The fungal skin of lichens prevents water loss to the algae below via its dense compacted thread structure.

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"Others [lichens] develop minuscule branches and grow into dense curling thickets a few inches high. Their outer skin is formed by the compacted threads of the fungi and is sufficiently impermeable to prevent the loss of water from the partnership; beneath are the algal cells, kept moist and protected from harmful ultra-violet radiation by the fungal skin; and below them, in the centre of the structure, there is looser tissue, also provided by the fungus, where food and water is stored." (Attenborough 1995:216)

Book
The Private Life of PlantsBBC BooksAugust 21, 1995
David Attenborough

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