Horticulture Principles and Practices

Parent stock The plant from which material is
obtained for propagation.
Parthenocarpy The development of a fruit without
sexual fertilization.
Pathogen A disease-causing organism.
Peat Any unconsolidated soil mass of semicarbonized
vegetable tissue formed by partial decomposition in
water. An example is sphagnum peat moss.
Pedicel Individual flower stalk of an inflorescence.
Pedigree A record of ancestry.
Perennial A plant that grows year after year without
replanting.
Pericarp The fruit wall, which develops from the
ovary wall.
Perlite A coarse material made from expanded
volcanic rock.
Pesticide A chemical used to control undesirable
organisms (pests).
Petiole The stalk that attaches the lamina or leaf blade
to the stem.
pH A measure of the acidity or alkalinity of a medium
or liquid.
Phloem The portion of the vascular system in which
photosynthates are transported throughout the
plant.
Photoperiod The length of day.
Photoperiodism The response of plants to the relative
length of light and darkness.
Photosynthesis The chemical process by which green
plants manufacture food using carbon dioxide and
water in the presence of light.
Phototropism The hormone-induced bending of a
plant toward light.
Physiological disease A diseaselike symptom
produced by plants due to an improper or inadequate
supply of essential nutrients.
Phytochrome The chemical involved in plant response
to photoperiod.
Pinch pruning The removal of the terminal bud of a
plant to stimulate branching.
Pistil The female reproductive part of the flower,
consisting of the stigma, style, and ovary.
Plant breeding The science of controlled pollination
of plants to develop new cultivars.
Plastids The cellular organelles in which carbohydrate
metabolism is localized.
Plugging A method of lawn establishment whereby
small cores of sod are transplanted.
Pollarding A training method for deciduous trees
whereby branches are severely pruned to leave stubs
from which new shoots grow.
Pollen The male sex cells borne in the anthers of
flowering plants.
Pollination The deposition of pollen on the flower
stigma.
Polyploidy A condition in which a plant has somatic
(non-sexual) cells with more than 2n chromosomes
per nucleus.
Pome A simple fleshy fruit, the outer portion of which
is formed by floral parts that surround the ovary.
Pomology The science and practice of fruit culture.
Pore spaces The gaps between the particles of soil or
other growing media.
Postemergence herbicide An herbicide designed to
kill weeds after they become established.
Pot-bound A condition in which the roots of a plant
growing in a restrictive container environment grow
around the walls.
Potting mixture (soil mix) Combination of various
ingredients such as soil, peat, sand, perlite, or
vermiculite designed for starting seeds or growing
plants in containers.
Preemergence herbicide An herbicide designed to
kill weeds as they germinate.
Profile The vertical section of the soil showing
horizons or layers.
Propagation The reproduction or increase in the
number of plants by sexual or vegetative methods.
Pruning The removal of parts to control a plant’s
growth, size, or appearance.
Public area The part of a landscape in front of a house
and viewable from the street.
Pure line A population of plants descended from a
single homozygous individual.
R
Raphe Ridge on seeds, formed by the stalk of the
ovule, in those seeds in which the funiculus is
sharply bent at the base of the ovule.
Recessive The condition of a gene such that it does not
express itself in the presence of the contrasting
(dominant) gene.
Recombination The mixing of genotypes that results
from sexual reproduction.
Registered seed The progeny of foundation or
registered seed produced and handled so as to
maintain satisfactory genetic identity and purity, and
approved and certified by an official certifying
agency. Registered seed is normally grown for the
production of certified seed.
Relative humidity The amount of water vapor present
in the air compared to the total amount the air could
hold at its present temperature.
Resistance The capacity of a plant to resist disease or
insect attack.
Respiration The breakdown of carbohydrates to yield
energy for use by the cell.
Rhizome The underground stem that grows
horizontally and produces roots on the lower surface
while producing shoots above the ground.
752 Glossary