174 PHARMACEUTICAL BOTANY 
D. MA@ke a permanent mount of a fourth cross section cut 
through the same root some distance above the third. Note that 
the epiderr#s, brimary cortex and endodermis have completely peeled 
off. Cork is found as the external bounding layer and underneath 
it, cork cambium. This cork cambium has developed secondary 
on gemma neem RS — — 
ccc 
Fic. 106.—Photomicrograph of a transverse section of an older portion of Cali- 
fornia Privet *0ot, showing further secondary development. XX 35. Note the 
prominent medullary rays (mr); cork (ck); phellogen (ph); secondary cortex 
(between ph and ’); protophloem (p’); secondary phloem (2); cambium (c); 
secondary xylem (x?), the leader pointing to a trachea; wood fibers between 
trachez; and Pprotoxylem (x’). 
cortex on its inner face. The cambium has assumed a circular 
aspect. Just beneath the secondary cortex will be found flat- 
tened patches of protophloem, and beneath these secondary phloem 
masses have been formed through the activity of the cambium. 
The cambium has developed new or secondary xylem on its inner 
face which has pushed the first formed or protoxylem toward the 
center of the root. The pith has disappeared and its place is 
taken by protoxylem (Figs. 105 and 106). 
