STRUCTURE.] ORIGIN. 109 



however, which succeeded was, to connect a vessel containing 

 a solution of oxalate of ammonia with one containing lime 

 water, by means of a few fibres of cotton : this gradual intro- 

 duction of one fluid to the other formed perfect crystals of 

 oxalate of lime on the ends of the fibres which were in con- 

 tact with the lime water. This having succeeded, another 

 attempt was made to form them in the interior of the cells of 

 such plants as did not previously possess them : some diffi- 

 culty occurred in finding any one fitted for the purpose, and 

 at last Rice-paper, as it is termed, (the concentric slice from 

 the pith of ^Eschynomene and Hibiscus,) was selected as the 

 best material for the experiment, from its admitting an ex- 

 amination of their formation, by becoming transparent when 

 charged with fluid. 



This substance was placed in lime water under an air 

 pump, and the cells were soon filled with that fluid ; it was 

 then dried and submitted two or three times to the same 

 process : by this means the cells were well charged with lime. 

 Portions of this substance were placed in weak solutions of 

 oxalic and phosphoric acids, and allowed to remain. On the 

 third day, when examined, the cells in both instances con- 

 tained much precipitate, together with numerous crystals; 

 those in the oxalic acid being precisely like the conglomerate 

 form in Rhubarb, and those in the phosphoric being rhombo- 

 hedra, but none of the acicular shape were found, even after 

 continuing the process beyond eight or ten days. 



These experiments distinctly prove the origin of Raphides, 

 which appear to be compounds that become crystallised 

 merely by the slow admixture of their constituents, and are 

 probably modified by gummy, amylaceous, and other matters 

 which are contained in the juices of the plant. Their for- 

 mation does not seem confined to living structures or to any 

 particular tissues or organs of a plant ; but the process may 

 be carried on in any situation, as can be proved in the Grape 

 vine, in which crystals can be discovered in every organ, and 



in the vascular as well as in the cellular tissue. 







A very peculiar view of the origin of Raphides has been 

 taken by M. Pay en, who has turned his attention to certain 



