52 
HISTOLOGY OF VEGETABLES. 
the hairs are plainly exhibited. 
In the husk of a grain of wheat, 
Fig. 36, not only the cells of 
the cuticle and layers of cells 
beneath, but also the fibres of 
the spiral vessels are silicified. 
The smooth, glassy outer sur- 
face which many of the varieties 
of cane present, is entirely due 
to silica ; for if a thin slice of 
the cuticle be removed and ex- 
posed to the flame of a blow- 
pipe, or to the action of nitric 
acid as in Fig. 37, from the 
Manilla cane, not only every 
cell of the cuticle remains 
beautifully defined, but in this 
instance, the layer of cells im- 
mediately beneath; these have 
no nuclei, and are seen at the 
bottom of the figure, the cuticular layer having been 
removed from this part. 
Of all the grasses used as food by man, rice contains 
the largest proportion of silica. This is demonstrated 
by boiling the husk of the rice grain in nitric acid to 
remove the organic matter, after which the microscope 
gives evidence of the large quantity of silica contained in 
the husk. This circumstance accounts for the worn 
and flattened surfaces of the teeth of those races of men 
FIG. 36 . 
A portion of the husk of a grain 
of Wheat. 
fig. 37 . 
A portion of the cuticular and 
subcuticular layer of cells of the 
Manilla cane. 
