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MAASTRICHTIAN AGE The Maastrichtian age was the last part of the Cretaceous period, about 71 to 65 million years ago, at the very end of the Mesozoic Era.	MAGNETIC FIELD The Earth's magnetic field is aligned with the north and south poles, and has reversed many times during geologic history. A fossil's magnetic orientation can give clues to its date.	MALM EPOCH The Malm epoch was the late (or upper) part of the Jurassic period, about 159 to 144 million years ago.
MANGROVE Mangroves are tropical evergreen trees and shrubs. They live near the shore in tropical marshes and tidal shores with their adventitious roots in the salt water. Classification: genus Rhizophora. Some mangroves include the red mangrove (Rizophora mangle), the black mangrove (Avicennia germinans), and the white mangrove (Laguncularia racemosa).	MANGROVE FOREST A mangrove forest (also called a mangrove swamp) is an expanse of mangrove trees. These trees live near the shore in tropical marshes and tidal shores with their adventitious roots in the salt water..	MARGINS The margins of a leaf are its edges, which very from plant to plant. The margins can be smooth, serrated, or toothed; they can also be lobed or entire.
MASSARANDUBA TREE The Massaranduba tree (Manilkara bidentata)), also called the cow tree, macaranduba, bulletwood, and balata, is a large rainforest tree whose sap is milky white and is edible. Its fruit is also edible. This tree grows to about 100 to 150 feet tall and has a diameter of 2 to 6 feet. The tree's unusual bark is deeply-scored, reddish and ragged. The bark is used to produce a red dye. Many Massaranduba trees are in the rainforest are being harvested for its durable lumber.	MASS EXTINCTION Mass extinction is the process in which huge numbers of species die out suddenly. The dinosaurs (and many other species) went extinct during the K-T extinction, probably because of an asteroid that hit the Earth.	MEDULLARY RAYS Medullary rays (also called wood rays) are bundles of cells that radiate from the center of a tree like the spokes of a wheel (they are most easily seen in the cross section of a tree trunk). They store food and transport it horizontally within the tree.
MEIOSIS Meiosis is a process in which an eukaryotic cell's (diploid) nucleus divides twice and produces four daughter cells (called gametes or reproductive cells), each of which have half the genetic complement of the parent cell (they are haploid). This process was named by Farmer and Moore in 1905.	MERISTEM The meristem is a group of plant cells that can divide indefinitely. The meristem provides new cells for the plant.	MESIC Mesic environmental conditions are ones with medium moisture (water). Compare with very dry conditions (xeric) and very wet conditions (hydric).
MESIC SOIL Mesic soil is a medium type of soil (hence the name, which means middle) that drains well yet retains some water. Mesic soil is exellent for farming.	MESOPHYLL Mesophyll is the internal tissue of a photosynthetic leaf.	MESOPHYTE A mesophyte is a plant that has moderate water requirements. (Compare with hydrophytes and xerophytes.)
MESOZOIC ERA The Mesozoic Era ("The Age of Reptiles"), occurred from 248-65 million years ago. It is divided into the Triassic, Jurassic, and Cretaceous periods. Dinosaurs, mammals, and flowering plants evolved during the Mesozoic, and Pangaea broke up. The era ended with the K-T mass extinction.	METAMORPHIC ROCK Metamorphic rocks are compacted by pressure and heat from deep inside the earth.	METEOR A meteor is a meteoroid that has entered the Earth's atmosphere, usually making a fiery trail as it falls. It is sometimes called a shooting star. Most burn up before hitting the Earth.
METEORITE A meteorite is a meteor that has fallen to Earth. Meteorites are either stone, iron, or stony-iron.	METEOROID Meteoroids are tiny stones or pieces of metal that travel through space.	MICROPYLE The micropyle is the small pore in a seed that that allows water absorption.
MIDRIB The midrib (rachis) is the central rib of a leaf. It is usually continuous with the petiole and is often raised above the lamina (the leaf blade). On a compound leaf, the midrib extends from the first set of leaflets (where the petiole ends) to the end of the leaf.	MILANKOVITCH THEORY The Milankovitch Theory attempts to explain major temperatures changes on Earth, especially ice ages, by slight variations in the amount of sunlight reaching the Earth caused by the eccentricity of the Earth's orbit around the Sun. The Earth's orbital eccentricity changes the Earth's average distance from the sun and therefore slightly changes the amount of sunlight reaching the Earth. Milankovitch looked over the past 600,000 years and correlated summer temperature mimnima with four major ice ages in this time. Eccentricity cycles last over 100,000 years. This theory was proposed by Milutin Milankovitch in 1938. Recently, scientists (Richard A. Muller and Gordon J. MacDonald, July 11, 1997, Science) have found that changes in the axal tilt of the Earth's orbit more closely match glacial cycles for the past million years.	MILDEW Mildew is a parasitic, filamentous fungus that grows on a host plant.
MILKWEED Milkweed (genus Asclepius) is a common plant that contains toxins (poisons). There are more than 100 species of this perennial herb, containing varying concentrations of toxic chemicals (glycosides). Monarch butterflies (and other milkweed butterflies) lay their eggs on milkweed leaves; the caterpillars eat milkweed leaves to incorporate the milkweed toxins into their bodies in order to poison their predators.	MILKWEED BUTTERFLIES Milkweed butterflies are members of the family Danaidae. As larva, they eat the milkweed plant. Milkweed butterflies include the Monarch (Danaus plexippus), the Queen (Danaus gilippus), and others.	1,000,000 MILLION A million is a thousand thousand. The dinosaurs lived millions of years ago.
MINERAL A mineral is a naturally-occurring solid of definite chemical composition whose atoms usually form a regular pattern.	MITOCHONDRION Mitochondria (the plural of mitochondrion) are organelles within most eukaryotic cells - they power cells by generating energy (in the form of ATP, adenosine triphosphate) by breaking down glucose (a type of sugar). Mitochondria are self-replicating and bound by membranes.	MITOSIS Mitosis is a process in which an eukaryotic cell's nucleus divides after having duplicated its chromosomes - it produces two daughter cells that are genetically identical to the parent cell and to each other. Walter Flemming (1843-1905), discovered and named this process in 1870.
MIXED WOODLAND A mixed woodland is a woodland that has both conifers and broadleaf trees.	MOLD Mold is a type of fungus (and not a plant). Like other fungi, molds do not contain any chlorophyll (and cannot make their own food); molds live off the food produced by plants or animals, or decaying matter. Molds are often parasites on plants, animals, or even other fungi. Molds reproduce with spores. Some molds spoil our food, but other foods are produced by the action of mold (for example, blue, Roquefort, and Camembert chesses have mold growing in them, giving them their flavor). The anti-bacterial drug penicillin is made from the Penicillium mold (Alexander Fleming discovered penicillin in 1928). Classification: Kingdom Fungi, Division Eumycota (septate fungi), Classes Hyphomycetes, Oomycetes, and Zygomycetes.	MONERA Monera is a prokaryotic kingdom (separate from the plant kingdom) that includes the earliest forms of life on Earth, like archaebacteria (the oldest types of bacteria), eubacteria (like E. coli), and cyanobacteria (blue-green bacteria).
MONOCOT A monocot is a type of flowering plant (an angiosperm) whose seed has one embryonic leaf (cotyledon). The leaves of monocots generally have parallel venation (the veins are parallel to one another). The roots of monocots are usually fibrous and the flower parts are often in multiples of three.	MONOCULTURE Monoculture is a system of agriculture in which a single type of crop is grown in an area.	MONOECIOUS Monoecious plants have the male and female reproductive organs on the same plant. (Compare with dioecious.)
MONOPHYLETIC A monophyletic group consists of all organisms that share a particular common ancestor (and therefore have similar features). The members of a monophyletic group are more closely related to one other than they are to any organism outside the group. A monophyletic group is also called a clade. An example of a monophyletic group is mammals.	MONOPODIAL Monopodial (meaning "one foot") is a type of plant growth in which the plant has a single main stem. Compare with sympodial.	MORPHOLOGY Morphology is the study of the external structure of organisms (for example, the arrangement of leaves on a plant).
MORRISON FORMATION The Morrison Formation is a rock outcropping located in Utah, USA. This exposed sedimentary rock dates from the late Jurassic period, when this area was similar to a savanna (without the grass, since flowering plants hadn't evolved yet). Dinosaurs like Allosaurus, Seismosaurus, Ceratosaurus, Ornitholestes, and Diplodocus have been found at the Morrison foundation.	MOSS Moss is a small, low-growing, green plant that has a stem, leaves, and rhizomes (but no vascular system). Mosses reproduce with spores or by forming gametes. Classification: Kingdom Plantae (plants), Plylum Bryophyta (mosses), Four Classes: Class Sphagnopsida (Peat Mosses), Class Takakiopsida ("Takakiophytes"), Class Andreaeopsida (Granite Mosses), Class: Bryopsida or Musci ("True" Mosses). The true mosses (Class Bryopsida/Musci) are divided into three subclasses: Subclass Polytrichidae, Subclass Tetraphidae, Subclass Bryidae.	MUCIGEL Mucigel is a slimy, protective substance that is secreted by plant roots.
MULTICELLULAR Multicellular organisms consist of many cells. (Compare with unicellular.)	MUSHROOM Mushrooms are fast-growing fungi (they are not plants). They grow in dark, damp places and reproduce via spores.	MUTUALISM Mutualism is an association between two different species of organisms in which both benefit from the association. An example of mutualism is the relationship between bees and the flowers they sip nectar from- the bees get nectar from the flower and the flower gets pollinated by the bees. Mutualism used to be called symbiosis (which is now a more general term).
1,000,000 MYA "mya" stands for millions of years ago.	MYCORRHIZAE Mycorrhizae is a fungus that grows in a symbiotic relationship with the roots (or rhizoids) of a plant.

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Plants

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