CELL-CONTENTS AND FORxMS OF CELLS. 267 



permeated by simple or branching pores. They have a thin layer 

 of protoplasm enclosing large vacuoles, and may contain tannin 

 or tannin-like masses, and occasionally calcium oxalate crystals 

 or starch, and in dead cells the lumen or cell cavity contains 

 air. Two kinds of sclerenchyma are recognized : i, in which the 

 cells are more or less isodiametric (Figs. 136-138), known as 

 stone cells (short sclerenchyma) ; and 2, in which the cells 

 are elongated (Figs. 139-141), being from 0.5 to 2 mm. in 

 length and known as sclerenchymatous fibers (or long scleren- 

 chyma). Of these latter, two kinds are distinguished, chiefly 

 according to their position in the plant, namely, bast fibers, or 

 stereome, and wood fibers, or libriform. Seldom are the wood and 



Fig. 137. Several forms of stone cells: A, white oak bark; B, white cinnamon or 

 canella bark (Canella alba); C, seed-coat of capsicum. 



bast fibers in the same plant uniform in structure and composition, 

 as in glycyrrhiza and althaea. On the other hand, they are with 

 difficulty distinguished in monocotyledonous roots, and the term 

 sclerenchymatous fiber is here best employed to include both kinds 

 of cells. In the study of powdered drugs the term sclerenchyma- 

 tous fiber may be employed with advantage when speaking of wood 

 and bast fibers, as in this condition they are not readily distinguish- 

 able. It is usual in plant anatomy to include as stereome all ligni- 

 fied fibers not directly associated with the vessels of the mestome 

 strands (or vascular bundles). 



Stone cells or sclerotic cells are parenchymatous cells 

 with very thick, lignified walls, composed of numerous lamellae, 



