Acknowledgments 
It would be impossible to personally thank 
everyone who so generously helped Dr. Egolf 
and me in compiling this checklist, particu- 
larly during Dr. Egolfs long illness and upon 
his tragic death. However, I would like to 
express my sincere appreciation to the follow- 
ing people whose generosity enabled the 
completion of this work: Dr. Peter A. Hyypio, 
L.H. Bailey Hortorium, Ithaca, New York; Ir. F. 
Schneider, Institute for Horticultural Plant 
Breeding, Wageningen, Holland; and Dr. 
Elizabeth McClintock, California Academy of 
Sciences, San Francisco, California, who 
reviewed early versions of the checklist and 
provided much-needed information. 
Dr. Theodore Dudley, U.S. National Arbore- 
tum, Washington, DC; Dr. Arthur O. Tucker, 
Delaware State College, Dover, Delaware; 
Harry J. van de Laar, Boskoop, Holland; and 
Freek Vrugtman, Royal Botanical Gardens, 
Hamilton, Ontario, Canada, who provided in- 
depth reviews of the current checklist and 
offered invaluable suggestions. 
Mme. H. Bertrand-Breisch, Ecole Nationale 
Ingenieurs Travaux Horticulture et Paysage, 
Angers, France, and Dr. Alain Cadic, Institut 
National de la Recherche Agronomique, 
Beaucouze, France, who were particularly 
helpful in obtaining additional information on 
specific cultivars and in completing registra- 
tions. 
ANNE O. ANDRICK 
Washington, DC 
Abbreviations 
AAN American Association of Nurserymen 
Bros. Brothers 
OG degrees Celsius 
ca. circa 
cm centimeter, centimeters 
Co. Company 
CV. cultivar 
ed. edition, editor (pl., eds.) 
et al. et alia, and others 
f. forma 
OD degrees Farhenheit 
ft feet 
HCC Horticultural Colour Chart 
ibid. ibidem, in the same place 
Ltd. Limited 
m meter, meters 
mm millimeters 
NA U.S. National Arboretum, 
Washington, DC 
NA No. U.S. National Arboretum 
accession number 
No., no. number 
Nr. number 
page (pl., pp.) 
PI No. Plant Introduction accession number 
Pty. Proprietary 
® registered trademark 
rev. revised 
RHS Royal Horticultural Society, London, 
England; also designates the Royal 
Horticultural Society Colour Chart 
sp. species 
ube registered trademark 
var. varietas, or botanical variety 
vol. volume 
x multiplication sign signifying 
hybridity 
yd yard 
yr year, years 
zone USDA plant hardiness zone (U.S. 
Department of Agriculture 1960) 
= equal sign signifying synonymy 
ts uncertainty as to parentage or data 
[ ] enclose added information not in the 
source or enclose editorial comments 
