LESSON 7.] 



RAPHIDES. 



23 



great extent, that the only test for this root, as compared with the 

 English, which is frequently substituted for it, is to chew a small 

 piece of it, when if it be found particularly gritty (occasioned by the 

 crystals of oxalate of lime), its identity is assured. 



139. Crystals of oxalate of lime, of the stellate form, are also 

 found in the Beet-root (Fig. 29), the melon cactus (Fig. 30), and (to- 

 gether with starch) in a Cycadaceous plant (Encephalartus pungens) 

 (Fig. 31). The bulb of the Squill plant (Squilla maritima) (Fig. 32) 

 contains raphides. 



140. Oxalic is not the only acid found combined with lime to 



FIG. 



FIG. 33. 



Squilla maritima. 



Cells of Kumex, containing raphides. 



form raphides in the plant ; on the contrary, phosphoric, malic, sul- 

 phuric, and carbonic acids, all contribute to the varied forms of these 

 crystals. 



141. Phosphate of lime generally produces acicular crystals (a), 

 FIG. 34. as seen in the cells of Rumex 



(Rhubarb) (Fig. 33) ; the leaf of 

 the maple also affords similar crys- 

 tals (Fig. 34). 



142. So wonderfully abundant 

 are raphides in certain plants, that 



Cells of Maple leaf, containing raphides. the kte p rof> Bailey (of Weflt 



Point) computed in a square inch of Locust-bark, the thickness of 

 writing paper, more than a million and a half of these crystals ! 



143. Certain species of the Cactus tribe of plants contain such 

 an inordinate quantity of raphides that they appear to be almost en- 

 tirely made up of them ; sometimes every cell of the cuticle contains 

 stellate crystals, whereby these plants are rendered exceedingly brit- 



