Barriers to decay in conifer roots

The process of compartmentalization, including the formation of barrier zones, localized discolored and decayed wood in roots of balsam fir, red spruce, eastern hemlock, white pine, and tamarack. The decay was caused by Armillaria mellea (Vahl. ex Fr.) Quel. and unidentified hymenomycetes. The most effective “walls” to decay were composed of resin ducts and parenchyma cells. Cylindrical patterns of decay formed due to tangential bands of resin ducts and parenchyma. In response to injury, conifer roots increase production of parenchyma cells which accumulate polyhenols. Three types of parenchyma may be produced: that associated with resin ducts, xylem rays, and tangential rings of cells resembling marginal parenchyma.