MICROSCOPICAL EXAMINATION OF POWDERED VEGETABLE DRUGS 89 



the cells are quite free of stored food substances or formed organic 

 contents as starch, proteid granules, etc. They may contain resin. 

 Resin glands are common in the pericarp of many fruits, as in the 

 umbelliferse. The cells are generally quite large, thin-walled porous 

 and loosely united. The parenchyma cells of fleshy fruits especially 

 are very thin-walled and filled with cell-sap. 



4. BARKS 



The medicinal barks present many striking and diagnostic his- 

 tological characteristics, principally due to the relationship and 

 variation in the two predominating tissues associated with the cork 

 tissue (outer bark) and bark parenchyma, namely, bast and scleren- 

 chyma. There are also some striking cell-contents. The predominat- 

 ing color of the powdered bark is reddish-brown. Some are very 

 light, as Ulmus and Quillaja. A few are very dark, as Juglans. 



There is no reliable means of distinguishing between root barks 

 and stem barks, either macroscopically or microscopically, especially 

 when the outer bark has been removed, as is often the case. As a 

 rule root barks contain considerable starch and the color of powders 

 made therefrom is grayish in tone. Lichen elements and hyphal tis- 

 sue of higher fungi are wanting. 



1. Outer Bark Parenchyma. This tissue usually consists of typical 

 cork cells and it displaces the epidermis. The cells may be diagnostic 

 in form and size. They may contain proteid granules, tannin granules 

 and reddish-brown coloring matter. Also crystals of calcium oxalate 

 (aggregate and prismatic). This tissue is removed in peeled barks, as 

 Ulmus, Quillaja, cinnamons and others. 



2. Lenticels. These never present diagnostic characters in powders. 

 The cells are suberized and usually empty. 



3. Inner Bark Parenchyma. This differs from the outer par- 

 enchyma, in that the cells are less typically suberized and are more 

 characteristic as to form and contents. The cells are usually loosely 

 united, oval to somewhat elongated; walls colorless and of some 

 thickness. Note cell-contents carefully. Starch, which is present in 

 variable quantity, is rarely diagnostic. Crystals (mostly calcium 

 oxalate) are quite important. The acicular, prismatic and aggregate 

 forms predominate. Minute crystals (crypto-crystalline) occur in 

 cinchona and cinnamons. Resinous and waxy contents may prove of 

 diagnostic value, also coloring matter, mucilage, etc. Occasionally the 

 outer cell layers of this tissue become more or less collenchymatous. 



4. Ducts and Glands. These are generally of no great diagnostic 

 value in powders. The contents are of some diagnostic value. 



