7 ° 
PHARMACEUTICAL BOTANY 
Collenchyma. — This form of tissue is characterized by its cells 
being prismatic, more elongated than ordinary parenchyma, and 
thickened in their angles with a colloidal substance. The cells, 
like those of parenchyma tissue contain protoplasm and a nucleus, 
and frequently chloroplasts. Collenchyma is generally found 
underneath the epidermis, and gives strength to that tissue. It is 
frequently observed forming the “ribs” of stems and fruits of the 
Fig. 21. — Stone cells from different sources, i. From coffee; 2, 3, and 4, 
from stem of clove; 5 and 6, from tea leaf; 7, 8, and 9, from powdered star-anise 
seed. ( Stevens , after Moeller.) 
Umbelliferce and “ribs” of stems of the Labiates. In many leaves 
it has been found as the supporting and strengthening tissue between 
the stronger veins and the epidermis. 
Sclerenchyma or stony tissue comprises a variety of supporting 
elements having thickened cell walls composed of lignocellulose. 
When first formed these cells resemble those of ordinary parenchyma 
in having walls of pure cellulose, but later lignin becomes deposited 
on the inner surface of the walls in one or more layers. (Occasion- 
ally as in the rhizomes of Ginger no lignin is deposited on the walls 
