_Monadelphous._ With the stamen filaments in a single bundle. _Moniliform._ Jointed in such a way as to resemble a necklace. _Monecious._ Hermaphrodite. Having male and female flowers on the same plant. _Monopoly._ Sufficient control to influence price. _Monotreme._ One of the lowest order (Monotremata) of mammals. _Monsoon._ A periodic wind. Specifically, such a wind in the Indian Ocean. _Moraine._ The mass of earth and other matter deposited by a glacier. _Morphology._ The study of form (of organisms or of words). _Motor._ Pertaining to a nerve and an impulse causing motion. Relating to action and the consciousness of action. Pertaining to a muscle causing action. A machine which causes motion, especially such an electric machine or one which is comparatively small. _Muscle._ A fibrous band or bundle which contracts to produce movement in an animal body. _Muscology._ The study of mosses. _Mutation._ A sudden variation which may produce a new species. _Mycology._ The study of fungi. _Myriapoda._ A class of arthropods including the centipedes. _Narcotic._ A substance which induces sleepiness. _Nascent._ Just beginning, having special properties because of just having been released from combination. _Neap tide._ The tide at which the high water mark is the lowest. _Nebular Hypothesis._ The hypothesis advanced by Laplace that (in the words of F. W. Dyson) “a vast nebula--diffused tenuous matter--once extended to the confines of the solar system, and under the influence of gravitation slowly contracted.... As the contraction proceeded the rotation necessarily increased, and rings or other masses were thrown off which collected and formed planets.” Any of several more or less similar hypotheses. _Nectar._ A sweet fluid produced by plants. _Neocene._ Relating to the later part of the Tertiary (geological) period. _Neodymium._ A metallic element. Symbol: Nd. _Neolithic._ Relating to the later part of the Stone Age. _Neon._ A gaseous element. Symbol: Ne. _Nerve._ The rib of a leaf. A vein. One of the fibers or bundles of fibers carrying impulses of sensation and motion. _Neurosis._ Activity of the nerves. A functional disease attributed to the nerves. _Neutral._ Neither acid nor basic in reaction. Without sex organs. _Nickel._ A metallic element. Symbol: Ni. _Niton._ A gaseous element which occurs in radium emanation. Symbol: Nt. _Nitrogen._ A gaseous element constituting about four-fifths of the air. Symbol: N. _Noble metals._ Metals which do not oxidize in air or oxygen. Among the noble metals are gold, silver, and platinum. _Node._ A knob or root or branch, where a leaf is usually borne. One of the points where the orbit of a planet or comet and the ecliptic meet. A point or line which is at rest in a vibrating body. _Normal._ Conforming to a standard or type. The normal is not necessarily superior to the abnormal. _Nutritive._ Of value as food.