Fruiting bodies (ascocarps) of beech barkspot fungus, Diatrype disciformis. These fruiting bodies were about 2 - 3mm across.
This is what they look like through the camera on my new stereo microscope (magnification about 8x):
I used a razor blade to slice the top of one to reveal the perithecia:
And this is a vertical cross-section:
First photo and specimen taken in Chazey Wood, near Caversham, UK, on 2014-03-16.