STATE OF ILLINOIS
DEPARTMENT OF REGISTRATION AND EDUCATION
H. H. ROSS
Printed by Authority of the State of Illinois
NATURAL HISTORY SURVEY DIVISION
George Sprugel, Jr., Chief
Circular 39 Urbana November, 1966
(Eighth Printing)
STATE OF ILLINOIS DEPARTMENT OF REGISTRATION AND EDUCATION
BOARD OF NATURAL RESOURCES AND CONSERVATION
John C. Watson, Chairman; Thomas Park, Ph.D., Biology; L. L. Sloss, Ph.D., Geology; Roger Adams, Ph.D., D.Sc., Chemistry; Robert H. Anderson, B.S.C.E., Engineering; Charles E. Olmsted, Ph.D., Forestry; W. L. Everitt, E.E., Ph.D., Representing the President of the University of Illinois; Delyte W. Morris, Ph.D., President of Southern Illinois University.
NATURAL HISTORY SURVEY DIVISION, Urbana, Illinois
SCIENTIFIC AND TECHNICAL STAFF
George Sprugel, Jr., Ph.D., Chief
Herbert H. Ross, Ph.D., Assistant Chief
Robert O. Watson, B.S., Assistant to the Chief