74 HISTOLOGY OF MEDICINAL PLANTS 
number of uniseriate-arranged cells of unequal length, frequently 
placed at right angles to the cells above and below; the walls 
are of a whitish color, and are rough or smooth. 
Eastern skullcap (Plate 9, Fig. 4) has hairs with not more 
than four cells; these hairs are curved, and the walls are whitish, 
sometimes smooth, but usually rough. In Western skullcap 
(Plate 9, Fig. 3) the hairs have sometimes as many as seven 
cells. The walls are white and rough, and the individual cells 
of the hair are much larger than are the cells of the hairs of 
true skullcap. 
Peppermint (Plate 9, Fig. 5) has from one to eight cells. 
The hair is curved, and the walls are very rough. 
Thyme (Plate 9, Fig. 6) has short, thick, rough-walled 
trichomes, the terminal cell usually being bent at nearly right 
angles to the other cells. 
Yarrow hairs (Plate 9, Fig. 7) have a variable number of 
cells. In all the hairs the basal cells are short and broad, while 
the terminal cell is greatly elongated. 
Arnica hairs (one form, Plate 9, Fig. 2) have frequently as 
many as four cells, the terminal cell being longer than the basal 
cells. The walls are white and smooth. 
Sumac-fruit hairs (Plate 9, Fig. 9) have spindle-shaped, 
reddish-colored hairs. 
Multicellular multiseriate non-branched hairs occur on 
cumin fruit and on the tubular part of the corolla of calendula. 
The hairs on cumin fruit vary considerably in size. All the 
hairs are spreading at the base and blunt or rounded at the apex. 
The cells forming the hair are narrow and the walls are thick. 
Three differently sized hairs are shown in Plate to, Fig. 1. 
The hairs of the base of the ligulate petals of calendula 
(Plate 10, Fig. 2) are biseriate. The hairs are very long and 
the walls are very thin. 
Multicellular uniseriate branched hairs occur on the leaves 
of dittany of Crete, mullen, and on the calyx of lavender flowers. 
The dittany of Crete (Plate 11, Fig. 3) hair is smooth-walled, 
and the branches are alternate. 
In mullen (Plate 11, Fig. 1) the hairs have whorled branches, 
the walls are smooth, and the cell cavity usually contains air. 
The lavender hairs (Plate 11, Fig. 2) have mostly opposite 
