Fig. 21-22. Variants of 'wavy' bark in old S. atrocinerea: longitudinal depressions and lacunose (pitted) bark becoming fissured with age, on lower trunk (Houghton's Pond, Blue Hills Reservation, Milton, 22 August 2006).

Fig. 23. Old S. caprea with fissured bark (Joensuu, Finland, 17 May 2008) .

Fig. 24. A group of young S. caprea with smooth greenish-gray bark (Helsinki, Finland, 10 May 2008)

Fig. 25. A young branch of S. caprea (Helsinki, Finland, 10 May 2008)

Fig. 26. S. discolor (Boylston, central Massachusetts, 8 May 2008)

Fig. 27. S. discolor (Middlesex Fells Reservation, Winchester, 10 January 2009)

Fig. 28. S. bebbiana young bark (Aspen, Colorado, 3 August 2008)

Fig. 29. S. bebbiana older bark (West Boylston, central Massachusetts, 8 May 2008)

Fig. 30. S. bebbiana, old bark at trunk bottom (West Boylston, central Massachusetts, 8 May 2008)