The medulla of a lichen is the loosely packed fungal layer.

Google

Structural Components of Lichen

https://openstax.org/details/books/microbiology/

Microbiology covers the scope and sequence requirements for a single-semester microbiology course for non-majors. The book presents the core concepts of microbiology with a focus on applications for careers in allied health. The pedagogical features of the text make the material interesting and accessible while maintaining the career-application focus and scientific rigor inherent in the subject matter. Microbiology’s art program enhances students’ understanding of concepts through clear and effective illustrations, diagrams, and photographs.

Microbiology is produced through a collaborative publishing agreement between OpenStax and the American Society for Microbiology Press. The book aligns with the curriculum guidelines of the American Society for Microbiology.

OpenStax Microbiology Textbook

The cortex of a lichen is the tightly packed fungal layer. 

Lichen Cortex

The thallus of a lichen represents its vegetative body, which is structurally organized into distinct zones: an outer, tightly packed fungal cortex; an inner algal zone; a loosely packed fungal medulla; a lower cortex; and root-like hyphal bundles called rhizines that attach the organism to its substrate.

Lichen Thallus

Lichen Medulla

The rhizines of lichen are the hyphal bundles used to attach to the substrate.

Learn Before

Related