Stein-Carter, Jan. 1991. Ecology Lab Protocols                                     
     http://biology.clc.uc.edu/courses/bio303/protocol/

Nyle C. Brady, Emeritus Professor, Cornell University
Ray R. Weil, University of Maryland at College Park
2001

Richard H. Uva, Joseph C. Neal,  Joseph M. DiTomasco    
Weeds of the Northeast, 1999