581.52072
Clausen, Jens Christian, 1891-
Experimental studes on the nature of
species [by] Jens Clausen, David D. Keck
[and] William M. Hiesey. Washington,
Carnegie Institution of Washington 1940-
t. ilus. 25 cm. (Carnegie Institution 
of Washington. Publication no. 520,
564, 581, 615)