250 HISTOLOGY OF MEDICINAL PLANTS 
The medullary rays form wavy lines. The medullary ray 
cells are radially elongated, rectangular in shape, and they con- 
tain granular cell contents. The sieve cells are either square 
or rectangular in shape. The walls are thin and white. The 
storage cavities are either filled with starch or with prisms 
and tannin. 
POWDERED WHITE PINE BARK 
White pine bark (Plate 104) when powdered shows the 
following characteristic elements: 
The microscopic structure of a powdered white pine is as 
follows: The epidermis (1) consists of reddish-brown masses, 
irregular in outline. The outer parenchyma cells are of a bright- 
green color, owing to the presence of chlorophyll. (The above 
elements are not usually found in the rossed bark.) The paren- 
chyma (3) with starch usually occurs in longitudinal sections 
accompanied with sieve cells. Often the tissue separates trans- 
versely, showing the medullary rays (4) with their granular cell 
contents (9) and the inner parenchyma cells filled with starch 
and the surrounding sieve cells. 
The crystals are nearly perfect cubes and occur singly (5) 
or in groups (6). On the longitudinal section of the bark the 
crystals occur in parenchyma cells surrounded by a reddish cell 
content and form parallel rows which are very characteristic. 
The resin occurs either as white, angled fragments (7) in a water 
mount, or as globular mass (8) or as reddish-brown pieces (10). 
The starch is very abundant and is distributed through the 
field. The diagnostic grain is lens-shaped, with a cleft hilum, 
which is nearly straight, or slightly curved, and runs parallel 
to the long diameter of the grain. The addition of ferric 
chlorid T. S. will show the presence of tannin by forming a 
dark coloration. The identification of the starch is facilitated 
by the addition of a weak Lugol’s solution, which imparts a 
blue coloration to the starch grain. 
The form, amount, and distribution of the cells composing 
the bark differ greatly in different plants. 
In cramp bark the cork and phellogen cells are very large, 
while in cascara sagrada the phellogen and the cork cells are 
very small. 
