—— Pterigraphia Americana (Gazophylacium, Vol. II.). London, 1712.
Pfaff, C. H. Ueber eine neue eigenthümliche Säure in dem isländischen Moose (Cetraria islandica). Schweigger Journ. Chem. Phys. XLVII. pp. 476-483, 1826. See Berzelius, Jahresb. VII. pp. 216-217, 1828.
Pfeffer, W. Die Oelkörper der Lebermoose. Flora, LVII. pp. 2-6, etc. (1 pl.), 1877.
Phillips, W. Lichens, their rate of Growth. Gard. Chron. n.s. IX. p. 624, 1878.
Plot, Robert. The Natural History of Staffordshire. Oxford, 1686.
Plowright, C. B. British Uredineae and Ustilagineae. London, 1889.
Plukenet, Leonard. Phytographia. London, 1691-1696.
Porta, Joh. Bapt. Phytognomonica ... octo libris contenta. Naples, 1588.
Porter, Lilian. Attachment Organs of corticolous Ramalinae. Proc. Roy. Irish Acad. XXXIV. pp. 17-32 (3 pls.), 1917.
—— On the attachment organs of some common Parmeliae. Proc. Roy. Irish Acad. XXXIV. pp. 205-211 (3 pls.), 1919.