80 HISTOLOGY OF MEDICINAL PLANTS 
branches (Plate 14, Fig. 2) are much longer than special 
branches. 
The hair of grindelia (Plate 14, Figs. 3 and 4) has very thick 
walls with numerous elongated pores. The apex of the hair 
terminates in a cluster of cells with short, free, sharp-pointed 
ends. The basal branches (Plate 14, Fig. 4) are longer than 
the apical branches. 
Boneset hair (Plate 15, Figs. 1 and 2) has non-porous walls. 
The apex of the hair terminates in two blunt-pointed cells. 
The terminal wall is thicker than the side wall. Some of the 
branches lower down terminate in cells with very thick or solid 
points. The basal branches (Plate 15, Fig. 1) are longer, but 
the cells are narrower and more strongly tapering than are the 
branches of the apical part of the hair. 
Life-everlasting (Plate 15, Figs. 3 and 4) has uniformly 
thickened but non-porous walls. The hair terminates in two 
blunt-pointed, greatly elongated cells. 
The basal branches (Plate 15, Fig. 4) are narrower, slightly 
tapering, and the base of the branches frequently curve down- 
ward. 
The cell cavities of these hairs are filled with air. 
The walls of hairs are usually composed of cutin; in some 
hairs, of lignin; in other hairs, of cellulose. 
PERIDERM 
The periderm is the outer protective covering of the stems 
and roots of mature shrubs and trees. The periderm replaces 
the epidermis. The periderm may be composed of cork cells, 
stone cell-cork, or a mixture of cork, parenchyma, fibres, stone 
cells, etc. 
CORK PERIDERM 
The typical periderm is made up of cork cells. Cork cells 
vary in appearance, according to the part of the cell viewed. 
On surface view (Plate 16, Fig. A) the cork cells are angled 
in outline and are made up of from four to seven side walls; 
five- and six-sided cells are more common than the four- and 
seven-sided cells. Surface sections of cork cells show their 
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