DESCRIPTION OE THE PLATES. 



xxvii 



10. Thelotrema lepadinum. 



11. Ditto, portion of thallus, magnified. 



12. Ditto, section of an apothecium. 



13. Urceolaria scruposa. 



14. Ditto, apothecia, magnified. 



15. Ditto, section of an apothecium. 



16. Ditto, spore. 



17. TJ. cinerea, portions of thallus, magnified, showing relative 

 positions of apothecia, a, and spermogones, b. 



18. Ditto, section of thallus, showing an apothecium, a, and 

 a spermogone, b. 



19. Ditto, section of a spermogone. 



20. Ditto, sterigmata and spermatia. 



21. Ditto, spore. 



22. Verrucaria alba, spores in different states of development. 



23. V. epipolcea, spore. 



24. V. plumbea, ditto. 



25. V. irrigua, ditto. 



