NATIONAL ACADEMY PRESS
2101 Constitution Avenue, NW Washington, D.C. 20418
NOTICE: The project that is the subject of this report was approved by the Governing Board of the National Research Council, whose members are drawn from the councils of the National Academy of Sciences, the National Academy of Engineering, and the Institute of Medicine. The members of the committee responsible for the report were chosen for their special competences and with regard for appropriate balance.
This material is based upon work supported by the US Department of Agriculture, Cooperative State Research, Education, and Extension Service under agreement 97-COOP-2–5045. Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the authors and do not necessarily reflect the view of the organizations or agencies that provided support for this project.
Copyright 2000 by the National Academy of Sciences. All rights reserved.
Printed in the United States of America.