MORPHOLOGY OF HIGHER PLANTS. 



187 



contains air. Two kinds of sclerenchyma are recognized: one in 

 which the cells are more or less isodiametric, known as stone 

 CELLS (short sclerenchyma) (Figs. 301 and 302) ; and another 

 in which the cells are elongated, being from 0.5 to 2 mm. long, as a 

 rule, and known as sclerenchyma fibers (or long scleren- 

 chyma) (Figs. 104, 299, 300). Of these latter, two kinds are dis- 

 tinguished, chiefly according to their position in the plant, namely, 

 bast fibers and wood fibers (or libriform). Seldom are the wood 



L "% 



Fig. 103. Bordered pores of the tracheids of the wood of Abies alba as viewed in 

 longitudinal section: m, middle lamella; v, i, middle and inner layers of walls of contigu- 

 ous cells ; C, pore-canal through which sap passes from one cell to another ; L, dome- 

 shaped cavity of pore; S, -separating wall or closing membrane which is usually thickened 

 in the middle-as sho-wn at t. In older cells the separating membrane is broken as shown 

 in the lower pore in figure 2, At the right in figure 4 is shown a surf ace view of a bordered 

 pore, the dotted lines indicating the relation of the circles to the structure of the pore. — 

 After Vogl. 



and bast fibers in the same plant uniform in structure and compo- 

 sition, as in gly.cyrrhiza and althasa. On the other hand, they are 

 with difficulty distinguished in monocotyledonous roots, and the 

 term sclerenchymatous is here best employed to include both kinds 

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

 matous fiber may be employed with advantage when speaking of 

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

 distinguishable. 



