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Bulbous growth in stem. It appears that whatever was in there has broken out. The end of the plant was dead beyond the gall.
Oak forest at Blue Sky Ecological Reserve
"Larvae cause tapered stem galls on black oaks (Quercus kelloggi, Q. agrifolia, and Q. wislizenii). As the larvae develop, the stem ruptures and eventually expels the larval capsules onto the ground. The linear fissures remaining on the stem become black, which distinguishes them from other black oak stem galls."