The =phloem parenchyma= cells resemble the sieve cells, but they are larger. The =bast fibres= occur singly or in groups of two or three. The walls are white, non-porous, and non-striated. =Cambium.= The cambium layer is composed of rectangularly shaped cells, which are frequently obliterated. =Xylem.= The xylem contains vessels, wood parenchyma, and medullary rays. The =vessels= are large, rounded cells with thick walls. The wood parenchyma consists of thick-walled cells of irregular size and form. The =medullary rays= are tangentially elongated and rectangular in form. =Pith parenchyma.= The pith parenchyma cells are rounded in outline and as large as the cortical parenchyma cells. POWDERED PINK ROOT When the roots and rhizomes of spigelia are powdered (Plate 93) they show the following structure: The epidermal cells are small and brownish on surface view, varying in size from 13 by 18 micromillimeters to 31 by 40 micromillimeters. When associated with parenchyma they appear as black masses. The cortical parenchyma cells are rounded and vary in size from 23 by 26 micromillimeters to 37.5 by 90 micromillimeters. Many of the cells from the root contain larger quantities of minute single rounded starch grains varying in size from 1 micromillimeter to 4 micromillimeters. The larger round single starch grains are found in both the cortical and pith parenchyma of the rhizome. They vary in size from 5 micromillimeters to 18 micromillimeters. The conducting elements are pitted tracheids varying from 10 micromillimeters to 38 micromillimeters in diameter. A few pitted and annular vessels are also found. The only fibres occurring are found in the xylem. They are not a prominent feature of the powder, as their walls break up into minute fragments. The pith parenchyma varies in size from 13 by 19 micromillimeters to 75 by 82.5 micromillimeters. It is in these cells that the largest starch grains occur. Distinguishing diagnostic characters of the powder: 1. Parenchyma with starch. 2. Dark masses of epidermal tissue. 3. Spigelia should contain starch, and it should not contain cystoliths, stone cells, or long, white-walled bast fibres. POWDERED RUELLIA ROOT When the roots of ruellia root and rhizome are powdered (Plate 94) they show the following structure: [Illustration: PLATE 93 POWDERED SPIGELIA MARYLANDICA, L. 1. Epidermis and cortical parenchyma. 2. Tracheids and fibres. 3. Parenchyma cells of the root containing the small starch grains, longitudinal view. 4. Parenchyma of the rhizome containing the large starch grams, transverse view. 5. Tracheids. 6. Surface view of the epidermal cells. 7. Starch scattered through the field. 8 and 8´. Dark masses of epidermal and underlying tissue.] [Illustration: PLATE 94 POWDERED RUELLIA CILIOSA, Pursh.