44 
HISTOLOGY OF VEGETABLES. 
FIG. 28 . 
cells are detected immediately beneath the cuticular layer, 
filled with bundles of acicular crystals. 
In the cuticle of the 
Onion , every cell is occu- 
pied by an octohedral or 
prismatic crystal of oxalate 
of lime. In one specimen, 
Fig. 28, A, the octohedral 
form predominates ; where- 
as, in others, Fig. 28, b, 
the crystals are chiefly pris- 
matic, and are beginning 
to form stellate groups. 
All who are in the habit 
of examining the deposits 
from urine must be fami- 
liar with the appearance of 
the crystals of oxalate of 
lime, and will readily re- 
cognize their close resem- 
blance to these in the cells 
of the Onion. I have also met with them in the urine, 
contained in the interior of cells, so that, both in the 
animal and vegetable kingdoms, we have crystals of 
oxalate of lime as a product of cell secretion. 
Raphides of oxalate of lime are found in very great 
abundance in the medicinal Rhubarb , as shown in 
Fig. 27, c; the best specimens from Turkey, containing 
as much as thirty-five per cent, of them, those from the 
a, octohedral crystals of oxalate of 
lime in the cells of an Onion, b, pris- 
matic crystals of oxalate of lime in 
the cells of another part of the same 
Onion. 
