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Xenia
The immediate visual effect of pollen on the endosperm due to the phenomenon of double fertilisation in the seed plants.

Xenic cultivation
The rearing of one or more individuals of one species in association with an unknown number of species of other organisms.

Xenobiotic
A chemical which is not a natural component of the living organism exposed to it.

Xenobiotic metabolism
The chemical transformation of compounds foreign to an organism by various enzymes present in that organism

Xenodiagnosis
Diagnosis of a disease caused by infecting a test animal.

Xenograft
Graft of a piece of tissue or organ from one individual to another of a different species.

Xenoma (also, xenom)
Xenoma tumour; a symbiotic complex formed by hypertrophying host cells and multiplying intra-cellular parasites, eg. certain micro-sporidians.

Xeric
Deficient in available moisture for the support of life (eg. desert environment).

Xerophile
An organism which can grow at very low moisture levels.

Xerophyte
Plant that can grow in dry places (eg. cacti). A plant structurally adapted for growth with a limited water supply.

Xiphidiocercaria
Cercaria with a stylet in the anterior rim of its oral sucker.

Xylem
The principal mineral and water-conducting tissues in vascular plants characterised by the pressure of tracheids. May also contain vessels, parenchyma cells, fibres and sclerids.