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Xanthidium is a genus of minute unicellular algae of the desmids having a rounded shape and armed with glochidiate or branched aculei. Several species occur in ditches, and others are found fossilised in flint and hornstone.
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In botany, the term xanthocarpous refers to a plant which bears yellow coloured fruit.
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Xantholinus is a genus of rove beetles, Staphylinidae, characterised by a short, blunt, small frontal process on the large, long, wide head.
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In botany, the term xanthopous is applied to a plant which has a yellow stipe, or stem.
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In zoology, the term xenobiosis refers to a form of symbiosis that occurs among some ants in which two colonies of different species of ants live in the same nest, without rearing their broods in common.
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Xenoderminae is a subfamily of the family Colubridae, of reptiles of the suborder Serpentes (Snakes). The subfamily is comprised of about 12 species in seven genera native to south-east Asia and South and Central America where they live in humid areas, swamps and tropical rain forests.
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Xenopeltidae is the 'Sunbeam Snake' family of reptiles of the suborder Serpentes (snakes). The family is represented by a single genus.
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Xeris is a genus of Horntail (Siricidea). Xeris spectrum is a mostly black species with yellow spots on the sides of the prothorax, and partly yellowish-red legs. The female is armed with a long ovipositor, but is actually harmless to man, the ovipostor serving only for laying eggs. Xeris spectrum is distributed over most of Europe, Siberia, China and Japan and is between 15 and 30 mm long. They are mostly found in pine woods where the adults fly on warm, sunny days. The larvae feed on the cellulose of wood, taking between two and three years to develop, and are often introduced into buildings through timber.
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Xestobium is a genus of beetle of the family Anobiidae. The genus includes the Death-watch beetle (Xestobium rufovillosum).
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Xiaosaurus was a dinosaur of the Jurassic period. Only a few partial remains of Xiaosaurus have been found, and from these it is thought it was a herbivore, about one metre long, that walked on its hind legs and had short arms and was related to Fabrosaurus.
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In botany, the term xiphophyllous refers to a plant as having sword-shaped leaves.
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Xiphosura are the king-crabs order of Arachnida. They are aquatic animals with gill-books.
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Xiphydria is a genus of insects of the family Xiphydriidae. Xiphydria camelus is the most common member of the family Xiphydriidae, and is distinguished by the white stripes on its head. The larvae usually develop in alder trees, but in some places in birch trees.
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Xiphydriidae is a family of insects of the super-family Siricoidea, sub-order Symphyta, order Hymenoptera. The members have a conspicuously long neck.
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Xuanhanosaurus was a dinosaur of the Jurassic period. It is only poorly known from a few bones which indicate a dinosaur related to Allosaurus, from which one may infer Xuanhanosaurus was a carnivore, about six metres long, that walked on its hind legs.
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Xyeloidea is a super-family of insects of the sub-order Symphyta, order Hymenoptera. They are evolutionarily very old and have 12-segmented, unusually shaped antennae, the last nine segments being very short and weak.
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Xyleborus is a genus of beetle of the family Scolytidae that live in the wood of deciduous trees and have their brood galleries there. They don't eat the wood but rather the ambrosia fungoid that grows on it. The males are wingless and after mating die.
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Xylem is a woody tissue that transports water and dissolved mineral nutrients in vascular plants. In flowering plants it consists of hollow vessels (known as vessel elements) that are formed from cells joined end to end. The end walls of the vessel elements are perforated to allow the passage of water. In less advanced vascular plants, such as conifers and ferns, the constituent cells of the xylem are called tracheids. In young plants and at the shoot and root tips of older plants the xylem is formed by the apical meristems. In plants showing secondary growth this xylem is replaced in most of the plant by secondary xylem, formed by the vascular cambium. The walls of the xylem cells are thickened with lignin, the extent of this thickening being greatest in secondary xylem.
Xylem contributes greatly to the mechanical strength of the plant: wood is mostly made up of secondary xylem.
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Xyletinus is a genus of beetle of the family Anobiidae comprising ten species, one of which occurs in Britain. Both sexes have stout, distinctly serrate antennae of eleven segments. They develop in dry wood and bark on deciduous trees, some larvae also live in dung.
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In botany, the a xylocarp is a plant that bears fruit which has a hard or woody pericarp (such as a coconut for example).
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In botany, the term xylocarpous refers to a plant that bears fruit which becomes hard or woody (such as a coconut).
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Xylodromus is a genus of rove beetles, Staphylinidae, found in mouldy hay and straw.
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Xylopertha is a genus of small False Powder-post Beetles (Bostrychidae).
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Xylosteus is a genus of longhorn beetles (Cerambycidae). One species, Xylosteus spinolae is found in Europe where it develops in hazel wood, taking two years to develop into an adult.
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Xyloterus is a genus of beetle of the family Scolytidae that lives on felled timber, scraping passages in the timber and then eating the ambrosia fungi that grows on the walls.
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Xylotrechus is a genus of rare longhorn beetles (Cerambycidae) which run about on stacked timber.
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Xysticus is a genus of crab spider. Xysticus cristatus is a common and widespread British species with a body about six millimetres long found in hedgerows and meadows where it waits on twigs or flowers, motionless, for passing insect prey.
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