Thanks, Zotto, 

I did search in the Pezizellaceae after observation of the prismatica type ectal , full of VBs ... 
but found no match 
Michel

Peut-être une idée stupide, mais pourquoi pas un champignon lichénisé ? Il me semble apercevoir sur les photos macros ce qui pourrait être un thalle...

perhaps what I suggest is ridiculous, but this fungus reminds me to some extent of Mniaecia, e.g. M. gloeocapsae s.l. - but I know those usually grow on soil. But perhaps the algae are more important?

Mniaecia so far never had VBs. it would surprize me.

Merci pour vos efforts, Nicolas, Zotto et Lothar.  

My first idea was also Mniaecia because of spore shape, but the other caracters do not fit, (VBs and négative IKI ) I also searched in other groups unsuccessfully. I also considered a lichen with no result  but I know too little about lichens. 

This collection was on a small piece of wood (most probably acer ) semi burried on calacareous soil. No thallus actually visible under lthe dissecting microscope and a croos section of tha apo is indeed difficult with a razor blade . 
I tried again anyway and one can guess  the hyalin medulla (prismatica-angularis) and also  some algae under the apo . These algae might be linked to the apos , I'm not sure, but I could not find such algae at the wood surface around the apos . 
See the (unfortunately poor quality) pics . 
Michel