42 
HISTOLOGY OF VEGETABLES. 
comes over, and the residue is known as the “ black” or 
“fiddler’s resin.” If, however, water be added prior to the 
distillation, the residue is the white resin of commerce. 
Canada balsam now so largely used for mounting 
microscopic objects, is an example of a liquid resin. 
Raphides. — Besides the various contents of cells 
which have already occupied our attention, there are 
certain mineral substances commonly found in them in 
the form of crystals. These were first noticed by 
Malpighi, in the Opuntia; and were subsequently de- 
scribed by Jurine and Raspail. They occur principally 
in two forms, either in stellate masses, as shown in 
Fig. 27, B, c, or in bundles of sharp-pointed crystals, 
very much resembling needles, as in Fig 27, A. It is 
these last which have obtained for themselves and their 
fellows the general name of raphides, from the Greek 
Fa,(pi$, a needle. They are also not unfrequently found 
as single crystals, in the form of octohedra, rectangular, 
and oblique prisms. According to Raspail, the needle- 
shaped, or acicular, are composed of phosphate, and the 
stellate of oxalate of lime. There are others having- 
lime as a base combined with tartaric, malic, or citric 
acid. These are easily destroyed by acetic acid, and are 
also very soluble in many of the fluids employed in the 
conservation of objects. Some of them are as large 
as / 0 th of an inch, others as small as ^th ; they occur 
in all parts of the plant, in the stem, bark, leaves, stipules, 
sepals, petals, fruit, root, spiral vessels, and even in the 
pollen. They are always situated in cells, and not as 
