i88 BOTANY AND PHARMACOGNOSY. 



Stone cells are usually polygonal, or more or less irregular in 

 outline, sometimes even branching (Figs. 301 and 302). The 

 walls are distinctly lamellated, and they give the characteristic 

 reaction for lignocellulose with phloroglucin or aniline sulphate; 

 occasionally, however, one or more of the walls remain unthick- 

 ened. The pores are elliptical or circular on surface view. 



Bast fibers are sclerenchymatous fibers occurring in tl^e 

 bark and are usually associated with sieve cells. They may, or 

 may not, give a pronounced reaction for lignocellulose with phlo- 

 roglucin or aniline sulphate. In transverse section they are more 

 or less round or polygonal, depending upon whether they are iso- 

 lated or in groups. They vary in diameter and length, and also 

 in the thickness of the walls (Figs. 104, 299, 300) ; while most 

 bast fibers are between i and 2 mm. in length, they may be more 

 than 200 mm. in length, as in Boehmeria nivea. The ends may 

 be more or less obtuse, or drawn out to a fine point ; occasionally 

 they are somewhat branched. The pores in surface view are nar- 

 row-elliptical and are arranged according to a left-handed spiral. 

 The spiral arrangement of the component elements of the wall 

 is supposed to give strength to the fibers, and, according to 

 Schwendener, they will sustain a weight nearly equivalent to that 

 sustained by wrought-iron and steel. 



Bast fibers may be isolated by the use of Schulze's macerating 

 fluid (which is prepared by dissolving a few crystals of potassium 

 chlorate in nitric acid) and moderately heating the solution con- 

 taining the material either on a slide or in a test tube. 



Wood fibers are sclerenchymatous fibers occurring in the 

 wood and are usually associated with tracheae. They give a more 

 or less distinct reaction for lignocellulose. They occur more 

 frequently than bast fibers (gentian being one of the few drugs 

 in which they are wanting) but seldom attain the length of the 

 latter. They are not infrequently branched at. the ends, and 

 besides a thin protoplasmic layer, they usually have no other 

 contents than water and air. They frequently have the yellowish 

 color, characteristic of stone cells, and also exhibit a similar 

 lamellation and refraction of the wall (Fig. 104). 



Conducting cells or mestome include those cells which are 

 chiefly concerned in the transferral of either crude or assimilable 



