Hypodermal cells are very likely to occur on the margin of the leaf. Uva-ursi leaf has a structure typical of leaves with hypodermal marginal cells. Uva-ursi, like other leaves with hypodermal cells has a greater number of hypodermal cells at the leaf margin than at any other part of the leaf surface.
The cutinized walls of epidermal cells are stained red with saffranin.
=Testa epidermal cells= form the epidermal layers of such seeds as lobelia, henbane, capsicum, paprika, larkspur, belladonna, scopola, etc.
In surface view the end walls are thick and wavy in outline; frequently the line of union--middle lamella--of two cells is indicated by a dark or light line, while in others the wall between two cells appears as a single wall. The walls are porous or non-porous, and the color of the wall varies from yellow to brown, to colorless. These cells always occur in masses, composed partially of entire and partially of broken fragments.
In lobelia seed (Plate 4, Fig. 2) the line of union of adjacent cell walls appears as a dark line. The walls are wavy in outline, of a yellowish-red color and not porous.
In henbane seed (Plate 4, Fig. 3) the line of union between the cells is scarcely visible; the walls are decidedly wavy, more so than in lobelia, and no pits are visible.
In capsicum seed (Plate 4, Fig. 1) the cells are very wavy and decidedly porous, the line of union between the cell walls being marked with irregular spaces and lines.
In belladonna seed (Plate 5, Fig. 1) the walls between two adjacent cells are non-striated and non-porous, and extremely irregular in outline.
1. Capsicum seed (_Capsicum frutescens_, L.). 2. Lobelia seed (_Lobelia inflata_, L.). 3. Henbane seed (_Hyoscyamus niger_, L.).]
1. Belladonna seed (_Atropa belladonna_, L.). 2. Star-aniseed (_Illicium verum_, Hooker). 3. Stramonium seed (_Datura stramonium_, L.).]
In star-anise seed (Plate 5, Fig. 2) the walls are irregularly thickened and wavy in outline.
In stramonium seed (Plate 5, Fig. 3) the walls are very thick, wavy in outline, and striated.
In histological work plant hairs are of great importance, as they offer a ready means of distinguishing and differentiating between plants, or parts of plants, when they occur in a broken or finely powdered condition. There is no other element in powdered drugs which is of so great a diagnostic value as the plant hair. The same plant will always have the same type of hair, the only noticeable variation being in the size. In microscopical drug analysis the presence of hairs is always noted, and in many cases the purity of the powder can be ascertained from the hairs. Botanists seem to have given little attention to the study of plant hairs. This accounts for the fact that information concerning them is very meagre in botanical literature, and, as far as the author can learn, no one has attempted to classify them. In systematic work, plant hairs could be used to great advantage in separating genera and even species. Hairs are, of course, a factor now in systematic work. The lack of hairs is indicated by the term glabrous. Their presence is indicated by such terms as hispid, villous, etc. In certain cases the term indicates position of the hair as ciliate when the hair is marginal. When hairs influence the color of the leaf, such terms as cinerous and canescent are used. In all the cases cited no mention is made of the real nature of the hair.