1. Capsicum seed (_Capsicum frutescens_, L.). 2. Lobelia seed (_Lobelia inflata_, L.). 3. Henbane seed (_Hyoscyamus niger_, L.).] [Illustration: PLATE 5 TESTA CELLS 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. PLANT HAIRS (TRICHOMES) 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. In systematic work, as in pharmacognosy, we must work with dried material, and it is only those hairs which retain their form under such conditions which are of classification value. Hairs are the most common outgrowths of the epidermal cells. They are classified as glandular or non-glandular, according to their structure and function. The glandular hairs will be considered under synthetic tissue. Each group is again subdivided into a number of secondary groups, depending upon the number of cells present, their form, their arrangement, their size, their color, the character of their walls, whether rough or smooth, whether branched or non-branched, whether curved, twisted, straight, or twisted and straight, whether pointed, blunt, or forked. FORMS OF HAIRS PAPILLÆ =Papillæ= are epidermal cells which are extended outward in the form of small tubular outgrowths.