8 4 
PHARMACEUTICAL BOTANY 
SECRETION RESERVOIRS 
These structures are either found as globular or irregular spaces, 
as in Orange and Lemon Peel and Eucalyptus leaves, containing oil 
or oil and resin when they are called internal glands or, as tube-like 
spaces filled with hydrocarbon principles such as are found in Pine 
leaves and stems, when they sometimes receive the name of secretion 
canals. Occasionally they are named according to the nature of 
their contents — resin or oil canal or reservoir, etc. They are gen- 
erally lined with a layer of cells, usually more or less flattened, which 
are characterized by possessing large nuclei. To this layer has been 
assigned the name “epithelium.” 
Fig. 33. — Resin duct (secretion reservoir) in leaf of Pinus silvestris, in cross 
section at A , and in longitudinal section at B ; h, cavity surrounded by the secret- 
ing cells;/,/, sclerenchyma fibers surrounding and protecting the duct. ( Stevens , 
after Haberlandt.) 
Classification of Tissues According to Function.— According to 
their particular function, tissues may be classified as follows: 
I. Conducting Tissue 
II. Protective Tissues 
III. Mechanical Tissues 
’ Parenchyme (fundamental tissue) 
Xylem cells (wood parenchyme) 
Tracheae (ducts) 
Phloem cells 
Sieve tubes 
. Companion cells 
I Epidermis (outer cell walls cutinized) 
l Cork (suberized tissue) 
Bast fibers 
Wood fibers 
Sclerenchyme fibers 
Stone cells 
