Elmer: What does it mean when a description says that a mushroom has "sterile gill edges" I have seen it in the description of Gymnopilus and in the description of one particular Mycena
Sava A gill edge is called sterile when it is covered with a
band of cells that are not basidia.
Those cells are called cheilocystidia. In some mushrooms,
there are no cheilocystidia at all; in some others,
they are interspersed with basidia on the gill edge;
and in some others yet, there are no basidia at all, only cheilocystidia.
In this last case, we say "sterile edge".
Note that on the gill faces one can always see basidia (mature or not). Sometimes, not always, on gill faces one can also see some other, usually larger cells that are not basidia (do not bear spores). Those are called pleurocystidia.
Hope this clarifies things a bit.
Elmer: Can one see a "sterile edge" with the naked eye?
Can one see is with a manual eye piece?
Sava: I don't believe you can recognize a sterile edge with the naked eye.
Sometimes, perhaps, you could see it with a 10x magnifier. I usually look for it first by placing the gill on a glass slide (no liquid mount nor cover glass) and looking at it though the 4x objective (which is 40x magnification). Sometimes those cystidia are tightly packed and not protruding, so to see them, you do need to use some mount and press down the cover glass to spread out the material.
You don't want to press too hard to get a "crush mount" because then the structure of the gill edge (or even its position) may be difficult to see.