152 
PHARMACEUTICAL BOTANY 
tain living cells, functioning in the vegetative processes of the planj, 
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 
of some of the tracheae, together with 
wood fibers, wood parenchyma and 
medullary rays. 
The wood of Gymnosperms is made 
up for the larger part of 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 fibro-vascular bundles of the closed collateral or rarely 
concentric type (amphivasal). 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.) 
