The medulla is the middle or lower layer of a stratified lichen that contains the mycobiont.
![](http://blogs.evergreen.edu/lichens/files/2011/03/torb_stratification_falsecolor1-300x225.jpg)
A false color scanning electron micrograph of Tuckermannopsis orbata showing the fungal medulla in purple and the cortex and photobiont in green. (A. Fischer 2/2011)