Glossary for Gardeners – M

Glossary for Gardeners

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macronutrient
Collectively, the primary nutrients (nitrogen, phosphorus, and potassium) and secondary nutrients (sulfur, calcium, and magnesium) required for plant growth.
macropore
A large soil pore or opening. Macropores include earthworm and root channels, and control a soil’s permeability and aeration.
mandible
The first pair of jaws on insects. These are stout and tooth-like in chewing insects, needle- or sword-shaped in sucking insects, and the lateral (left and right) upper jaws of biting insects.
maturity
Ripeness, usually the state of development that results in maximum quality.
meiosis
A cell division process where the chromosome number is reduced by half.
meristem
Plant tissue in the process of formation; vegetative cells in a state of active division and growth, e.g., those at the apex of growing stems and roots.
mesophyll
A leaf’s inner tissue, located between the upper and lower epidermis, where raw materials (carbon dioxide and water vapor) are held for use in photosynthesis.
metabolism
The sum of the biochemical processes of a living cell.

metamorphosis
The process by which an insect develops. See complete metamorphosis, simple metamorphosis.
microclimate
The climate of a small area within a larger climate area. For example, a backyard can have a different microclimate from that of the surrounding neighborhood, or there may be different microclimates within a single backyard. Microclimates can significantly influence plant growth and should be considered in plant selection and care.
microfibril
A fine thread of cellulose in a cell wall.

micronutrient
A nutrient used by plants in small amounts, less than 1 part per million. Micronutrients include boron, chlorine, copper, iron, manganese, molybdenum, and zinc. Also called trace elements.
micropore
A fine soil pore, typically a fraction of a millimeter in diameter. Micropores are responsible for a soil’s ability to hold air and water.
middle lamella
A layer of pectin binding two adjacent cell walls.
mitochondria
Cellular bodies in which cellular respiration occurs.
mitosis
A cellular division process in which the chromosomes are duplicated.

modified central leader
A system of pruning used primarily on fruit trees. The tree’s central leader is encouraged for the first few years, then suppressed. This system allows for well-placed scaffolds and strong crotches, but keeps the tree’s crown relatively close to the ground for easy harvesting. Also called modified leader.

modified leader
See modified central leader.
molecule
A chemically bonded group of atoms.
molt
The shedding of an insect’s outer covering during growth. The form assumed between molts is called an instar.

monocot
A plant having one cotyledon (seed leaf). Also called monocotyledon.
monocotyledon
See monocot.

monoecious
A species having both male and female flowers on the same plant. Pecans, avocados, and squash are examples on monecious plants. See dioecious.
morphology
The study of the form of plants or plant parts.
mosaic
Nonuniform foliage coloration with more or less distinct intermingling of normal and abnormal colored patches.
mottle
An irregular pattern of light and dark areas.
mulch
Any material placed on the soil surface to conserve soil moisture, moderate soil temperature, and/or control weeds. Wood chips, bark, and shredded leaves are examples; inorganic materials such as rocks, plastics, or newspapers are also used.
multiple fruit
A cluster of mature ovaries from several flowers on a single stem.

mutation
A genetic change within an organism or its parts that changes its characteristics. Also called a bud sport or sport.
mycelia
Masses of fungal threads (hyphae) that make up the vegetative body of the fungus.
mycology
The study of fungi.
mycoplasma
See phytoplasma.
mycorrhizae
Beneficial fungi that infect plant roots and increase their ability to take up nutrients from the soil.