To look at a symbiotic fungus inside a plant cell, scientists most of the time use electron microscopy. This interaction happening within one plant cell is so small that optical microscope are often not powerful enough.

This illustration was created from several references to show the fungus inside a living cell. I took inspiration from the 3D look and level of magnification that could be seen in an SEM, but I added organelles, which are absent in this kind of images.