176 HISTOLOGY OF MEDICINAL PLANTS 
crystals, while the parenchyma cells of the cortex of sarsaparilla 
and false unicorn root contain bundles of raphides. In every case 
observed the raphides are surrounded by mucilage. This is true 
of squills, sarsaparilla, false unicorn, etc. When cells with 
raphides and mucilage are mounted in a mixture of alcohol, 
glycerine, and water, the mucilage first swells and finally dis- 
appears. 
STORAGE CAVITIES 
Particular attention should be given to storage cavities 
whenever they occur in plants, for the reason that they are 
usually filled with storage products, and for the added reason 
that storage cavities are not common to all plants. Storage 
cavities occur in roots, stems, leaves, flowers, fruits, and seeds. 
CRYSTAL CAVITIES 
Characteristic crystal cavities occur in many plants. Such 
a cavity containing a bundle of raphides is shown in the cross- 
section of skunk cabbage leaf (Plate 67). 
SECRETION CAVITIES 
In white pine bark there are a great number of secretion 
cavities which are partially or completely filled with oleoresin. 
In the cross-sections of white pine bark the secretion cavities 
are very conspicuous, and they vary greatly in size. This 
variation is due, first, to the age of the cavity, the more re- 
cently formed cavities being smaller; and secondly, to the 
nature of the section, which will be longer in longitudinal section, 
which will be through the length of the secretion cavity, and 
shorter on transverse section. Such a section shows the width 
of the secretion cavity. 
Characteristic mucilage cavities occur in sassafras root, stem 
bark, elm bark (Plate 66, Fig. 1), marshmallow root, etc. 
These cavities form a conspicuous feature of the cross-section 
of these plants. The presence or absence of mucilage cavities 
in a bark should be carefully noted. 
LATEX CAVITIES . 
The latex tube cavities are characteristic in the plants in 
which they occur. These cavities as explained under latex 
tubes are very irregular in outline. 
