Glass in thalli - from Ethel Mellor's doctoral thesis
These photos show cross sections of parts of the thalli of two lichens, each with embedded glass particles. In the photo on the left the letter "a" indicates a cluster of eroded glass particles. On the right the same letter is used to indicate two glass fragments. Mellor identified the lichens as Biatorina erysiboides (left) and Placodium murorum var. cinnabarinum (right).
Source: On the left is photo 25 and on the right is photo 26, both contained in plate 4 of Ethel Mellor's work: Les lichens vitricoles et la détérioration des vitraux d'église, Paris, 1921.