6 PREFAOE. 
is under especial obligations to Prof. B. L. Robinson, of the Gray 
Herbarium, for kindly counsel, as well as for much aid in the genus 
Lupinus; to Mr. Frederick V. Coville, of the National Herbarium, 
for his continuous helpful advice; to Dr. N. L. Britton, of the 
New York Botanical Garden, Mr. Stewardson Brown, of the Acad- 
emy of Sciences of Philadelphia, and Dr. C. F. Millspaugh, of the 
Field Columbian Museum, for the privileges of consulting the her- 
baria of which they have charge; to Mr. M. L. Fernald, of the Gray 
Herbarium, for technical assistance in various genera; to Dr. J. M. 
Greenman, of the Field Columbian Museum, for aid in Senecio; to 
Mr. A. A. Eaton, for a key to the species of Isoetes; to Mr. P. L. 
Ricker and Mr. W. F. Wight, of the Department of Agriculture, 
for assistance in bibliography; to Dr. Theodor Holm and Prof. C. F. 
Wheeler for aid in the genus Carex. 
Thanks are extended to the many persons who have favored Pro- 
fessor Piper with their collections of Washington plants, especially 
Mr. Kirk Whited, of Wenache, Washington; Prof. R. M. Horner, of 
Waitsburg, Washington; Prof. J. B. Flett, of Tacoma, Washington, 
and Mr. M. W. Gorman, of Portland, Oregon. 
For the privilege of examining their private herbaria Professor 
Piper is indebted to Mr. Thomas Howell, of Milwaukee, Oregon; to 
Mr. W. N. Suksdorf, of Bingen, Washington, and to Prof. L. F. Hen- 
derson, of Moscow, Idaho. 
Freperick V. CoviItie, 
Curator of the United States National Herbarium. 
