Critchfield, W. B. (1957). Geographic variation in Pinus Contorta. Harvard University.
Lua i Stíl Chicago (17ú heag.)Critchfield, William Burke. Geographic Variation in Pinus Contorta. Cambridge, Mass.: Harvard University, 1957.
Lua MLA (8ú heag.)Critchfield, William Burke. Geographic Variation in Pinus Contorta. Harvard University, 1957.
Rabhadh: Seans nach mbeach na luanna seo go hiomlán cruinn i ngach uile chás.