PLATE XL THE STRUCTURE OF WOOD. 



1. Cross section of six-year old stem of White Pine showing (b) bark, (c) cambium, (ar) annual 



ring, (p) pith, and (rp) numerous smail circular resin passages, natural size. 



2. A resin passage with bounding epithelial cells, enlarged. 



3. Non-porous wood of White Pine showing (spw) spring wood, (sw) summer wood, (ar) annual 



ring, and (rp) resin passage, x 3. 



4. Ring-porous wood of Chestnut, x 2. 



6. Ring-porous wood of Red Oak, showing large medullary rays, x 3. 



6. Diffuse-porous wood of Beech, x 4. 



7. Block of Chestnut wood showing (cs) cross section, (rs) radial section, (ts) tangential section, 



(spw) spring wood, and (sw) summer wood, natural size. 



