Cascara sagrada (Rhamnus purshiana, D.C.).

4. Saigon cinnamon.

The walls of all stone cells are composed of lignin.

The form of stone cells varies greatly; in aconite the stone cells are quadrangular; in ruellia they are rectangular; in pimenta, circular or oval in outline; in most stone cells they are polygonal.

The lignified walls of stone cells are stained red with a solution of phloroglucin and hydrochloric acid, and the walls are stained yellow by aniline chloride.