I have trouble figuring out what these structures are within the roots of Cerastium semidecandrum. I am working on a project that aims to determine the differences in (arbuscular) mycorrhizal fungi colonization of roots in lime-rich and lime poor coastal dunes. For most plant species it is clear whether the roots have mycorrhizal structures or not, however in most plants of Cerastium semidecandrum, I find these round black (stained) structures. These structures are mostly clustered and only visible in a few roots of the plant, there are no hyphea visible and thus I doubt the structures could be vesicles. The photo's are taken at 120X magnification (stereo microscope LEICA M165c). Roots were stained in a 5% ink-vinegar solution, black Pelikan ink and 4% acidified household vinegar was used, procedure according Vierheilig et al. (1998). I am absolutely no expert in this field, so I hope someone can help me out.