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A TEXT-BOOK OF BOTANY 



which are permeated with simple and not infrequently branching 

 pores. They vary in form, being usually polygonal, or more or 

 less irregular in outline, sometimes branching. The lamellation of 

 the walls is brought out by the use of swelling reagents, as solu- 

 tions of the alkalies, hydrated chloral, chromic acid, etc. In 

 typical stone cells the walls always give the characteristic re- 

 action for lignocellu'ose with acid solutions of either phloro- 

 glucin or aniline sulphate. The lumina of the cells frequently 

 contains a reddish, amorphous substance, seldom are crystals of 

 calcium oxalate present (Fig. 136, H), and not infrequently they 

 are filled with air (Fig. 136, G). In the identification of com- 



FiG. 138. Various forms of stone cells in star anise, the fruit of Illicium anisatum. 



mercial products the study of the contents of the stone cells is 

 frequently as important as that of the forms of cells. 



Bast fibers or stereomatic cells are sclerenchymatous 

 fibers, occurring in the bark and usually associated with sieve cells. 

 They represent the skeleton of plants and are the most important 

 mechanical tissues of the bark, being much firmer than the collen- 

 chyma. They are very long, spindle-shaped, with more or less 

 thick walls, and provided with slit-like, oblique pores. The walls 

 may consist of cellulose, as in the fibers of flax, but they are 

 usually more or less lignified ; the lumina is narrow and usually 

 contains air. In transverse sections the fibers are more or less 



