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 cmnamon 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. 
