MECHANICAL TISSUES 103 



The pores, which are absent in many drugs, are, when 

 present, either simple, as in echinacea root (Plate 24, Fig. 4), 

 or they are branched, as in yellow cinchona (Plate 23, Fig. 3). 



In each of the above fibres the length and width of the 

 fibre are shown. The fibres also have pores of variable length. 

 Such a variation is common to most fibres with pores. That 

 part of the wall immediately over or below the cell cavity shows 

 the end view or diameter of the pore, as in the fibre of marsh- 

 mallow root (Plate 24, Fig. 3). As a rule, however, the pores 

 show indistinctly on the upper and lower wall. 



OCCURRENCE IN POWDERED DRUGS 



In powdered drugs bast fibres occur singly or in groups. 

 The individual fibres may be broken, as in mezereum and elm 

 bark, or they may be entire, as in Ceylon cinnamon and in 

 sassafras bark (Plate 26, Figs. 2 and 3). 



The lignified walls of bast fibres are colored red by a solution 

 of phlorogucin and hydrochloric acid, and the walls are stained 

 yellow by aniline chloride. 



In fact, few of the fibres found in individual plants occur 

 in a broken condition. 



Isolated bast fibres are circular in outline. Bast fibres, when 

 forming part of a bundle, have angled outlines when they are 

 completely surrounded by other bast fibres; but when they 

 occur on the outer part of the bundle, and when in contact with 

 parenchyma or other cortical cells, they are partly angled and 

 partly undulated in outline. 



In the bast fibres the pores are placed at right angles to 

 the length of the fibre. The side walls show the length of the 

 pore (Plate 24, Fig. 3) ; while the upper or lower wall shows the 

 outline, which is circular, and the pore, which is very minute. 



Most bast fibres have no cell contents. In some cases, 

 however, starch occurs, as in the bast fibres of rubus. 



The color of the bast fibres varies, being colorless, as in 

 Ceylon cinnamon; or yellowish- white, as in echinacea; or bright 

 yellow, as in bayberry bark. 



Bast fibres retain their living-cell contents until fully de- 

 veloped; then they die and function largely in a mechanical 

 way. 



