Paulson, R. and Thompson, P. G. Reports on the Lichens of Epping Forest (First paper), Essex Naturalist, XVI. pp. 136-145, 1911; (Second paper), op. cit. XVII. pp. 90-105, 1913.
Peirce, G. J. Fixing and Imbedding Lichens. Journ. Applied Microscopy. Rochester, N.Y. I. pp. 99-100, 1898.
—— On the mode of dissemination and on the reticulations of Ramalina reticulata. Bot. Gaz XXV. pp. 404-417, 1898.
—— The Nature of the Association of Alga and Fungus in Lichens. Proc. Calif. Acad. Sci. Ser. 3, I. pp. 207-240 (1 pl.), 1899.
Peirce, G. J. The Relation of Fungus and Alga in Lichens. The American Naturalist, XXXIV. pp. 245-253, 1900.
Persoon, C. H. Einige Bemerkungen über die Flechten, etc. Usteri, Ann. Bot. VII. pp. 1-32, 1794.
—— Synopsis Methodica Fungorum. Göttingen, 1801.
Petch, T. The black termite of Ceylon. Ann. Roy. Bot. Gardens, Peradeniya, V. part 6, pp. 395-420, 1913.
Petiver, J. Musei Petiveriani. Cent. II. and III. London, 1695.