130 
PHARMACEUTICAL BOTANY 
into an inner and an outer layer. The outer layer has become the 
cork cambium, cutting off cork on its outer face beneath the endo- 
dermis. Cork being an impermeable barrier to water has prevented 
the nourishing sap from percolating through to the endodermis, cor¬ 
tex and epidermis. These regions have consequently begun to sluff 
off. Note that the cambium has begun to spread out into the form 
Fig. 63.—Transverse section of California Privet root made about an inch and 
a half above the section shown in Fig. 61 and showing secondary structure. 
Note that epidermis, primary cortex and endodermis have completely disappeared. 
Cork ( ck)\ phellogen ( ph ); secondary cortex (sc); protophloem (p')] secondary 
phloem ( p 2 ); cambium (c); secondary xylem ( x 2 ) and protoxylem ( x'). 
(Photomicrograph). 
of a ring. More secondary xylem has been formed on its inner face 
and additional secondary phloem has appeared on its outer face. 
(Fig. 62.) , 
D. Make a permanent mount of a fourth T. S. cut through the 
same root some distance above the third. Note that the epidermis, 
primary cortex and endodermis have completely peeled off. Cork 
is found as the external bounding layer and underneath it, cork 
