APA (7th ed.) Citation

Clausen, J., Keck, D. D., & Hiesey, W. M. (1941). Regional differentiation in plant species ([Sonderdr.].).

Chicago Style (17th ed.) Citation

Clausen, Jens, David D. Keck, and William M. Hiesey. Regional Differentiation in Plant Species. [Sonderdr.]. 1941.

MLA (9th ed.) Citation

Clausen, Jens, et al. Regional Differentiation in Plant Species. [Sonderdr.]. 1941.