Gardening Glossary

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P

The chemical symbol for phosphorus.

palisade mesophyll

The cells just beneath a leaf's upper epidermis that contain most of the leaf's chlorophyll and are responsible for most photosynthesis.

palmate

A form of espalier training.

palmate venation

A leaf whose veins radiate outward from a single point somewhat like the fingers of a hand.

palmately compound leaf

A leaf in which the leaflets radiate from one point.

panicle

A highly branched inflorescence.

parallel venation

A vein pattern in which the veins are parallel to each other.

parasite

Any animal or plant that lives in, or on, another animal or plant and withdraws nutrients from its host.

parasitic seed plant

A plant that lives parasitically on other seed plants. An example is mistletoe.

parenchyma

A thin-walled, undifferentiated cell.

parterre

A formal garden in which shrubs, flowers, and paths form a geometric pattern of matched pairs.

parthenocarpic

Development of fruit without fertilization.

pathogen

Any organism that causes disease. Generally applied to bacteria, viruses, fungi, nematodes, and parasitic plants.

pathology

The study of diseases.

pectin

A substance in cell walls binding cells together.

ped

A cluster of individual soil particles.

pedicel

The stem of an individual flower.

peduncle

The main stem supporting a cluster of flowers (as opposed to a pedicel, which is the stem of an individual flower).

pendulous

More or less hanging or declined.

perennial

A plant that lives 2 or more years and produces new foliage, flowers, and seeds each growing season.

perianth

Collectively, all external flower parts.

pericarp

The fruit wall; derived from the ovary wall.

pericycle

A root tissue giving rise to branch roots.

permeability

The rate at which water moves through the soil.

persistent

(1) Adhering to a position instead of falling, whether dead or alive, e.g., flowers or leaves. (2) A pesticide that retains its chemical properties in the environment for a long time.

petals

The usually showy structures around a flower's reproductive organs.

petiolate leaf

A leaf in which the blade is attached to a stem by a petiole.

petiole

The stalk of a leaf.

pH

A scale measuring the acidity or alkalinity of a sample. What the pH scale actually measures is the hydrogen ion (H⁺) concentration present. pH values run from 0 (the most acidic value possible) to 14 (the most alkaline value possible). pH values from 0 to 7 indicate acidity, a pH of 7 is considered to be neutral, while pH values from 7 to 14 indicate alkalinity. The scale is logarithmic, thus a difference of 1 pH unit is equal to a 10-fold change in acidity or alkalinity (depending on the direction), a difference of 2 pH units indicates a 100-fold change, and a difference of 3 pH units indicates a 1,000-fold change.

phenological stage

Crop development stage.

phenotype

The physical appearance of an organism.

pheromone

A vapor or liquid emitted by an insect that causes a specific response from a receiving insect. Some pheromones are used to attract a mate. Synthetic pheromones are used as attractants in insect traps.

phloem

Photosynthate-conducting tissue. See xylem.

phosphate

The form of phosphorous listed in most fertilizer analysis (P₂O₅).

phosphorous (P)

A primary plant nutrient, especially important for flower production. In fertilizer, usually expressed as phosphate (P₂O₅).

photoinduce

To initiate a physiological process as a result of being exposed to a specific photoperiod.

photoperiod

The amount of time a plant is exposed to light.

photosynthate

A food product (sugar or starch) created through photosynthesis.

photosynthesis

The process in green plants of using sunlight to convert water and carbon dioxide into sugar

phototropism

A growth response to light. Growth of a plant toward a light source is the most common example.

phytoplasma

A microscopic, bacteria-like organism that lacks a cell wall. Previously called mycoplasma.

phytotoxic

Toxic to a plant.

picotee

A pattern of flower petal coloration in which the edges of the petal are a contrasting color to the body.

pilose

Having long, soft hairs.

pinch

To remove a growing tip from a stem, thus causing axillary shoots or buds to develop. See deadhead, shear.

pinnately compound leaf

A leaf in which the leaflets are arranged on both sides of a common axis.

pinnate venation

A leaf vein pattern in which the major veins are arranged in rows on each side of the midrib.

pistil

The female sexual organ of a flowering plant, made up of the stigma, style, and ovary.

pit

A small opening in a cell wall.

pith

A region of parenchyma cells at the center of a stem.

plagiotrophic

Growth of a branch at an angle.

plant growth regulator

See growth regulator.

plant nutrition

A plant's need for and use of basic chemical elements. See macronutrients, micronutrients.

plasmolysis

Shrinkage of cytoplasm away from cell walls due to water loss.

pleach

To intertwine branches of a tree, vine, or shrub to form an arbor or hedge.

plena

A term used in botanical names to indicate a double-flowered variety. See double.

pleniflora

See plena.

pleno

See plena.

point source

A single, identifiable source of pollutants such as a factory or municipal sewage system. See nonpoint source.

pollard

A method of tree pruning that involves heading back severely to main branches each year so as to produce a thick, close growth of young branches.

pollen

A plant's male sex cells, which are held on the anther for transfer to a stigma by insects, wind, or some other mechanism.

pollenizer

A plant whose pollen sets fruit on another plant. See cross-pollination

pollination

The transfer of pollen from a male anther to a female stigma, enabling fruits to set and develop.

pollinator

An agent, such as an insect, that transfers pollen from a male anther to a female stigma.

polyploid

Having three or more sets of chromosomes per cell.

pome fruit

A fruit having a core, such as an apple, pear, or quince.

pomology

The science of fruits and the art of fruit cultivation, especially fruit trees.

postemergent

A product applied after crops or weeds emerge from the soil. See preemergent, preplant.

potash

The form of potassium listed in most fertilizer analysis (K₂O).

potassium (K)

A primary plant nutrient, especially important for developing strong roots and stems. In fertilizers, usually expressed as potash. See potash.

predator

An animal that eats another animal.

preemergent

A product applied before crops or weeds emerge from the soil. See postemergent, preplant.

preharvest interval

The period of time that must pass from the time a pesticide is applied to a crop until the crop is safe to pick and use.

preplant

A product applied before a crop is planted. See postemergent, preemergent.

prickle

A rigid, straight, or hooked outgrowth of bark or stems. Often called a thorn, but technically different. Roses are examples of plants with prickles. See thorn.

primary growth

Growth arising from cellular activities in apical meristems.

primary nutrient

A nutrient required by plants in a relatively large amount (nitrogen, phosphorus, and potassium). See macronutrient.

primocane

First-year growth, usually vegetative, on caneberries. Only fall-bearing raspberries produce fruit on primocanes late in summer.

processed fertilizer

A fertilizer that is manufactured or is refined from natural ingredients to be more concentrated and more available to plants.

prop root

A supportive root growing from an aboveground stem.

propagate

To start new plants by seeding, budding, grafting, dividing, etc.

protoplasm

The living substance of cells, including cytoplasm and nucleus.

prune

To remove plant parts to improve a plant's health, appearance, or productivity.

pseudobulb

A thickened, aboveground, modified stem that serves as a storage organ. Found in some orchids.

pubescent

Having short hairs.

pupa

The stage between larva and adult in insects that go through complete metamorphosis.