Insect flower stems are the chief adulterant of insect flowers. Until the passage of the insecticide law, it was a common practice to sell (for insect powder) a mixture of powdered stems and flowers. Since the passage of the law, the presence of the stems in a powder is supposed to be declared on the label. In spite of the penalties attached, their presence in a powder is frequently not declared, as evidenced by a microscopical examination of the insect powders obtained in the open market. The structure of powdered insect flower stems (Chart 99) is as follows: The epidermal cells of the stems are prominently marked with stoma and angled, striated wall cells (Fig. 1). On cross-section (Fig. 2) the stem is seen to be made up of epidermal cells with thick outer and thin side walls (Fig. 2). The T-shaped hairs (Fig. 3) are longer than those found on any other part of the plant. The fibres (Fig. 4) are the most characteristic part of the powder. They are elongated, and the walls are white and slightly porous and of nearly uniform thickness. They occur free in the field or in groups of two or more. The cross-section view of these fibres is shown in Fig. 5. The pith parenchyma (Fig. 6) is abundant and is composed of thick, porous-walled cells. On cross-section the cells are rounded and are separated by intercellular spaces. The conducting cells (Fig. 8) vary from spiral to reticulate. CHAPTER III WOODY STEMS BUCHU STEM The cross-section of a buchu stem (Plate C), 1.6 millimeters in diameter, shows a few of the epidermal cells modified into thick-walled, roughish, unicellular trichomes (1). The remaining epidermal cells have a thick, wavy outer wall (2). Beneath the epidermis are several rows of cortical parenchyma cells (3) which extend to the bast bundles and in which are found the secretory cavities with the thin-walled secretory cells (4). The bast fibres (5) occur in continuous bands, varying greatly in size; the walls are whitish and of variable thickness. Inside the bast fibres, the small irregular sieve cells (6) occur in groups, surrounded by the phloem parenchyma (8). The radially elongated cells of the medullary rays (7) extend outward from the xylem, increasing in number in the outer portions of the wood, and extending nearly to the bast fibres. No distinct cambium layer is visible. The conducting cells (9) occur throughout the xylem surrounded by the wood fibres and wood parenchyma (10). The latter is not very abundant in buchu. The medullary rays border on the conducting cells and extend outward to the phloem. The pith parenchyma cells are nearly circular in outline and often show a perforated end wall when a cell happens to be cut just above or below that point. MATURE BUCHU STEM