Glossary 219
Heterozygous: Having unlike alleles at corresponding loci of homologous chromo-
somes. An organism may be heterozygous for one or several genes.
High-pressure sprayer: A sprayer using a high-pressure pump to force the spray
through nozzles for both creating a fine spray and delivery to the plant.
Homozygous: Having genes at corresponding loci on homologous chromosomes
that are identical.
Honey dew: The sticky secretion produced by sucking insects such as aphids.
Humus: Organic matter rich in nutrients, brown or black in colour resulting from
partial decay of leaves and other matter.
Hybrid: The offspring of two plants of different species or varieties of plants. Hybrids
are created when the pollen from one kind of plant is used to pollinate an
entirely different variety, resulting in a new plant altogether.
IAA: Indole-3-acetic acid; used to promote rooting in cuttings.
Imperfect flower: A flower that lacks either stamens or pistils.
Inbred/inbreeding: An undesirable plant made by the crossing of two related
plants.
Incomplete flower: Flower that lacks any one or more of the floral parts, namely,
calyx, corolla, stamens and pistils.
Indeterminate: Said of those kinds of inflorescence whose terminal flowers open
last; hence the growth or elongation of the main axis is not arrested by the
opening of the first flowers.
Indicator plant: A sensitive plant that alerts to some conditions such as virus,
drought, and so on.
Infection: At the epidemiological level of the pathosystem, infection refers to
contact made between the host and the parasite known as auto-infection
and allo-infection. At the histological level, infection refers to the process
of penetration of a host by a pathogen.
Inorganic: Something that was never alive and manufactured by a human.
Inter-cropping: When two crops of different height, canopy, adaptation, root sys-
tem and growth habit are made to grow simultaneously in such a way that
they accommodate each other with least competition.
Inter-specific: Between species or hybrid cross.
Inter-stem/inter-stock: A piece of stem tissue grafted between a rootstock and a
scion.
Introduced: A plant that is exotic or brought from another region.
Isolation: The act of keeping the seed crops away from the sources of physical and
genetical contamination.
Isolation distance: The distance to be maintained between the seed crop and the
contaminant.
Juvenile: An early non-reproductive phase of plant growth, usually characterised by
different leaf shapes or by non-flowering and vigorous increase in size, and
often thorniness.
Larva: Immature insects such as caterpillars.
Layering: A method of vegetative propagation by which a branch of a plant is rooted
while still attached to the plant by securing it to the soil with a piece of wire
or other means.