MICROSCOPIC OBJECTS. 



Fig. 177. Raphides from the Hyacinth (Hyacinthus orien- 

 talis), x20Q. 



Raphides are minute crystals, chiefly found in the cellular 

 tissue of plants ; they are most abundant in the Natural 

 Orders Liliacese, Cactacese, Polygonaceae, Orchidacese, &c. 

 Most of the forms show well under polarized light. They 

 are composed of the various salts of lime, viz. the oxalate, 

 carbonate, sulphate, and phosphate of lime. The following 

 tests for these raphides may be useful : Upon the appli- 

 cation of a small drop of acetic acid, the presence of the 

 phosphate or carbonate is immediately perceived, as both 

 of these salts dissolve with effervescence, while neither the 

 oxalate nor the sulphate is altered : for their tests, see 

 fig. 179. To distinguish the phosphate from the carbonate, 

 an excess of ammonia must be added, when, if phosphate 

 of lime is present, it will be developed as minute granular 

 matter. 



Fig. 178. Raphides from Turkey Rhubarb (Rheum pal- 

 matum), x 200. 



These raphides consist of oxalate of lime, each stellate 

 group being composed of a number of rectangular crystals, 

 so arranged by the natural deposition of the salt in any 

 single cell as to partake of the stellate form. An artificial 

 formation of these stellate crystals may be obtained by placing 

 rice-paper or elder-pith in a solution of chloride of calcium, 

 exhausting the air in the cells by placing under an air-pump, 

 then straining off the chloride, and adding a saturated solution 

 of oxalic acid ; after which, occasional stellate crystals will 

 be found. This experiment may be tried with the other 

 salts of lime. 



Raphides are best seen when mounted in Canada balsam. 



