Horticulture Principles and Practices

Systemic pesticide A pesticide absorbed into a plant,
killing the organisms that prey on it.
T
Tap root A single root that grows vertically into the
soil.
Taxonomy The science of identifying, naming, and
classifying plants.
Terminal bud A bud located at the tip of a stem.
Terrarium A transparent glass or plastic container that
retains high humidity; used for displaying and
growing plants indoors.
Tetraploid Having four sets of chromosomes per
nucleus.
Texture (plant) The visual impact of a plant due to the
size of its leaves.
Thatch A layer of grass clippings, stems, and roots
that accumulates between the surface of a turf and
the soil.
Thinning The pruning technique for shrubs in which
the oldest stems are removed to stimulate new
growth; the selective removal of the excess fruits on
a fruit tree to improve the size and quality of the
remaining fruits. The term is also applied to the
removal of excess seedlings from a row of dense
planting for optimum growth.
Topdressing A method of fertilizer application that
involves the sprinkling of fertilizer over the soil
surface.
Topiary The formal training and pruning of a plant to
grow in a controlled shape.
Topsoil The upper layer of soil moved in cultivation.
Topworking (top-grafting) To change the cultivar of
a tree by grafting the main scaffold branches.
Trace element A micronutrient.
Translocation The movement of carbohydrates, water,
minerals, and other materials within the vascular
system of a plant.
Transpiration The loss of water from a plant, usually
through leaves, in vapor form.
Tuber A thickened underground stem in which
carbohydrates are stored.
Tunicate bulb A bulb that has a dry membranous
outer scale.
Turgor pressure The pressure within the cell resulting
from the absorption of water into the vacuole and the
imbibition of water by the protoplasm.
V
Variegation The genetic patterning of leaves with
white or yellow markings.
Variety (botanical) A subdivision of a species with
distinct morphological characters and given a Latin
name according to the rules of the International
Code of Botanical Nomenclature. A taxonomic
variety is known by the first validly published name
applied to it so that nomenclature tends to be stable.
Vascular cambium A meristem that produces
secondary xylem and secondary phloem cells.
Vascular cambium is found in biennials and
perennials.
Vector A carrier; for example, an insect that carries
pathogenic organisms from plant to plant.
Vegetative Referring to asexual (stem, leaf, root)
development in plants in contrast to sexual (flower,
seed) development.
Vernalization The practice of subjecting a plant to
cool temperatures for the promotion or enhancement
of growth or flowering.
W
Water table The upper surface of groundwater or that
level below which the soil is saturated with water.
Wavelength The distance between two corresponding
points on any two consecutive waves.
Weathering All physical and chemical changes
produced in rocks, at or near the earth’s surface, by
atmospheric agents.
Wilting point (permanent wilting point) The
moisture content of soil at which plants wilt and fail
to recover even when placed in a humid atmosphere.
Windbreak A planting of trees or shrubs, usually
perpendicular or nearly so to the principal wind
direction, to protect soil, crops, homesteads, roads,
and so on, against the effects of winds.
Wood Secondary nonfunctioning xylem in a perennial
shrub or tree.
X
Xanthophyll Yellow carotenoid pigment found along
with chlorophyll in green plants.
Xylem The portion of a plant vascular system in which
water and minerals, taken in by the roots, move
throughout the plant.
Z
Zygote A protoplast resulting from the fusion of
gametes (either isogametes or heterogametes).
754 Glossary