Papillæ occur on the following parts of the plant: flower-petals, stigmas, styles, leaves, stems, seeds, and fruits. Papillæ occur on only a few of the medicinal leaves. The under surface of both Truxillo (Plate 6, Fig. 3) and Huanuca coca have very small papillæ. The outermost wall of these papillæ are much thicker than the side walls. The papillæ of klip buchu (Plate 6, Fig. 4), an adulterant of true buchu, has large thick-walled papillæ. The velvety appearance of most flower-petals (Plate 6, Figs. 2 and 5) is due to the presence of papillæ. The papillæ of flower-petals are very variable. In calendula flowers (Plate 6, Fig. 1) they are small, yellowish in color, and the outer wall is marked with parallel striations which appear as small teeth in cross-section. The ray petal papillæ of anthemis consist of rather large, broad, blunt papillæ with slightly striated walls. The papillæ of the ray petals of the white daisy consist of papillæ which have medium sized, cone-shaped papillæ with finely striated walls. The papillæ of the flower stigma vary greatly in different flowers. In some cases two or more types of papillæ occur, but even in these cases the papillæ are characteristic of the species. The papillæ differ greatly in the case of the flowers of the compositæ, where two types of flowers are normally present--namely, the ray flowers and the disk flowers. In all cases observed the papillæ of the stigma of the ray flowers are always smaller than the papillæ of the stigma of the disk flowers. It would appear from extended observation that the papillæ of the ray flower stigma are being gradually aborted. The papillæ of the style are always different from the papillæ of the stigma. The style papillæ are always smaller, and they are of a different form. [Illustration: PLATE 6 PAPILLÆ 1. Calendula flowers (_Calendula officinalis_, L.). 2. White daisy ray flower (_Chrysanthemum leucanthemum_, L.). 3. Coca leaf (_Erythroxylon coca_, Lamarck). 4. Klip buchu. 5. Anthemis ray petal (_Anthemis nobilis_, L.).] UNICELLULAR NON-GLANDULAR HAIRS =True plant hairs= are tubular outgrowths of the epidermal cell, the length of these outgrowths being several times the width of the hair. The unicellular hairs are common to many plants. The two groups of non-glandular unicellular hairs are, first, the solitary; and secondly, the clustered hairs. =Solitary unicellular hairs= occur on the leaves of chestnut, yerba santa, lobelia, cannabis indica, the fruit of anise, and the stem of allspice, senna, and cowage. Chestnut hairs (Plate 7, Fig. 1) have smooth yellowish-colored walls, and the cell cavity contains reddish-brown tannin. These hairs occur solitary or clustered; the clustered hairs normally occur on the leaf, but in powdering the drug, individual hairs of the cluster become separated or solitary.