Mucilage cavities are not of common occurrence in medicinal plants. They occur, however, in the stem and root bark of sassafras, the stem bark of slippery elm, the root of althea, etc.
CHAPTER VIII
STORAGE TISSUE
Most drug plants contain storage products because they are collected at a period of the year when the plant is storing, or has stored, reserve products. These products are stored in a number of characteristic ways and in different types of tissue.
The most important of the different types of storage tissue that occurs in plants are the storage cells, the storage cavities, and the storage walls.
STORAGE CELLS
Several different types of cells function as storage tissue. These cells, which are given in the order of their importance, are parenchyma, crystal cells, medullary rays, stone cells, wood fibres, bast fibres, and epidermal and hypodermal cells.
CORTICAL PARENCHYMA
Cortical parenchyma of biennial rhizomes, bulbs, roots, and the parenchyma of the endosperm of seeds store most of the reserve economic food products of the higher plants.
Pith parenchyma of sarsaparilla root (Plate 65, Fig. 4) and the pith parenchyma of the rhizome of memspermun, like the pith parenchyma of most plants, function as storage cells.