Xylem in galls of lodgepole pine caused by western gall rust, Endocronartium harknessii
Xylem in galls of lodgepole pine (P. contorta var. latifolia) caused by Endocronartium harknessii consists of unusually short, hyperplastic and hypoplastic aggregates of tracheids. The member pairs have random branching, shapes, and sizes. Some pairs and individual members or portions of them are atrophied in the early stage of differentiation. Others appear as strand tracheids. Ray crossings and coiled and reticulate patterns of aggregation in tracheids indicate that ray parenchyma fill multidirectional spaces and fan out spirally from a central point in the wood. The expanded rays consisting of isodiametric and cylindric ray parenchyma, and ray tracheids are connected to randomly spaced pit members at ray crossings that feature variable shapes and sizes of pit canals and chambers. The structure of the galls has many features in common with frost burls and frost ribs, i.e. chimeral nature, nodulations, abundance of rays, and hyperplastic and hypoplastic tissues.