210 PHARMACEUTICAL BOTANY 
prisms of calcium oxalate occur in parenchyma cells of this 
region. 
4. PHLoeM, or inner bark, a very broad zone composed of 
irregular-shaped, elongated phloem masses separated from each 
other by medullary-rays which converge in the outer phloem 
region. Each phloem mass consists of numerous sieve tubes, 
rcr 
a) 2 $i 
mp 
fi 
Fic. 140.—Cascara Sagrada Bark. Tangential-longitudinal section through 
outer phloem region. , phloem parenchyma; sf, group of stone cells; rcr, rosette 
aggregates of calcium oxalate; mr, medullary ray; si, sieve tubes; crf, crystal fibers 
containing monoclinic prisms of calcium oxalate; mp, monoclinic prism. 
companion cells and phloem cells, some of which latter contain 
spheroidal starch grains while others contain either monoclinic 
prisms or rosette aggregates of calcium oxalate. Embedded 
within the phloem masses, in tier-like fashion, will be noted 
groups of bast or phloem fibers, each group of which is sur- 
rounded by a row of crystal fibers, individual cells of which can 
only be made out in this kind of a section. Each of these con- 
tains a monoclinic prism of calcium oxalate. The medullary- 
