POROUS AND NON-STRIATED STONE CELLS 1. Ceylon cinnamon (_cinnamomum zeylanicum_, Nees). 2. Calumba root (_Jateorhiza palmata_, [Lam.] Miers). 3. Dogwood root bark (_Cornus florida_, L.). 4. Cubeb (_Piper cubeba_, L., f.) 5. Echinacea (_Echinacea angustifolia_, D.C.).] [Illustration: PLATE 34 1. Saigon cinnamon. 2. Ruellia root (_Ruellia ciliosa_, Pursh.). 3. Cascara sagrada (_Rhamnus purshiana_, D.C.). 4. Saigon cinnamon.] 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, they are 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 endodermal 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 referred to as a passage cell. The endodermal cells of triticum (Plate 35, Fig. 2) are yellowish, 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. The outer wall of the layer of cells is thinner than the inner wall. The innermost layer of cell is more uniformly thickened. [Illustration: PLATE 35 CROSS-SECTIONS OF ENDODERMAL CELLS OF 1. Sarsaparilla root (_Smilax officinalis_, Kunth). 2. Triticum (_Agropyron repens_, L.). 3. Convallaria (_Convallaria majalis_, L.). 4. Aletris (_Aletris farinosa_, L.).]