CELLS. RAPHIDES. 
47 
plant from the soil. Many of the larger kinds of 
raphides, as those from the Cactus , Fig. 27, b, do 
not consist entirely of earthy material, if they be 
acted on by an acid just strong enough to dissolve 
the lime, it will be found that an organic basis is 
left behind retaining, to a certain extent, the shape 
of the mass of crystals. Some of the masses even 
exhibit a laminated centre with crystals on their ex- 
terior, and when mounted in Canada balsam , they 
very much resemble small calculi, leading one to sup- 
pose that this was their true nature. They may, how- 
ever, be formed artificially, and my late brother 
succeeded in doing so in the following manner : If 
oxalic or phosphoric acid be added to lime-water, the 
precipitate will be pulverulent and opaque. If, however, 
a vessel containing oxalate of ammonia in solution be 
connected by means of a few T filaments of cotton, with 
another vessel containing lime-water ; crystals will be 
formed at the end of the fibres in contact with the 
lime-water. This led him to attempt to form them in 
the interior of cells. He selected for the purpose a 
portion of rice-paper ; this substance was placed in lime- 
water under an air-pump, in order to fill the cells with the 
fluid. The paper was then dried, and the process again 
and again repeated, until many of the cells were 
charged with lime-water. Portions of the paper' were 
then placed in weak solutions of oxalic and phosphoric 
acid, and at the end of three days, crystals were found in 
the cells in both instances, those in the oxalic acid being 
