MICROSCOPICAL EXAMINATION OF POWDERED VEGETABLE DRUGS 81 



oped in willow bark, in cotton root bark, mezereum, etc. Widely 

 distributed in barks, stems and roots. 



Sclerenchymatous : Short cells with greatly thickened and usually 

 porous, lignified walls. Typically developed in cinchona barks, 

 cinnamon barks, sassafras bark, etc. 



Branching : Cells usually elongated and more or less branching at 

 the ends, as in wild cherry bark, soap bark, etc. Not very com- 

 mon. 



SCLERENCHYMA CELLS OR STONE CELLS. Cells generally not greatly 

 elongated; thickened, porous and lignified walls; often of brownish 

 color; ends not tapering pointed. 



Typical: Cells approximately isodiametric ; walls may be greatly 

 thickened, comparatively thin-walled or unevenly thickened. 

 Very widely distributed in the plant kingdom; found in barks 

 (especially the outer bark), roots, fruits (principally in the peri- 

 carp), in the pear, quince, etc. 



Elongated or Bast -Like: Resemble short bast cells but ends are 

 truncate instead of tapering pointed. Found in some barks (coto) , 

 in star anise, some roots, coffee hulls, currants, etc. 

 Branching: Never greatly elongated. Typically developed in tea 

 leaves, in some nut shells (peanut pericarp), seed pits (endocarp), 

 some barks, etc. 



WOOD FIBERS OR WOOD CELLS. Differ from bast in that the fibers are 

 more firmly bound together, more porous, always lignified, much 

 more uniform in transverse diameter though walls vary consid- 

 erably in thickness. Ends usually very blunt, or truncate, or 

 diagonally cut. 



TRACHEIDS. Resemble wood fibers very closely, cell-walls more porous 

 as a rule, ends tapering pointed, walls usually lignified. Typical 

 bast, wood fibers and tracheids are similar as to the measure- 

 ments of the transverse diameter. The following are the principal 

 kinds. 

 Typical: Walls always lignified, very porous, forming the woody 



tissue. 

 Tracheids with Bordered Pits : Typically developed in the pines, 



forming the woody structure. Rare in other plant groups. 

 Bast-Like Tracheids : Soft, flexible, generally non-lignified elements; 

 ends tapering pointed. Not a diagnostic tissue in any of the 

 important drug plants. In roots, some young barks, etc. 

 DUCT OR VESSELS. The water conducting tubes o& vascular bundles 

 and of other conducting tissues. Always lignified. The following 

 are the principal types : 



