Critchfield, W. B. (1957). Geographic variation in Pinus Contorta. Harvard University.
Cita Chicago (17th ed.)Critchfield, William Burke. Geographic Variation in Pinus Contorta. Cambridge, Mass.: Harvard University, 1957.
Cita MLA (8th ed.)Critchfield, William Burke. Geographic Variation in Pinus Contorta. Harvard University, 1957.
Atenció: Aquestes cites poden no estar 100% correctes.