CONDUCTING TISSUE 141 



On cross-section the medullary rays are seen to vary greatly. 

 In many plants they are more or less straight radial lines, as 

 in quassia (Plate 105, Fig. 2); while in other plants they form 

 wavy lines where they bend or curve around the conducting 

 cells, as in piper methysticum, kava-kava (Plate 48, Fig. A). 



In the study of powdered drugs the radial view of the medul- 

 lary rays is most frequently seen. 



In a perfect radial section (Plate 107, Fig. 2) the medullary 

 rays are seen as tiers of cells in contact throughout their long 

 diameter, and they run at right angles to the long diameter of 

 the other cells. This view of the rays shows the length and 

 height of the medullary ray. In logwood the rays are often 

 forty cells high. In powdered barks, woods (Plate 47), and 

 woody roots the radial view of the medullary rays is frequently 

 diagnostic. 



In guaiacum officianale wood the medullary rays are one 

 cell wide on cross-section, and up to six cells high on the tan- 

 gential section. In santalum album the rays are from one to 

 three cells wide on cross-section, and up to six cells high on 

 tangential section. In the greater number of plants the rays 

 are more than one cell wide. 



THE MEDULLARY RAY CELL 



The medullary ray cell (Plate 48, Fig. i) is one of the in- 

 dividual cells making up the medullary ray bundle and the 

 medullary ray. 



The cross-sections of the cells which are seen in tangential 

 sections show the cells to be mostly circular in outline when 

 they occur in the central portion of medullary ray bundles of 

 more than two cells in width; but they are more irregular in 

 outline when the medullary ray bundle is only one cell wide. 

 Even the cells of the three or more cell-wide bundles have ir- 

 regular, outlined cells at the ends of the bundle and on the sides 

 in contact with the other tissues. 



The length and height of the medullary ray cell are shown 

 in radial sections; while the width and length of the medullary 

 ray cells are shown in cross-sections. 



