4 DISTRIBUTION AND MOVEMENTS OF DESERT PLANTS. 
in the necessity of accumulating and recording as extended a series of 
comparative observations as possible to serve as a basis for generalization. 
I wish to express my thanks to Prof. B. L. Robinson, of Harvard Uni- © 
versity; Messrs. F. V. Coville, of the U. 5. Department of Agriculture, 
and J. N. Rose, of the National Herbarium; Prof. H. M. Hall and Mr. 
T. S. Brandegee, of the University of California; and Prof. J. J. Thornber, 
of the University of Arizona, for free access to the herbaria under their 
charge, and for generous personal assistance at such times as it has been 
my privilege to consult them. I take pleasure also in acknowledging 
my indebtedness to Mr. S. B. Parish, of San Bernardino, who has kindly 
placed at my disposal numerous facts of local distribution, and to others, 
especially my colleagues of the Desert Laboratory, who in various ways 
have rendered substantial aid in the course of the work. 
