DESCRIPTION OF PLATE VI FIG. 28.-Illustrating the Histology of a Typical Bark Showing all of the Tissues Which May be Found in a Bark.-A, Longitudinal section in the radial direction but not showing the medullary rays. B, Transverse section. 1. Outer bark. The demarkation between outer and inner bark is not always distinct. 2. Inner bark. 3. Beginning of wood tissue. a, Epidermis. Always wanting in tree trunks and older branches. b, Cork tissue. c, Bark parenchyma. Cell-walls are usually not suberized and the cells may contain various inclusions such as crystals of calcium oxalate, tannin. starch granules and resin. d, Groups of sclerenchyma cells. These, when present, normally predominate in the outer bark. e, Crystal-bearing fibers which usually accompany the bast fibers. f, Bast fibers. These, when present, normally predominate in the inner bark. The fibers may occur singly or in groups. g, Cambium. h, Wood fibers. i, Ducts. Usually of the typically porous type. k, Medullary rays. An excellent typical bark having all of the histological elements indicated in Plate VI is Rhamnus purshiana. The demarkation between outer bark and inner bark is well defined in Ulmus and Quillaja. CHAPTER VIII KEYS TO THE STUDY AND IDENTIFICATION OF SIMPLE POWDERED VEGETABLE DRUGS The two keys are supplementary to each other. Each key may, however, be used alone as it is independently complete in itself. Since the recognition of the identity of a vegetable powder is primarily dependent upon a careful microscopical examination, it is evident. that the key based on the gross characteristics is of secondary value. The use of the keys will serve two very important purposes. It compels careful macroscopical and microscopical examination of the drugs and it establishes a uniform and logical sequence in the method and manner of examination. The use of the keys as a means of identification of the drugs is largely incidental. As the student gains more and more experience in the critical study and examination of the vegetable drugs listed in the keys, the keys lose more and more in primary value and significance. I. KEY BASED UPON THE ORGANOLEPTIC TESTS. This key will prove an aid to the study and identification of powders by those who are not in possession of a compound microscope. It will be noted that the major divisions or groupings are based on color and for that reason the key is somewhat defective or confusing, because of the variation in colors, as has been explained elsewhere, and also because the powders fade quite rapidly, even if kept well in the dark. Basing the primary or major grouping on color differences is, however, wholly consistent because this character is, as a rule, striking and is the very first to be observed. It should also be borne in mind that the odors and tastes cited refer to crude drugs. The process of powdering does not change the taste and odor qualitatively, but quantitatively these properties lessen considerably with time. The following suggestions may prove useful. If the odor is very weak, it may be concluded that the powder is old, or that it may be adulterated with some odorless substance. If the taste is abnormally weak, the addition of some. tasteless substance may be suspected. In comparatively rare in |