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Ulcerative lymphangitis
A disease mainly of horses characterised by painful swelling of the lymphatics of the legs and ulceration.

Ultimate factors
In evolutionary terms the survival value of the adaptation in question; the evolutionary reason for the adaptation; opposite of proximate factors.

Ultra-centrifuge
A centrifuge with an extremely high rate of rotation which will separate out very small particles.

Ultra low volume (ULV)
Sprays applied as the undiluted formulation (see spray volumes). A spraying technique which utilises equipment delivering volumes below 5 l/ha with droplet size below 150 µm.

Ultraviolet (UV)
That portion of the light spectrum beyond the visible violet (to humans) but both visible and highly attractive to nocturnal insects.

Ultraviolet spectrophotometry
A technique in the identification of organic compounds by passing different wave lengths of the ultra-violet region of light through solutions in suitable solvents.

Umbilicus
The navel; the scar marking the point of attachment of the umbilical cord (the birth cord) in the foetus.

Unbiased estimator
An unbiased estimator Ø of a parameter Ø is an estimator for which the expected value of Ø is equal to Ø. That is E(Ø) = Ø.

Uncertainty
Conditions where there is no reliable data to help predict future events.

Undersize particles
Particles of a solid material smaller than an specified size.

Understory
Layer of plants near the ground.

Undulating membrane
Name given to two quite different structures in Protozoa; in some Mastigophora it is a fin-like ridge across the surface of a cell, with the axoneme of a flagellum near its surface; in some ciliates it is a line of cilia that are fused at their bases, usually beating to force food particles toward the gullet.

Undulating ridges
Undulatory waves in the surface of some protozoa, probably aided by sub-pellicular micro-tubules; the means of locomotion in some species.

Ungulate
Hoofed animal.

Unhulled seed
Ripe seed still retaining pods, glumes or other outer coverings.

Uniform probability distribution
A probability distribution having a constant probability over a finite interval from a to b, represented by f(x) = 1 a _ x _ b b - a

Uniramous appendage
An arthropod appendage that is unbranched, characteristic of living arthropods other than Crustacea, although some crustacean appendages are uniramous.

Unisexual
One sex.

Unit costs
A standard for costs per item, unit used for budgeting resources which have fairly stable costs, and which are used frequently by the research organisation.

Univoltine
Refers to an organism that has only one generation per year.

Unsulphonated residue
A measure of the saturated hydrocarbons in an oil that does not react or combine with sulphuric acid.

Update
The simulation process of changing the values of the state variables at each time step to reflect process rates at that time.

Uptake
The process of phytoplankton of actively absorbing nutrients from the surrounding water column.

Upwelling
The physical process in near-shore ocean systems of rising of nutrients and colder bottom waters to the surface because of constant wind patterns along the shoreline. Upwelling areas are highly productive of plankton and fish.

Urban
Peculiar to the human environment, as contrasted with that found normally in wild animals.

Urea
A non-protein nitrogen usually fed with molasses.

Uredinium
A lesion caused by a rust fungus, a group of spore-bearing filaments crowded together on which masses of urediniospores are formed.

Uredium
A fruiting body of the rust fungi in which uredospores are produced. A sorus in which urediospores are produced.

Uredospore
An asexual repeating spore of the rust fungi.

Urn
A region near the centre of the infusoriform larva of a dicyemid mesozoan.

Urosome
A portion of the body posterior to the major point of body flexion in many copepods; usually includes one or more free thoracic segments and abdomen.

Urstigmata
Sense organs between the coxae of the first and second pairs of legs on some mites, apparently humidity receptors; also called Claparedé organs.