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PHARMACEUTICAL BOTANY 
1. Epidermis with cutinized outer walls, the cells often elongating 
to form root-hairs. 
2. Hypodermis. 
3. Primary cortex with usually small intercellular spaces. 
4. Endodermis, or innermost layer of cells of the cortex with 
lenticularly thickened radial walls. 
5. Pericambium of one to two layers of actively growing cells 
which may produce side rootlets. 
6. Radial fibro-vascular bundle of four, rarely two or three or five 
or six phloem patches alternating with as many xylem arms. Not 
uncommon to find bast or phloem fiber along outer face of each 
phloem patch. Xylem has spiral tracheae, internal to these a few 
pitted vessels, then, as root ages, more pitted vessels, also xylem 
cells and wood fibers make their appearance. 
B. Of Secondary Growth (Most official roots). 
At about six weeks one notes cells dividing by tangential walls in 
the inner curve of phloem patches. This is intrafascicular cambium. 
A single layer of flattened cells starts to cut off on its inner side a 
quantity of secondary xylem and pushes out the patches of bast 
fibers, adds a little secondary phloem on the outer side. Secondary 
xylem finally fills up the patches between the arms. The patches of 
bast fibers get flattened out. The pericambium has a tendency to 
start division into an inner and outer layer. The outer layer be- 
comes a cork cambium (phellogen) surrounding the bundle inside of 
the endodermis. It cuts off cork tissue on its outer face, hence all 
liquid material is prevented from filtering through and cortex includ- 
ing endodermis, as well as the epidermis, shrivel and dry up and 
separate off at the age of two to three months. The cork cambium 
(phellogen) may lay down secondary cortex internal to itself and 
external to the phloem. 
Patches of cells of the inner layer of pericambium divide rapidly 
and are called interfascicular cambium. These join the intrafasci- 
cular cambium to form a continuous cambium ring which then 
cuts off additional secondary xylem on its inner face and sec- 
ondary phloem on its outer face pushing inward the first-formed 
or protoxylem and outward the first-formed or protophloem. The 
medullary rays become deepened. 
