QuEKETT on the Rapliides of Cactus enneagonus. 
23 
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 both of oxalic and phos- 
phoric acid, and at the end of three days crystals were found 
in the cells in both instances, those of the oxalic acid being of 
the stellate and those in the phosphoric acid being of the 
rhombohedral form. None of the acicular, however, were 
ever present, although the process was continued for ten days. 
One of these pieces of rice paper I now show you, and a 
stellate mass of crystals is very plainly to be seen in the centre 
of the field — each precisely resembles the raphides found in 
rhubarb. 
The above description, which is a modification of that given 
in my lectures, well applies to the raphides in most plants, 
but the case will appear to be a little different in those plants, 
such as the cacti, which live to a great age, and in which the 
crystalline matter is in the greatest abundance. Whilst 
working at this subject about twelve months since I was in- 
duced to examine the raphides of a species of Cactus termed 
enneagonus, a specimen of which had been given me by a 
friend as abounding in crystals. This specimen 1 have with me, 
just as I received it, the part containing the crystals being about 
thirty-nine years old ; that they are very numerous, and at the 
same time very large, may be known by their being visible to 
the naked eye. If any of these raphides be examined in fluid 
with a power of at least 100 diameters, they will appear to be 
made up of crystals (as far as their external surface is con- 
cerned), which project outwards in the form both of sharp 
pointed and truncated prisms ; and if the centre be brought 
into focus this part will be found more opaque than the rest, 
and to be of a circular figure like a nucleus. If the masses be 
mounted in Canada balsam before they are examined they 
will then present one or other of the appearances given in 
Plate III. figs. 1, 2, 3, 4 ; some, as in fig. 1, will show a nucleus 
surrounded by concentric laminae of a brown colour ; others, as 
in fig. 2, will exhibit a spot like a nucleus, first surrounded by 
concentric laminae, but towards the margin the laminae become 
irregular, and the margin itself is composed of prismatic 
flattened crystals, not clear and transparent, but more or less 
granular, whilst some other specimens, as shown in figs. 3 and 
4, are made up almost entirely of the prismatic crystals, with 
little or no trace of concentric lamination. Having found this 
to be the case I was anxious to ascertain the chemical com- 
position of these so-called raphides, and for the purpose I 
tried the action of various re-agents upon them, and noticed 
that the crystals were slowly dissolved in dilute hydro-chloric 
