176 HJSTOLOGY or 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 ca\dty, 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. i), 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. 



