Erik,
This sounds very much like powdery mildew, a quite common plant disease
caused by an ascomycete fungus. The oval things then are the ascospores
of the fungus. They get air-borne and so manage to reach new hosts.
Best
-- Jan

Osiris wrote:
I found two plants in my garden with leaves that have white stuff on
them.
Under the microscope, it seems that the white stuff is actually asome
change of the leaf material...

Also under the scope I find very small, oval things. A lot of them.
They look like small eggs, only almost perfectly oval.
They seem translucent.
I held my digital camera against the ocular of the scope and produced
4 pictures. They are not very good, but they may give an impression.
magnification is 200x or 400x (don't know exactly anymore)

http://www.terwiel.com/diversen/DSCN0637.JPG (the white bubbles)
http://www.terwiel.com/diversen/DSCN0638.JPG
http://www.terwiel.com/diversen/DSCN0639.JPG (vague, in the center 2
bubbles)
http://www.terwiel.com/diversen/DSCN0640.JPG


I thought they may be louse/aphid eggs.

any suggestions ?

Erik