CRYSTALS 



59 



(cf . p. 144) ; also in the leaves of deciduous plants, just prior 

 to leaf -fall, features which respectively emphasise that this 

 substance is a by-product, and that it is not generally useful to 

 the organism. 



FIG. 25. Crystals. A, Cluster crystals from leaf of Dog's Mercury (Mer- 

 curialis). B, Raphides from leaf of Enchanter's Nightshade (Circcza). 

 C, Solitary crystals from phloem of Horse Chestnut (JEsculns). 



The crystals of calcium oxalate are not soluble in acetic acid, 

 but readily dissolve in sulphuric acid, with the production of 

 calcium sulphate. The latter, being itself insoluble, becomes 

 deposited promiscuously in the form of needle-like crystals. These 

 tests serve to verify the presence of oxalate of lime, but in most 



