116 HISTOLOGY OF MEDICINAL PLANTS 
stone cells of witch-hazel bark and leaf, wild cherry, etc., also 
occur broken in the powder. 
The walls of all stone cells are composed of lignin. 
The form of stone cells varies greatly; in aconite the stone 
cells are quadrangular; in ruellia they are rectangular; in 
pimenta, circular or oval in outline; in most stone cells they 
are polygonal. 
The lignified walls of stone cells are stained red with a 
solution of phloroglucin and hydrochloric acid, and the walls 
are stained yellow by aniline chloride. 
ENDODERMAL CELLS 
The endodermal cells of the different plants vary greatly 
in form, color, structure, and composition of the wall, yet these 
different endodermal cells may be divided into two groups: 
first, thin-walled parenchyma-like cells, and, secondly, thick- 
walled fibre-like cells. In the thin-walled endodermal cells the 
walls are composed of cellulose, and the cell terminations are 
blunt or rounded. When the drug is powdered the cells break 
up into small diagnostic fragments. In the thick-walled endo- 
dermal cells the walls are lignified and porous, and the ends of 
the cell are frequently pointed and resemble fibres. 
Sarsaparilla root, triticum, convallaria, and aletris have 
thick-walled endodermal cells. 
STRUCTURE OF ENDODERMAL CELLS 
The endodermal cells of sarsaparilla root (Plate 35, Fig. 1) 
are never more than one layer in thickness. The walls are 
porous and of a yellowish-brown color. Alternating with the 
thick-walled cell is a thin-walled cell, which is frequently re- 
ferred to as a passage cell. 
The endodermal cells of triticum (Plate 35, Fig. 2) are yellow- 
ish and the walls are porous and striated. There are one or two 
layers of cells. The cells forming the outer layer have very 
thin outer but thick inner walls, while the cells forming the 
inner layer are more uniform in thickness. 
The endodermal cells of convallaria (Plate 35, Fig. 3) are 
yellowish white in color, and the walls are porous and striated. 
