our.

313. OLEA EUROPAEA.--The European olive, which is popularly supposed to
furnish _all_ the olive oil of commerce. It is a plant of slow
growth and of as slow decay. It is considered probable that trees
at present existing in the Vale of Gethsemane are those which
existed at the commencement of the Christian era. The oil is
derived from the flesh of the fruit, and is pressed out of the
bruised pulp; inferior kinds are from second and third pressings.
The best salad oil is from Leghorn, and is sent in flasks
surrounded by rush-work. Gallipoli oil is transported in casks,
and Lucca in jars. The pickling olives are the unripe fruits
deprived of a portion of their bitterness by soaking in water in
which lime and wood ashes are sometimes added, and then bottled in
salt and water with aromatics.

314. OPHIOCARYON PARADOXUM.--The snake nut tree of Guiana, so called on
account of the curious form of the embryo of the seed, which is
spirally twisted, so as to closely resemble a coiled-up
blacksnake. The fruits are as large as those of the black walnut,
and although they are not known to possess any medical properties,
their singular snake-like form has induced the Indians to employ
them as an antidote to the poison of venomous snakes. The plant
belongs to the order of _Sapindaceae_.

315. OPHIORRHIZA MUNGOS.--A plant belonging to the cinchona family, the
roots of which are reputed to cure snake bites. They are intensely
bitter, and from this circumstance they are called earth-galls by
the Malays.

316. OPHIOXYLON SERPENTINUM.--A native of the East Indies, where the
roots are used in medicine as a febrifuge and alexipharmic.

317. OPUNTIA COCHINELLIFERA.--A native of Mexico, where it is largely
cultivated in what are called the Nopal plantations for the
breeding of the cochineal insect. This plant and others are also
grown for a similar purpose in the Canary Islands and Madeira.
Some of these plantations contain fifty thousand plants. Cochineal
forms the finest carmine scarlet dye, and at least there are 2,000
tons of it produced yearly, in value worth $2,000 per ton.

318. OPUNTIA TUNA.--This plant is a native of Mexico and South America
generally. It reaches a height of 15 to 20 feet and bears
reddish-colored flowers, followed by