22 QuEKETT on the Raphides of Cactus enneagonus. 
tincture in which no raphides are contained is as efficacious 
as the powder. 
Some plants, as many of the cactus tribe, are made up 
almost entirely of raphides. In some instances every cell of the 
cuticle contains a stellate mass of crystals, in others the whole 
interior is full of them, rendering the plant so exceedingly 
brittle that the least touch will occasion a fracture, so much so 
that some specimens of cactus senilis, said to be 1000 years 
old, which were sent a few years since to Kew from South 
America, were obliged to be packed ip cotton, with all the 
care of the most delicate jewellery to preserve them during the 
transport, 
Raphides of peculiar figure are common in the bark of 
many trees. In the hiccory {Carya alba) may be observed 
masses of flattened prisms having both extremities pointed. 
Similar crystals are present in the bark of the lime-tree ; they 
occur in rows, their pointed extremities nearly touching each 
other, their principal situation being in the cellular tissue close 
to the medullary rays. Other forms of crystals, as the rhom- 
bohedron and a small stellate form, are also found in the bark 
of the lime. 
In vertical sections of the stem of Elosagnus angustifolia nu- 
merous raphides of large size may be seen in the pith. 
Raphides are also found in the bark of the apple-tree, and 
in the testa of the seeds of the elm ; each cell contains two or 
more very minute crystals. 
It is at present not known what office raphides perform in 
the economy of the plant : some have gone so far as to state 
that they are deposits to be applied towards the mineral part 
or skeleton of the plant ; but the fact of their being insoluble 
in vegetable acids would prove this view of their use to be 
erroneous. The more rational supposition is, that they are 
generally accidental deposits formed by the union of vege- 
table acids with lime or other base existing in the plant or 
taken up from the soil. They may, however, 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 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 in fill the cells with the fluid ; the paper was then dried, 
