1. Short, broad cystoliths from the rhizome, 1´. Long cystoliths from the root. 2 and 2´. Long, narrow, white-walled bast fibres. 3. Tracheal tissue from the xylem of the stem. 4. Root parenchyma. 5. Tracheal tissue from the xylem of the root. 6. Cortical parenchyma cells from the rhizome with short, broad cystoliths. 7 and 7´. Long, thick-walled sclerids from the root. 8. Short, broad sclerids from the stem. 9. Pitted pith parenchyma from the stem with intercellular space. 10. Parenchyma of the root with sclerid and cystolith, longitudinal view.] The epidermal cells vary from 7.8 by 15.6 micromillimeters to 15.1 by 16.6 micromillimeters. The cell contents are dark and the walls are light. A few rows of the outer cortical parenchyma cells of both the rhizome and the root have dark cell contents and white walls. The dark contents disappear toward the phloem. The cortical cells vary from 13.6 by 14.3 micromillimeters to 89.5 by 90.9 micromillimeters. In the cortical parenchyma cells of the rhizome are found the short, broad cystoliths measuring up to 52 by 62 micromillimeters. In the corresponding cells of the root are found the long, narrow cystoliths which measure up to 68.4 by 187.2 micromillimeters. Scattered throughout the powder are seen three distinct types of sclerids (stone cells) which are associated with the cortical parenchyma of both the stem and the root. Most of them are found, however, in the roots. First, the short, broad stone cells from the stem basis have square ends; the walls vary from 13 to 19.5 micromillimeters in thickness with branching pores which extend toward the adjacent cell. These sclerids vary in size from 52 by 54.6 micromillimeters to 45 by 130 micromillimeters. Secondly, the long stone cells from the root vary from 32 by 96 micromillimeters to 45.5 by 542.5 micromillimeters with walls 16 micromillimeters thick. The width of the cell and the thickness of the wall vary but little throughout their entire length. The third type of stone cell also from the root has unequally thickened walls and the ends are square or blunt. A few long, narrow, colorless, thin-walled bast fibres also occur. They are 13 micromillimeters wide, with walls 3.9 micromillimeters thick. Annular spiral and pitted vessels are also found scattered throughout the powder. The diagnostic characters of the powder are: 1. The short, broad, and long, narrow cystoliths. 2. The short, broad, and long, narrow sclerids. 3. The long, narrow, thin, white-walled bast fibres. In poke root, ipecac, sarsaparilla, and veratrum are raphides. In belladonna and horse-nettle roots are micro-crystals. In calumba, stillingea, krameria, licorice, scamony root are prisms. In saponaria, jalap, althea, spikenard, rumex, rhubarb are rosette crystals. In pleurisy roots both prisms and rosettes occur.