The microscopic examination of insect powder is difficult for the reason that there are so many elements to be constantly kept in mind. The parts of the flower which contribute characteristic cells are the stem, involucre, ray flowers, disk flowers, and the receptacle. In each of these parts there are many different types of cells. There are practically two types of flowers found in insect powder of commerce: first, closed or immature flowers, and secondly, open or mature flowers. As explained above, the half-open flowers consist largely of the two above-named varieties. Let us first consider the structure of the closed insect flowers as illustrated in Plate 118. [Illustration: PLATE 118 POWDERED CLOSED INSECT FLOWER (_Chrysanthemum cinerariifolium_, [Trev.] Vis.) 1. Edge of scale. 2. Fibre of scale. 3. Hairs. 4. Upper epidermis of ray flower. 5. Under epidermis of ray flower. 6. Cross-section of ray petal. 7. Parenchyma of ray flowers with crystals. 8. Lobe of disk petal. 9. Filament tissue. 10. Calyx tissue, 11. Lobe of stamen. 12. Pollen. 13. Papillæ of stigma. 14. Secretion cavity with surrounding cells. 15. Parenchyma of the receptacle.] The involucre has many characteristic cells. The more prominent ones seen in the powder are the edge of the scale with the attached hair (Fig. 1). These hairs (Fig. 3) are T-shaped. The terminal cell is expanded laterally, and it terminates in two points. Connecting the terminal cell with the epidermis are two or three cells which are slightly longer than broad. In the powder the terminal cell is usually attached to fragments only of the supporting cells. Fibres of the bracts have thick, wavy, porous walls, and they have a tendency to occur in masses. The upper epidermis (Fig. 4) of the ray-flower petal is prominently papillate. The under epidermis consists of wavy cells without papillæ. Another view of the papillæ is shown in Fig. 6. The parenchyma of the ray flowers (Fig. 7) contain cubical crystals. The lobe of the disk-flower petal (Fig. 8) is papillate at the end, the terminal cells have thick outer and thin inner walls. The filament tissue (Fig. 9) is composed of nearly square cells. The calyx tissue (Fig. 10) is made up of thin-walled cells with slightly papillate margins. The lobe of the stamen (Fig. 11) consists of nearly uniform epidermal cells which are in contact throughout their long diameter, while the hypodermal cells are thin-walled and angled. The pollen grains (Fig. 12) are dark yellowish green, thin, and the wall does not appear perforated by pores. The papillæ of the stigma (Fig. 13) are clustered, club-shaped, and nearly white in color. They are usually found detached in the powder. All parts of the pistil contain secreting cells, but the most conspicuous secreting cavities (Fig. 14) are those of the ovary. These cavities appear brownish in color and are surrounded by small cells which appear indistinct on