34 RAPHIDES. 
of plants, although the term raphides (which is the Greek for 
needles) was originally given to those only that had the form 
of a needle (figs, 56 and 57). Raphides may be found more 
or less in nearly all orders of plants, and in all their organs ; 
generally, however, they are most abundant in the stems of 
herbaceous plants, in the bark of woody plants, and in leaves 
and roots. In some plants they occur in such enormous quan- 
tities that they exceed in weight the dried tissue in which they 
are deposited: this may be specially observed in some Cactacez ; 
thus Edwin Quekett found in the dried tissue of the stem of 
the Old-man Cactus (Cereus senilis) as much as 80 per cent. of 
crystals. Professor Bailey also found in a square inch of Locust 
bark of the thickness of ordinary writing paper, more than a 
million and a half of these crystals. The dried root of that kind of 
Rhubarb now known as China Rhubarb, commonly contains 
from 35 to 40 per cent., and hence when chewed it is very 
Fia. 56. 
Bre. 54. Fre. do. 
esi) CRF 
lml 
Fig. 54. Solitary crystals or raphides in the cells of the inner bark of the 
Locust tree. After Gray. Fig. 55. Conglomerate raphides or sphz- 
raphides of the Beet. Fig. 56. Acicular or true raphides of a species 
of eee Two cells contain raphides, and three of them chlorophyll 
granules, 
gritty ; and as this variety of Rhubarb usually contains a larger 
proportion of raphides than other kinds, this grittiness has been 
employed as one means of distinguishing it from them. The 
raphides are usually contained in cells, in which starch, chloro- 
phyll, and other granular structures are absent (fig. 56), although 
this is by no means necessarily the case. These crystals are more 
commonly found in the cavities of the cells, but they also occur 
in their walls; in all cases, however, they are mineral salts 
which have crystallised naturally out of the cell-sap. They 
may be especially found in the walls of cells in the Coniferze and 
Gnetaceze. 
The raphides occur either singly in the cells, as in those of 
the inner bark of the Locust tree (fig. 54); or far more commonly 
there are a number of crystals in the same cell. In the latter 
case they are usually either placed side by side, as in the stem 
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