Pieters A. J.
The Plants of Lake St. Clair. Bull. Mich. Fish Com. 1894.
Pound, R., & Clements, F. E.
The Phytogeography of Nebraska. 1898. 2d ed. 1900.
A Method of Determining the Abundance of Secondary Species. Minn. Bot. Studies, 2:19. 1898.
The Vegetation Regions of the Prairie Province. Bot. Gaz., 25:381. 1898.
Ramond, L. F. E.
Voyages au Mont-Perdu et dans la partie adjacente des Haut-Pyrénées. 1801.
Raunkiar, C.
Vesterhavets Ost- og Sydkysts Vegetation. Bot. Cent., 41:361. 1889.