The anatomical structure of the secondary xylem (wood) of trees varies with location in the tree. The size, shape, and distribution of cell types varies not only between locations (i.e., stem vs. branch vs. root), but also within an annual ring or across annual rings at a given cross-sectional plane.
- secondary xylem,
- primary tissue,
- red oak
Available at: http://works.bepress.com/douglas_stokke/15/