Xylem
The tissue of vascular plants that conducts water and minerals, provides support, and consists of tracheary elements and parenchyma cells. Woody tissue is made of secondary xylem produced by the vascular cambium.
Xenopus
Any of various aquatic, tongueless, clawed frogs of the genus Xenopus of southern Africa, certain species of which, especially the African clawed frog, are widely used for biological research.