PLATE 101
A. Cross-section of buchu stem (Barosma betulina [Berg.], Barth. and Wendl.). 1, Outer wall of epidermis; 2, Cell cavity of epidermal cell; 3, Wall of cork cell; 4, Cavity of cork cell; 5, Phellogen layer; 6, Divided phellogen cell changing into a cortical parenchyma cell; 7, Cortical parenchyma cell.
B. Cross-section of leptandra rhizome (Leptandra virginica [L.], Nutt.). 1, Parenchyma cells undergoing change in the composition of their walls; 2, A break in the epidermal tissue; 3, Parenchyma cells undergoing division.
POWDERED BUCHU STEM
Powdered buchu stem (Plate 102) has many striking features which make it easy of identification when mixed with buchu leaves. A few unicellular, rough, thick, white-walled trichomes (1) occur distributed throughout the field. They are straight or slightly curved and vary in length from 40 to 100 microns; in thickness at the bast they measure from 10 to 22 microns. The central cavity varies greatly, and in some trichomes seems to have disappeared entirely. The epidermal cells (2) are very characteristic, occurring singly or in groups of two or more. The cells from the older stems often appear reddish brown by transmitted light, while the epidermal cells from the younger stems appear whitish opaque (porcelain-like). They are usually six-sided and angular in outline. The cortical parenchyma cells (3) on transverse view have a rounded cell cavity and intercellular spaces between the walls. The double walls vary in thickness, the greatest thickness being about 9 microns. The parenchyma cells (3) on longitudinal view show square ends and often contain sphæro-crystalline masses of hesperidin. The thin-walled sieve cells and the surrounding cells are scarcely ever seen in the powder. The white-walled pointed stereomes (4) are a characteristic feature of the powder; they vary greatly in length, in diameter and in the thickness of their walls. In a number eighty powder the fibres are mostly broken. The greatest length of the unbroken fibres is 1.25 microns. The thickest wall measured 5 microns and the greatest observed width was 25 microns. The spiral reticulate and scalariform thickened conducting cells occur scattered throughout the powder. The reticulate and scalariform cells usually occur with wood fibres. It is an interesting fact that the spiral thickening in conducting cells is usually separate from the side wall and nearly always appears as indicated at 5. An occasional rosette crystal of calcium oxalate (6) is seen in the field. The wood parenchyma (7), which makes up a very small percentage of the xylem, is not readily found in the powder. The pith parenchyma cells (8) have thick, porous side walls and perforated side walls. The wood fibres (9) usually occur in masses surrounding the conducting cells; when occurring singly, the oblique pores readily distinguish them from the bast fibres.
PLATE 102
Powdered Buchu Stems
(Barosma betulina [Berg.], Barth. and Wendl.).
1. Hairs. 2. Epidermal cells, the larger pieces reddish-brown; the smaller aggregations white. 3. Transverse cortical parenchyma. 3’ Longitudinal cortical parenchyma with sphæro crystalline masses of hesperidin. 4. Bast fibres. 5. Spiral, sclariform, and reticulate vessels. 6. Rosette crystals of calcium oxalate. 7. Wood parenchyma. 8. Pith parenchyma with porous side and end walls. 9. Wood fibres.
The diagnostic elements of powdered buchu stems are:
First, trichomes; secondly, reddish-brown and white-angled epidermal cells; thirdly, the long, white bast fibres.