RUTACEALS. 425 
inhabitant of the garden of the Dominicans, and is said to have 
been fifty feet high. 
The principle to which odoriferous plants owe the qualities 
which render them so useful at the toilet has received the name of 
essential or volatile oil. The oils, volatile or essential, are met 
with most habitually in the flowers and the leaves; very rarely in 
the fruit. It happens sometimes that distinct oils exist in the 
same plant. Let us take the Orange for example. The essence 
drawn from the flowers of the Orange is very different from that 
furnished by the leaves. The essence furnished by the leaf differs 
again from that produced by the fruit. 
The volatile oil is contained in the vesicles or cells which per- 
vade all its parts; and so completely are these enclosed, that the 
plants may be dried without divesting them of the odorous prin- 
ciple, which still remains in the cavities. In other cases, par- 
ticularly in the flowers, the essence forms itself on the surface of 
the organ, and is volatilised at the rate at which it is produced in 
the interior of the organs of the plant. 
The mode of extracting these essences varies according to their 
nature and condition. Some of them may be extracted by simple 
expression. This may be done with the essential oils of the 
Citron and the Orange, which reside in the rind or envelope of 
the fruit. ‘They are reduced to a pulp, adding water afterwards 
to the liquor produced by pressure, when the oil will swim on 
the surface of the water added. 
But the greater part of these essences are produced by distilla- 
tion. This process is performed by placing the leaves, flowers, 
or fruits of plants, with a sufficient quantity of water, in an 
alembic or still. The essential oils only enter into ebullition at a 
higher temperature than water, since their point of ebullition 
rises in general to 130° or 140° OC. Nevertheless the steam, which 
is renewed unceasingly, escapes so rapidly into space that it is 
condensed in the bosom of the alembic. Let us explain. The 
Vapour of the essential oils diffuses itself in the steam which fills 
the alembic, which, however, is condensed; a new supply of steam 
Succeeds, which in its turn is saturated with the vapour of the oil. 
_ 4n this manner we can explain the rapid and continued evapora- 
__ tion of oils which only enter into ebullition at 140° in steam 
