An unidentified white fungus growing inside a broken branch of an oak tree (Quercus sp).
The branch had recently fallen from the following tree:
The weakening caused by the fungus may have contributed to the branch breaking off.
I took the following specimen of the fungus home with me:
It yielded the following spores (magnification x600, field width 86um):
These are about 7 x 6.5um.
First two photos and specimen taken in the Wilderness, Whiteknights Park, Reading, UK, on 2014-03-02.