124 PHARMACEUTICAL BOTANY 



asjiosts, 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: 



i. 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 fibro-vascular bundle of many alternating xylem and 

 phloem patches and hence poly arch. 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. 



