Stem pitting and annual ring discoloration in yellow birch

Abstract

The stem tissues of yellow birch (Betula alleghaniensis Britton) saplings, with wavy bands of stained xylem parallel to the annual rings and depressions in the xylem at the xylem–phloem interface (stem pitting), were studied microscopically. The bands of stained xylem consisted of abnormally formed parenchyma (parenchymatous wood) interspersed with collapsed cells. Rays in the affected areas showed increases in both cell numbers and cell size, often being indistinguishable from adjacent parenchymatous wood. Aggregate rays were associated with stained bands as well as with stem pitting in the xylem and corresponding protrusions of the phloem.