STEMS 241 
field; the glandular hairs (5) with a two-celled stalk; the eight- 
celled glandular hair (7) seen in surface view and a side view (8) 
of a similar hair; the long, pointed, unicellular non-glandular 
hair from the tube of the corolla, the wall irregularly thickened 
near the apex; the fibres (9g) from the stem; the pollen grains 
(z0) with prominent centrifugal projections; the conducting 
cells. 
The diagnostic elements of marrubium perigrinum are the 
multicellular branched hairs (3) which occur on all parts of the 
plant, usually much broken in the powder, with walls many 
times thicker than the walls of the hairs found in U. S. P. hore- 
hound; the pollen grains (10) with centrifugal projections and 
the stalked glandular hairs (5). 
INSECT FLOWER STEMS 
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. 
