Hi,
I´ve got the answer at last !!
I am really pleased with myself this time!
It is the cleistothecium of a fungus in the genus
Phyllactinia.
This genus is pathogenic on tree leaves causing "powdery mildew".
The cleistothecium is a reproductive structure. It falls off the leaf and parachutes down using the appendages as a parachute. The fungus usually overwinters in this stage and then releases ascospores in Spring to infect the new opening leaves. The spores germinate producing hyphae which enter the leaf through the stomata.
See these websites for a bit more info:
http://en.wikipedia.org/wiki/Phyllactinia
http://botany.upol.cz/atlasy/system/gal ... %20fraxini
http://pnwfungi.org/featuredfungigallery.htm ....(see featured fungus #20)
I was way off track when trying to work out what it was with Franz´s specimen. The clue that got me thinking it was a fungus was what look like short hyphae in the first photo in this thread.
Ciao
Brian