172 HISTOLOGY OF MEDICINAL PLANTS 



In calamus (Plate 62, Fig. A) the cavity is larger than the 

 surrounding cells; it is rounded in outline, and it contains 

 oleoresin. These cavities are in contact with the ordinary 

 parenchyma cells, from which they are easily distinguished by 

 their larger size and rounded form. 



The unicellular oil cavity of canella alba (Plate 63, Fig. A) 

 is rounded or oval in cross-section and is many times larger 

 than the surrounding cells. The wall, which is very thick, is 

 of a yellowish color. 



Secretion cavities vary greatly in form, according to the 

 part of the plant in which they are found. In flower petals and 

 leaves they are spherical; in barks they are usually elliptical; 

 in umbelliferous fruits they are elongated and tube-like. 



Mucilage cavities are not of common occurrence in medicinal 

 plants. They occur, however, in the stem and root bark of 

 sassafras, the stem bark of slippery elm, the root of althea, etc. 



