=Magnesium=, _n._ A metal, very abundant in sea water and in the earth’s crust. Also found in the composition of animals and some plants. =Mandrake=, _n._ A plant with umbrella-like leaves and a yellow, juicy fruit as large as an egg. =Microscope=, _n._ From two Greek words meaning “small” and “view”; an instrument which magnifies and renders visible bodies too small to be seen by the naked eye. =Moth=, _n._ An insect resembling a butterfly. Moths have no knobs on their antennæ, or “feelers,” and butterflies have. =Mullein=, _n._ A tall, stout weed with thick, wooly leaves. N. =Naiads=, _n._ In Greek and Roman mythology, water nymphs. Beautiful young goddesses presiding over springs and streams. =Nasturtium=, _n._ L. _nasus_, nose, _tortus_, convulsed; the name of a plant, so called because of its acrid juice that causes a stinging sensation at the back of the nose when it is tasted. =Nectar=, _n._ The drink of the gods on Mt. Olympus. The honey of flowers. =Nectaries=, _n._ The receptacles in which the nectar of flowers is collected; also the gland which secretes the nectar. =Neptune=, _n._ In Roman mythology, the god of the sea. =Nettle=, _n._ A weed armed with stinging hairs. =Nitrogen=, _n._ A colorless, odorless, tasteless gas, forming about three-fourths of the air and necessary to the formation of all living bodies, whether plant or animal. =Nitrogenous substances=, _n._ Substances in which nitrogen is one of the constituents. =Node=, _n._ L. _nodus_, a knot; the part of a stem which bears a leaf or leaves. It is often a little larger than the rest of the stem. O. =Octavus=, _n._ L. _octavus_, eighth; given in this book as a name to a suppositional plant. =Oil=, _n._ From a Greek word meaning “olive oil.” An inflammable, greasy liquid extracted from certain vegetables, as olives, cotton seeds, nuts, etc. =Olive oil=, _n._ The oil expressed from the fruit of the olive tree. =Orient=, _n._ L. _oriens_, rising, as the sun; the East, the part of the horizon where the sun rises; Eastern countries, particularly Turkey, Persia, Egypt, India, China, etc. =Ovary cells=, _n._ The cells which build up the ovary. =Ovule=, _n._ L. _ovum_, an egg; a little egg. Applied to the rudimentary seeds of plants, which, upon fertilization and growth, become true seeds. =Ovule cells=, _n._ The cells of which the ovule is formed. =Oxalis=, _n._ From a Greek word meaning “acid”; a well-known plant, one form of which is called “wood sorrel.” It is called oxalis because of its acid juice. =Oxygen=, _n._ One of the gases that compose the air and which is essential to life. It is also found in composition in the tissues of plants and animals. P.