Peltigera canina (Plate 72 from Albert Schneider's A text-book of general lichenology)
Explanation of the plate: 1. Whole lichen. 2 Section through apothecium. 3. Section through thallus. 4. Ascus and paraphysis. 5. Spores.
In figure 3 the circular area outlined in red indicates a soredium from another lichen that has landed on the surface of the Peltigera thallus. A soredium is a tiny vegetative propagule, consisting of some hyphae and photobiont cells and in this case the foreign soredium has been trapped by some of the short hyphae that project from the upper side of the Peltigera thallus.
Albert Schneider's A text-book of general lichenology, published in Binghamton in 1897 by Willard N. Clute & Co. illustrates the structural features of various lichens from the north-eastern United States.