Glossary of Terms – ‘L’ WORDS
Word or Term
Definition
Labellum
The lower of the three petals of an orchid
flower, which differs in morphology and
patterning from the two lateral petals and
gives the flower its characteristic form.
Can also refer to the platform formed by the
lower petal or group of fused petals in various
other lipped flowers, such as those of the
Labiatae, Scrophulariaceae, and
Leguminosae.
A parenchymatous area in the stele of many
vascular plants, associated with and
positioned immediately above a leaf trace.
Leaf gaps are characteristic of angiosperms
but are also present in some gymnosperms
and ferns.
The ratio of the total surface area of a plant's
leaves to the ground area available to that
plant, i.e. LAI = leaf area/ground area. The
LAI is of value when considering the number
of plants that can be successfully cultivated
on a given area of land.
The evolutionary theory put forward by JeanBaptiste de Lamarck in 1809. He postulated
that a characteristic that is acquired during
the lifetime of an organism as a result of
environmental pressures can be transmitted
to the next generation. This is the theory of
the inheritance of *acquired characteristics”
and Lamarck believed that new species could
arise in this way. Erasmus Darwin also
supported this view, but Lamarck was the
first to give examples, one of which
concerned the seeds of marsh plants. He
suggested that if they reached high ground
they became adapted to drier conditions by
the development of new acquired
characteristics, which could be inherited by
the succeeding generation resulting in the
development of a new species. The theory
was later accepted by Darwin but challenged
by Weismann. Today Lamarckism has been
almost entirely rejected in favour of NeoDarwinism.
A layer within the cytoplasm or within an
organelle formed from a flattened membranebound vesicle or tubule. The vesicular cavity
is therefore narrowed so that the lamella
consists of two membranes lying close
together. Chloroplasts have a complex
Lacuna
LAI
(Leaf Area Index)
Lamarckism
Lamella
Also see.....
Lamina
Lanceolate
Landrace
Latent infection
Lateral root
Layering
LDP
(Long-day plant)
Leaching
internal system of lamellae.
The usually flattened blade-like portion of a
leaf, as distinct from the petiole and leaf
base. The shape of the lamina and the nature
of its margin are important taxonomic
character. Leaf laminas are usually the main
photosynthetic organs and are structured
accordingly. They are placed so as to make
the best use of incoming light with the
minimum amount of either overlapping or
wasted space. This is particularly evident in a
tree canopy. The pattern so achieved is
termed the leaf mosaic and is mainly a result
of phyllotaxis.
Narrow and tapering at both ends.
An ancient or primitive cultivar of a crop
plant. Landraces are often genetically very
heterogeneous and contain numerous alleles
that contributed to the survival of the
organism under natural conditions. Since
intensive plant breeding can result in the loss
of these alleles, landraces are a source from
which plant breeders can selectively
reintroduce them into highly bred cultivars.
An infection in which no symptoms are visible
during the first phase of the infection. Growth
of the pathogen stops soon after penetration
but resumes at some later stage
Any root that originates endogenously from
the pericycle of another root.
A method of plant propagation involving the
pegging down of runners and stolons to the
soil surface. Adventitious roots develop where
a node touches the soil and a shoot develops
from the lateral meristem. New daughter
plants eventually establish. Carnations are
commonly propagated in this way.
A plant that appears to require long days (i.e.
days with more than a certain minimum
length of daylight) before it will flower. In
actual fact, it requires a daily cycle with no
long dark periods.
The washing out of soluble substances from
the upper layers of the soil by water passing
down the soil profile. The substances are
either deposited lower down in the B horizon
or removed completely. It takes place when
the amount of rainfall exceeds the amount of
water lost by surface evaporation. It may
result in podsolization or the development of
an impermeable layer of mineral salts at
some point in the soil profile.
Leaf
Leaf buttress
Leaf culture
Lenticel
Ligulate
Limiting factor
Linear
Loam
Lobed
Loculicidal
Lomentum
The main photosynthetic organ of most green
plants, consisting of a lateral outgrowth from
a stem and comprising lamina , petiole , and
leaf base.
A lateral prominence on the shoot apex,
destined to differentiate into a leaf.
A form of tissue culture in which excised
leaves, leaf material, or leaf primordia are
grown on a sterile growth medium.
A small elliptical pore containing loosely
packed cells that is the means of gaseous
exchange in the *periderm of plant axes.
Lenticels are analogous to the stomata of
primary tissues and vary in size from being
almost microscopic to about 1 cm in length.
Strap or tongue shaped as, for example, the
outer ray florets of the inflorescences of
plants in the family Compositae.
A factor in the environment that by its
presence or absence, or increase or decrease
will govern the behaviour of an organism or a
metabolic process within an organism. Most
metabolic processes depend on more than
one factor being present in order to proceed.
When all other conditions are favourable, the
factor nearest its minimum value is the
limiting factor. For example, when a plant
photosynthesizes on a warm sunny day in a
moist environment, the amount of carbon
dioxide available in the air will be the limiting
factor. As evening approaches, light will
become the limiting factor.
Describing leaves, such as those of grasses,
that are elongated and parallel sided for
much of their length.
A type of soil in which there is an even
mixture of fine clay particles and coarser sand
particles. It is the best type of soil for
cultivation as the sand helps drainage and
aeration but the clay prevents excessive
water loss and binds the organic material.
Describing a leaf that is divided into curved or
rounded parts connected to each other by an
undivided central area.
Describing fruit dehiscence in which the slits
in the pericarp arise along the dorsal suture
of each carpel.
A dry dehiscent fruit, developed from a single
carpel, that contains one or more seeds. It
resembles a *legume but on ripening false
septa divide the pod into one-seeded units or
valves that fracture at maturity. Such fruits
Lumen
are seen in sainfoin (Onobrychis viciifolia).
A cavity enclosed by a cell wall, such as the
centre of a xylem vessel.