ROOTS AND RHIZOMES 227 



The wood parenchyma consists of thick- walled cells of irreg- 

 ular size and form. 



The medullary rays are tangentially elongated and rectangular 

 in form. 



Pith parenchyma. The pith parenchyma cells are rounded 

 in outline and as large as the cortical parenchyma cells. 



POWDERED PINK ROOT 



When the roots and rhizomes of spigeHa are powdered (Plate 

 93) they show the following structure: 



The epidermal cells are small and brownish on surface view, 

 varying in size from 13 by 18 micromillimeters to 31 by 40 

 micromillimeters. When associated with parenchyma they ap- 

 pear as black masses. The cortical parenchyma cells are rounded 

 and vary in size from 23 by 26 micromillimeters to 37.5 by 90 

 micromillimeters. Many of the cells from the root contain 

 larger quantities of minute single rounded starch grains varying 

 in size from i micromillimeter to 4 micromilHmeters. The 

 larger round single starch grains are found in both the cortical 

 and pith parench^Tna of the rhizome. They vary in size from 

 5 micromillimeters to 18 micromillimeters. The conducting 

 elements are pitted tracheids varying from 10 micromillimeters 

 to 38 micromillimeters in diameter. A few pitted and annular 

 vessels are also found. The only fibres occurring are found in 

 the xylem. They are not a prominent feature of the powder, 

 as their walls break up into minute fragments. The pith 

 parench}TTia varies in size from 13 by 19 micromilHmeters to 

 75 by 82.5 micromillimeters. It is in these cells that the largest 

 starch grains occur. 



Distinguishing diagnostic characters of the powder: 



1. Parenchyma with starch. 



2. Dark masses of epidermal tissue. 



3. Spigelia should contain starch, and it should not contain 

 cystoHths, stone cells, or long, white-walled bast fibres. 



POWDERED RUELLIA ROOT 



When the roots of ruellia root and rhizome are powdered 

 (Plate 94) they show the following structure: 



The epidermal cells vary from 7.8 by 15.6 micromillimeters 



