Yerba santa hairs (Plate 7, Fig. 4) are twisted, the lumen or cell cavity is very small, and the walls, which are very thick, are grayish-white. Lobelia hairs (Plate 7, Fig. 5) are very large. The walls are grayish-white, and the outer surface extends in the form of small elevations which make the hair very rough. The hair tapers gradually to a solid point. Cannabis indica hairs (Plate 7, Fig. 6) are curved. The apex tapers to a point and the base is broad, and it frequently contains deposits of calcium carbonate. The walls are grayish-white in appearance, and rough. The roughness increases toward the apex. The hairs of anise (Plate 7, Fig. 7) are mostly curved; the walls are thick, yellowish-white, and the outer surface is rough; this is due to the numerous slight centrifugal projections of the outer wall. Allspice stem hairs (Plate 7, Fig. 2) have smooth walls. The cell cavity is reddish-brown. The hair is curved. The hair of senna (Plate 7, Fig. 10) is light greenish-yellow with rough papillose walls. The hair is usually curved and tapering, and it does not have any characteristic cell contents. [Illustration: PLATE 7 UNICELLULAR SOLITARY HAIRS 1. Chestnut leaf (_Castanea dentata_, [Marsh] Borkh). 2. Allspice stems (_Pimento, officinalis_, Lindl.). 3. Cowage. 4. Yerba santa (_Eriodictyon californicum_, [H. and A.] Greene). 5. Lobelia (_Lobelia inflata_, L.). 6. Cannabis indica (_Cannabis saliva_, L.). 7. Anise fruit (_Pimpinella anisum_, L.). 8. Hesperis matronalis (_Hesperis matronalis_, L.). 9. Galphimia glauca (_Galphimia glauca_, Cav.). 10. Senna (_Cassia angustifolia_, Vahl.).] [Illustration: PLATE 8 CLUSTERED UNICELLULAR HAIRS 1. and 2. European oak (_Quercus infectoria_, Olivier). 3. Kamala (_Mallotus philippinensis_, [Lam.] [Muell.] Arg.). 4. Witch-hazel leaf (_Hamamelis virginiana_, L.). 5. Althea leaf (_Althæa officinalis_, L.).] Cowage hairs (Plate 7, Fig. 3) are lance-shaped, and they terminate in a sharp point. The outer wall contains numerous recurved teeth-like projections. The cell cavity is filled with a reddish-brown contents which are somewhat fissured. =Clustered unicellular hairs= occur on the leaves of chestnut, witch-hazel, althea, European oak, etc. In European oak (Plate 8, Figs. 1 and 2) clusters of two and three hairs occur. The walls are yellowish-white, smooth, and the tip of the hair is solid. In kamala (Plate 8, Fig. 3) clusters of seven or more hairs occur; the walls are yellowish, and the cell cavity is reddish-brown. In witch-hazel leaf (Plate 8, Fig. 4) clusters of a variable number of hairs occur. The hairs, which are of various lengths, have yellowish-white, thick, smooth walls, and reddish cell contents. In althea leaf (Plate 8, Fig. 5) the hairs are nearly straight and the walls are smooth. The basal portions of the hair are strongly pitted.