152 



PHARMACEUTICAL BOTANY 



tain living cells, functioning in the vegetative processes of the plant, 

 constitute ,the alburnum or sap-wood. The drug Quassia is a good 

 example of this kind of wood. The inner dead colored layers con- 

 stitute the duramen or heart-wood. Important examples of this 

 kind of wood used in pharmacy are Lignum Guaiaci, Haematoxylum, 

 and Santalum Album. 



Microscopic Characteristics of Angiospermous and Gymnosperm- 

 ous Woods. The wood of Angiosperms is characterized by the pres- 

 ence of tracheae (vessels) with various markings on their walls, 



particularly by small pits in the walls 

 ot some of the tracheae, together with 

 wood fibers, wood parenchyma and 

 medullary rays. 



The wood of Gymnosperms is made 

 up for the larger part ot tracheids with 

 bordered pits which latter are charac- 

 terized in radial longitudinal section by 

 the presence of two rings, one within 

 the other. A single row of these is 

 seen on the tracheid wall. Medullary 

 rays, frequently diagnostic for different 

 species and woody parenchyme cells, 

 are also found. 



Histology of Typical Herbaceous 

 Monocotyl Stems (Endogenous). Passing from exterior toward 

 center the following structures are seen: 



1. Epidermis whose cells are cutinized in their outer walls. 



2. Hypodermis, generally collenchymatic. 



3. Cortex. 



4. Endodermis or innermost layer of cortex. 



5. A large central zone of parenchyma matrix in which are found 

 scattered nbro-vascular bundles of the closed collateral or rarely 

 concentric type (amphi vasal) . In this latter type, which is typical 

 of old monocotyl stems, the xylem grows completely around phloem 

 so that phloem is found in the center and xylem without and sur- 

 rounding it. 



FIG. 78. Photomicrograph 

 of cross-section of very young 

 cornstalk, where certain pler- 

 ome strands have just gone 

 over into vascular bundles. 

 For comparison with Fig. 79. 

 (Stevens.) 



