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, i 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. i) 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 composed of cutin, of lignin, and 

 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 



