92 
PHARMACEUTICAL BOTANY 
6. Radial fibro-vascular bundle of five xylem arms alternating 
with as many phloem patches. Note the narrow spiral tracheae in 
the xylem patches. 
The section you have just studied illustrated in general the appear- 
ance of any Dicotyl root of primary growth. 
B. Mount permanently another T. S. cut through the same root a 
short distance above the first. 
Note that this is somewhat larger in diameter. Observe the root 
hairs starting from the epidermis; a broad cortex; a large clear and 
open looking endodermis; then pericambium; next, a central patch 
of xylem showing a faint pentarch relation. Pushed out are five 
phloem tracts. Each of these constitutes a mass of protophloem 
(first formed phloem). On the inner face of each phloem mass may 
be seen intrafascicular cambium. At the outer end of each xylem 
tract there has been cut off a patch of fine cambial cells (interfascic- 
ular cambium) which becomes joined to the intrafascicular cambium 
to develop secondary phloem on the outer face and secondary xylem 
on the inner face. 
C. Mount permanently a third T. S. out through the same root a 
short distance above the second. Note that this is still larger in 
diameter than the second. The pericambium has already divided 
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. The epidermis has consequently begun to sluff 
off. Note that the cambium has begun to spread out into the form 
of a ring. More secondary xylem has been formed on its inner face 
and additional secondary phloem has appeared on its outer face. 
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 
cambium. This cork cambium has developed secondary cortex on 
its inner face. The cambium has assumed a circular aspect. Just 
beneath the secondary cortex will be found flattened patches of 
protopliloem, and beneath these secondary phloem masses have 
