42 
PLANT MORPHOLOGY. 
The Collenchyma cells are long cells (occasionally 2 mm. 
long) which are thickened at the corners or intercellular 
spaces. The walls consist of cellulose, or a modifica- 
tion of it, known as collenchym, and have a silvery 
or grayish-blue luster. Besides the organized contents 
these cells occasionally contain starch They are found 
directly beneath the epidermis of herbaceous stems, 
petioles, and the midrib of various leaves, and are 
particularly noticeable at the angles of all stems that 
are ribbed or angled in transverse section. 
Sclerenchyma cells include all of those cells which 
have more or less uniformly thickened walls consisting 
of lignocellulose and permeated by simple or branching 
pores. They have a thin layer of protoplasm and rela- 
tively large vacuoles, which contain tannin or tannin- 
like masses, and occasionally calcium oxalate crystals or 
starch, and upon the death of the cell the lumen contains 
air. Two kinds of sclerenchyma are recognized : one 
in which the cells are more or less isodiametric, known 
as stone cells (short sclerenchyma or sclereiden) ; and 
another in which the cells are elongated, being from 
•5 to 2 mm. long, as a rule, known as sclerenchyma fibers 
(or long sclerenchyma). Of these, two kinds are dis- 
tinguished, chiefly according to their position in the 
plant, namely, bast fibers and wood fibers (or libri- 
form). Seldom are the wood and 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 monocotyledenous 
roots, and the term sclerenchymatous is here best em- 
ployed. In the study of powdered drugs the term scleren- 
chymatous fiber may be employed with advantage 
when speaking of wood and bast fibers, as in this con- 
dition they are not readily distinguishable. 
Stone cells are usually polygonal, or more or less 
