40 
HISTOLOGY OF VEGETABLES. 
to judge of its quality ; he was rendered uncomfortably 
ill for two or three days. 
Nor is it in the animal and vegetable kingdoms alone 
that we meet with oil, since it has also been obtained 
from the mineral kingdom. Mineral oil derived from 
bitumen is of a dark colour, somewhat resembling 
brandy, and burns exceedingly well in lamps. The 
paraffine extracted from peat by destructive distillation, 
by Mr. Owen’s process, is employed for making candles. 
Peat appears to be capable of conversion into a great 
variety of useful products, many of which are at this 
time gaining much attention from practical men. 
Volatile Oils are also secreted in cells, which, from 
their peculiarities of shape and situation, have received 
the names of vesicles, vittse, glands, &c. They occur on 
the surface or in the parenchyma of leaves, and in the 
pericarp of fruits. They are not nutritious, are soluble in 
alcohol, but not in water. The volatile oil of the rind 
of the lemon and orange, is contained in such vesicles, 
and connoisseurs in punch are well aware, that by rubbing 
a lump of sugar over the outer surface of the lemon, the 
sugar absorbs the essential oil, and thus imparts a fine 
flavour to the liquor ; the sugar being rough acts the 
part of a grater, rupturing the cells in which the oil is 
contained, and allowing it to escape. 
Many of these essential oils, when evaporated, yield a 
resinous substance. The resin may be sometimes seen 
on the surface of plants yielding a perfume. There is a 
striking example of this in the seed of the common 
