=Under Epidermis.= The under epidermal cells are modified to form papillæ which are similar to the papillæ of the upper epidermis. =Fibro-Vascular Bundle.= The cells composing the vascular bundle are sieve cells, vessels, and fibres. The =sieve cells= are small and the walls are white and angled. The =vessels= have thick, white, angled walls. The =bast fibres= are rounded in outline and the walls are thick and white. =Endodermis.= The endodermal cells encircle the fibro-vascular bundles. The cells are large, thin-walled, and oval in shape. =Secretion Cells.= Near the edges of the leaf are schizogenous secretion cavities surrounded by thin-walled secretion cells. POWDERED KLIP BUCHU When the leaf is powdered (Plate 109), the cells are quite as characteristic in appearance. The upper epidermal cells (1) have thick-beaded, yellowish-white walls and papillate outer walls. No stomata occur on the upper surface. The under epidermis (2) with numerous stomata, is surrounded by the characteristic guard cells. The end walls are beaded as on the upper surface. The palisade cells (3) appear as in the cross-section. The conducting cells (4 and 4) are of the spiral and pitted type. The papillæ (5 and 5) are very abundant in the powder and very characteristic. The fragments of the epidermis (6) are also abundant. The mesophyll (7) is characteristic, as it retains its form when powdered. The fibres (8) are usually associated with the conducting cells; occasionally they are found free as in the illustration. [Illustration: PLATE 109 POWDERED KLIP BUCHU 1. Upper epidermis. 2. Under epidermis. 3. Palisade cells with chlorophyll. 4 and 4. Conducting cells. 5 and 5. Papillæ. 6. Fragments of the epidermis. 7. Mesophyll. 8. Fibres.] MOUNTAIN LAUREL =Epidermis.= The epidermal cells of mountain laurel are occasionally modified, as unicellular hairs (Plate 110, Fig. 1), particularly in the region of the veins. The ordinary epidermal cells have thick outer walls and thin inner walls. Beneath many of the epidermal cells are large air-spaces. =Upper Palisade Parenchyma.= The palisade parenchyma vary from four to five layers. The inner palisade cells are shorter and broader than the outer layer of cells. =Parenchyma.= The parenchyma cells (Fig. 4) are rounded in form and they are arranged in the form of columns which are one cell in thickness above, but two to three cells in thickness near the under epidermis. Between each chain of cells is a larger intercellular space (Fig. 6). In a few of the cells are large rosette crystals. =Under Epidermis.= The under epidermal cells are uniformly smaller than the upper epidermal cells. It is thus seen that mountain laurel leaf has no hypodermal cells; no spongy parenchyma; no under palisade cells; no under hypodermal cells, and no secretion cavities. TRAILING ARBUTUS