Microgramma percussa (Cav.) Sota

This is a section of the rhizome of a fern, Pleopeltis percussa. To counter the fungal infection the cells produce lignin. Lignin makes the cell walls woody. With this strategy the plant tries to prevent the fungal infection to spread further.

Here, Acridin Red, a fluorescent stain, has been used to color the lignified cellwalls. You can see that the infected cells have an anomalous shape.