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PHARMACEUTICAL BOTANY 
as hosts, and absorb nutritious juices from them. The Mistletoe , 
Dodder and Geradia are typical parasites. 
Duration of Root. -Plants are classified according to the duration 
of the root, as follows: 
1. Annual plants are herbs with roots containing no nourishment 
for future use. They complete their growth, producing flower, 
fruit and seed in a single season, then die. 
2. Biennial plants develop but one set of aerial organs the first 
year, e.g., the leaves, and, as in the beet and turnip, etc., a large 
amount of reserve food material is stored in the root for the support 
of the plant the'following season when it flowers, fruits and dies. 
3. Perennial plants live indefinitely, as trees. 
Root Histology.—Monocotyledons.—The histology of mono- 
cotyledonous roots varies, depending upon relations to their sur¬ 
roundings, which may be aquatic, semi-aquatic, mesophytic, or 
xerophytic. In this connection we will discuss only the type of 
greatest pharmacognic importance, i.e., the mesophytic type as 
seen in its most typical form in the transverse section of Honduras 
Sarsaparilla root. 
Examining such a section from periphery toward the center, one 
notes the following: 
1. Epidermis of a single layer of cells many of which give rise to 
root-hairs. 
2. Hypodermis of two or three layers of cells whose walls are 
extremely thickened. 
3. Cortex, consisting of a broad zone of parenchyma cells many 
of which contain starch grains. 
4. Endodermis of one layer of endodermal cells whose walls are 
extremely thickened through the infiltration of suberin and lignin. 
5. Pericambium of one or two layers of meristematic cells whose 
walls are extremely thin. 
6. A radial Jibro-vascular bundle of many alternating xylem and 
phloem patches and hence polyarch. The phloem tissue consists 
of phloem cells and sieve tubes. The xylem is composed of xylem 
cells, tracheae and wood fibers. 
7. Medulla or pith composed of parenchyma cells containing starch 
and often showing xylem patches cut off and enclosed within it. 
