white blood cell Component of the blood that functions in the
immune system. Also known as a leukocyte. wood The inner layer
of the stems of woody plants; composed of xylem. X-chromosome
One of the sex chromosomes. xerophytic leaves The leaves of
plants that grow under arid conditions with low levels of soil
and water. Usually characterized by water-conserving features
such as thick cuticle and sunken stomatal pits. x-ray
diffraction Technique utilized to study atomic structure of
crystalline substances by noting the patterns produced by x-rays
shot through the crystal. xylem Tissue in the vascular system of
plants that moves water and dissolved nutrients from the roots
to the leaves; composed of various cell types including
tracheids and vessel elements. Plant tissue type that conducts
water and nutrients from the roots to the leaves. zebroid A
hybrid animal that results from breeding zebras and horses. Z
lines Dense areas in myoÞbrils that mark the beginning of the
sarcomeres. The actin Þlaments of the sarc