A last followup.

http://www.bioimages.org.uk/HTML/B147197.HTM

Hah!

If all of the books have been wrong about the size of P. involutus,
as Alick is quoted as saying, then that is the likely species. I shall
fiddle with ammonia, and see if I can manage to make my father's field
microscope work on the spores, but it was really only the size that
made me doubt P. involutus.


Regards,
Nick Maclaren.