Horticulture Principles and Practices

Herbaceous A plant that does not normally produce
woody growth.
Herbaceous cutting A cutting derived from
nonwoody plant parts.
Herbicide A chemical used to control weeds.
Heterosis The phenomenon whereby the hybrid of a
cross exhibits greater vigor and growth than either
parent (hybrid vigor).
Heterozygous Having different genes of a Mendelian
pair present in the same cell or organism.
Hill A group of seeds planted close together.
Horizon (soil) A layer of soil, approximately parallel
to the soil surface, with distinct characteristics
produced by soil forming processes.
Hormone (soil) A chemical substance that is produced
in one part of a plant and used in minute amounts to
induce a growth response in another part.
Horticulture The science and practice of growing,
processing, and marketing fruits, nuts, vegetables,
and ornamental plants.
Hot cap A paper or plastic dome set over warm-season
vegetables in early spring to protect them against
frost and wind and to increase the daytime growing
temperature.
Hotbed A bed of soil enclosed in a low glass or
transparent plastic frame and heated with electric
cables, steam pipes, or other heat sources.
Humidity The amount of moisture in the atmosphere.
Hybrid An offspring of two different varieties of one
plant that possesses certain characteristics of either
parent.
Hybridization The crossing of genetically dissimilar
individuals.
Hydroponics A method of growing plants using water
fortified with nutrients as the medium.
Hypogeous germination A type of seed germination
in which the cotyledon remains below the soil
surface.
I
Imbibition The absorption of liquids or vapors into
the ultramicroscopic spaces in materials.
Immune The state of being free from a given
pathogen, or not subject to the disease.
Incompatibility The condition in which two plants
will not cross-pollinate or a graft union is not
successful in spite of appropriate conditions.
Incomplete flower A flower that is missing one or
more of the following parts: sepals, petals, stamens,
or pistils.
Indehiscent fruit A fruit that does not split open
naturally at maturity.
Indeterminate A plant whose central stem or axis
grows indefinitely while flowers are continually
produced on lateral branches.
Inflorescence An axis bearing flowers, or a flower
cluster.
Insecticide Any chemical compound that kills insects.
Integrated pest management (IPM) A system of pest
control based on a good understanding of the life
cycle of the pest as well as cultural and biological
controls.
Internode The region of a stem between two
successive nodes.
Irrigation The deliberate application of water to the
soil.
J
Juvenility The first phase of plant development in
which growth is vegetative.
L
Lamina The blade or expanded part of a leaf.
Latewood (summer wood) The denser part of the
growth ring produced late in the season.
Layering A method of asexual propagation in which
roots are developed on the stem of a plant while it is
attached to the parent plant.
LD 50 The dose of a chemical at which 50 percent of
the exposed test population dies.
Leaching The washing out of the soil or medium of
soluble material with water.
Leaf apex The tip of a leaf.
Leaf base The section where the leaf blade joins the
petiole.
Leaf blade The flattened portion of a leaf that extends
from either side of the leaf stalk; also called lamina.
Leaf cutting A cutting made from a leaf and its
attached petiole used for propagation.
Leaf margin The edge of a leaf blade.
Leaflet One of the expanded, small leaflike parts of a
compound leaf.
Lean-to greenhouse A greenhouse that shares one
wall in common with a house or other building.
Light intensity The brightness of light.
Light reactions The reactions of photosynthesis in
which light energy is required.
Lignin An organic substance found in secondary cell
walls that gives stems strength and hardness.
Limbing up The removal of the lower branches of a tree.
Limestone A natural rock used to reduce soil acidity
or raise pH.
Loam A soil with approximately equal amounts of
sand, silt, and clay.
Lodging A condition in which plants are caused to
bend for various reasons at or near the soil surface
and fall more or less flat on the ground.
Long-day plant A species that flowers under
conditions of long duration of light and short daily
dark period.
750 Glossary