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Formation of wound periderm appears to be a common form of resistance reaction in the Arceuthobium pusillum – Larix laricina combination, based on previous observations and an extensive examination of two witches' brooms of this host. Not only is wound periderm common in spur shoots within witches' brooms, but it also apparently restricts the development of the endophytic system in branchlets composing witches' brooms. Branchlets within witches' brooms of Pinus banksiana infected with A. pusillum and A. americanum also produced wound periderm similar to that described in eastern larch, which may account for the relative scarcity of aerial shoots on this host and restricted development of the endophytic system.
Tainter et al. (1971) studied this question.