Decay caused by Armillaria mellea (Vahl. ex Fr.) Quel. and some unidentified hymenomycetes was localized in conifer roots. The processes of compartmentalization, including the formation of barrier zones, resulted in the localization of discolored and decayed wood in roots of 5 conifer species: balsam fir [Abies balsamea (L.) Mill.], red spruce (Picea rubens Sarg.), eastern hemlock (Tsuga canadensis (L.) Carr.], white pine (Pinus strobus L.) and tamarack [Larix laricina (Du Roi) Koch]. The most effective walls to decay were those composed of resin ducts and parenchyma cells and the best examples were seen in hemlock and balsam fir roots. 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 polyphenols. Three types of parenchyma may be produced: that associated with resin ducts, xylem rays and tangential rings of cells resembling marginal parenchyma. Parenchyma in tree roots should be considered in terms of storage and defense and compartmentalization of decay.
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