22 



VEGETABLE PHYSIOLOGY. 



[LESSON 7. 



134. If the thin, transparent, and dried outer layer of a 

 FIQ 2T ripe onion be submitted to the mi- 



croscope, a beautiful assemblage of 

 crystals of this newly formed miner- 

 al will be seen in the cells respec- 

 tively (Fig. 27). 



135. These are sometimes octa- 

 gonal ; frequently prismatic. 



136. When the lime has been suf- 

 ficiently abundant, and the fruit is 

 well developed, and of large size, 

 it is usual to find more than one 

 crystal in a cell; whenever this oc- 

 curs, they always form crosses, sometimes composed of two, fre- 

 quently of a plurality of crystals. 



137. The root of the Pie-plant (Ehubarb) con- 

 tains a vast number of stellate crystals of oxalate of 

 lime. (Fig. 28.) 



138. The common English rhubarb, so abun- 

 dantly cultivated in our Gardens, and offering such a 

 delicious, and highly nutritive material for pies and 

 tarts, in advance of all other fruits, contains a far less 

 amount of this mineral than the Turkey Rhubarb, so 

 valuable as a medicine. In the latter, it exists to so 



FIG. 31. 



Raphides ; Onion containing prismatic crys- 

 tals of Oxalate fluid. 



FIG. 23. 



Eaphides, Rhubarb. 



FIG. 29. 



Melon Cactus, the cells of Encephalatus pungens, containing starch and 



which contain raphides. raphidian cells. 



