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 (i) 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. 



