Glossary for Gardeners – P

Glossary for Gardeners

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~ P ~

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 two 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 macronutrient, micronutrient.
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.