Quite a number of drugs consist of the wood of woody plants; such drugs are quassia, red saunders, white sandalwood, and guaiac.

When studying woods it is necessary to observe the cross, tangential, and radial sections. Such sections of quassia are shown in Plates 105, 106, and 107. When studying these sections it should be remembered that while the types of cells forming quassia wood are similar to the cells forming other woods, still their structure, arrangement, and amount will vary in a recognizable way in the different woods.

Cross-Section Quassia

Plate 105 is a cross-section of quassia. It has the following structure:

Vessels

The vessels occur singly or in groups of two to eight cells. The cells are variable in size and shape. The walls are yellowish white and porous.

Medullary Rays

The medullary rays vary from one to five cells in width.

The medullary ray cells are radially elongated and the walls are strongly porous.

Wood Parenchyma

The wood parenchyma cells have thin, yellowish-white, angled walls.

Wood Fibres

The wood fibres have thick, yellowish-white, angled walls. These cells are smaller in diameter than the wood parenchyma cells.

Plate 105. Cross-Section of Quassia Wood (Purana excelsa [Sw.], LIndl.).

1. Vessels.

2. Medullary rays.

3. Wood parenchyma.

4. Wood fibres.

Radial Section Quassia

The radial section of quassia (Plate 107) is as follows: Vessels. The vessels appear as in the tangential section. Medullary rays. The medullary rays vary from ten to twenty cells in height according to the part of the medullary ray bundle cut across.

The medullary ray cells exhibit their height and length. The walls of the cells are yellowish white and strongly porous.

Wood Parenchyma

The wood parenchyma cells have yellowish, thin walls and blunt end walls.

Wood Fibres

The wood fibres have thick, yellowish-white walls, and the end of the cells are strongly tapering.

Plate 107. Radial Section of Quassia Wood {Picraena excelsa [Sw.] Lindl.).

1. Showing the height and length of the medullary rays and cells.

2. Cells with starch.

3. Wood parenchyma and wood fibres.

Tangential Section Quassia

The tangential section of quassia (Plate 106) shows the following structure:

Vessels

The vessels are very long and broad and the yellow walls are marked with clearly defined pits.

Medullary Rays

The tangential section shows the cross-section of the medullary ray bundle and the cross-section of the medullary ray cell.

The medullary ray bundle varies in width from one to five cells. The ends of the bundles are always one cell in width, while the central part of the bundle is frequently five cells in width.

The medullary ray cell varies in size, structure, and shape according to the part of the cell cut across. The cells cut across the centre show hollow spaces, but the cells cut just above or below the end wall show a strongly pitted surface. The cells forming the end of the bundle are larger than the cells forming the centre of the bundle.

Wood Parenchyma

The wood parenchyma cells are greatly elongated and the walls are thin and yellowish white. The ends of the cells are blunt.

Wood Fibres

The wood fibres are elongated, the walls are thick and the cells are strongly tapering.

In quassia, white sandalwood, red sandalwood, and guaiac wood are characteristic crystals.

In quassia the vessels are finely pitted, yellowish, and distinct; in white sandalwood the vessels are coarsely and sparingly pitted and white translucent; in red saunders the vessels are coarsely pitted, bright red and distinct.

When studying woods we must consider the width of the medullary rays, the structure and cell contents of the medullary ray cells; the structure, color, and cell contents of the wood parenchyma; also the wood fibres.

Plate 106. Tangential Section of Quassia Wood (Picrcena excelsa [Sw.], Lindl.).

I. Vessel. 2. Wood parenchyma. 3. Wood fibre. 4. End wall of medullary ray cell. 5. Medullary ray bundle.