Looking at Felt's guide to american galls, there would seem to be way too many globular galls to narrow this down any.

If the galls were detachable and had no opening, I'd say the latter; if they were not detachable and had a small slitlike opening, I'd say the former. I can't tell from these photos.

Detachable meaning can fall off with very little pressure and without ripping a hole in the leaf? I'll start recording that info with next year's samples, and frass this one for now.

Thanks, I love winter b/c all my pics get second looks from folks that are not able to be out in the field.

It's not always easy to tell--detachable galls might rip a hole in the leaf if they're not yet "ripe," but when the larvae are mature the Caryomyia galls actually drop off the leaves. See the examples here. No one (including myself) has photographed what the opposite surface of the leaf looks like with Caryomyia galls, but here are some examples of what the openings look like on the larger Phylloxera galls (they're not this obvious on the smallest ones):

Of course, the most definitive way to tell is by looking at what's inside:

vs.

I'm going to move yours to the midge section. Now that I look again, there seem to be dimples in the upper right corner where a couple of galls have already fallen off. And it will be good to have your shot of the upper surface of the leaf for comparison purposes.