JRYSTALS OR RAPHIDES. 



59 



94. Crystals, or Raphides (Fig. 71-78). These exist in more or 

 less abundance in almost every plant, especially in the cells of the 

 bark and leaves, as well as in the wood and pith of herbaceous 

 plants. In an old stem of the Old-man Cactus (Cereus senilis), the 

 enormous quantity of eighty per cent of the solid matter left after 

 the water was driven off was found to consist of these crystals. In 

 the thin inner layers of the bark of the Locust, each cell contains a 

 single crystal, as is shown in Fig. 75. Professor Bailey, who has de- 

 voted particular attention to this subject, computed that, in a square 

 inch of a piece of Locust-bark, no thicker than ordinary writing-paper, 

 there are more than a million and a half of these crystals. There 

 is frequently a group of separate crystals in the same cell, or a con- 

 glomerate cluster, as in Fig. 76. The most common form is that 

 of a long and narrow four-sided prism, so slender that it resembles 

 a needle (Fig. 71-73), Such crystals were accordingly called 

 Raphides, i. e. needle-shaped bodies, — a name which has been ex- 

 tended to include all crystals in plants, of whatever shape. When 

 the crystals are needle-shaped, they usually occur in large numbers 

 in each crystal-bearing cell, packed together in a bundle. These 



FIG. 71. Raphides, or acicular crystals, from the stalk of the Rhubarb : three of the cells 

 contain chlorophyll, and two of them raphides. 



FIG. 72. Raphides of an Arum, contained in a large cell ; and 73, the same, detached from 

 the surrounding tissue, and discharging its contents upon the application of water. 



FIG. 74. Crystals from the base of an onion, one of them a hemitrope or double. 



FIG. 75. Crystals of the inner bark of the Locust. 



FIG. 76. A glomerate mass of crystals from the Beet-root. 



FIG. 77,78. Crystals from the bark of Hickory. Figures 73-78, and also 69, are from 

 sketches kindly supplied by the late Professor Bailey of West Point. 



