28 THE PHYLOGENETIC METHOD IN TAXONOMY. 



changed, usually from that of variety to that of subspecies. In these instances the 

 carrying over of the author of the variety as the author also of the subspecies is con- 

 sidered not justifiable. 



An attempt has been made to give a complete synonymy under each of the species, 

 except when the synonym applies only to foreign variations, when its application to 

 North American forms can not be made with certainty, or when it results from such 

 remote transfers as that of Chrysothamnus from Aster. 



The citation of specimens examined is given for two principal purposes: (1) to indi- 

 cate the distribution, and (2) to enable workers at the various herbaria to gain a clear 

 notion of the authors' concepts of the species, subspecies, and minor variations. Speci- 

 mens fairly representative of the group under consideration and from different portions 

 of the area of distribution have therefore been chosen for citation, or if not representa- 

 tive, the variation is then indicated in parenthesis. A complete citation of all specimens 

 examined is given only when the group is rare or otherwise of special interest. Initials 

 and titles of collectors are seldom given, since it is believed that their omission will not 

 lead to confusion when looking up the specimens in herbaria. The names of certain 

 collectors have become so closely associated with botanical work in special regions that 

 their initials seem superfluous. When collections by another with the same surname 

 are cited, the initials of this latter botanist are given. Thus, "Jones" refers to Marcus 

 E. Jones, for plants gathered anywhere in the West, the few collections by W. W. 

 Jones being so cited; "Nelson" refers to Aven Nelson when Rocky Mountain plants are 

 indicated, but to "E. W. Nelson" in the case of Mexican specimens, collections by 

 Ehas Nelson being cited in full. 



The names of the herbaria in which the cited specimens were seen are indicated by 

 abbreviations in parenthesis following the name of the collector. The abbreviations 

 adopted are the following: 



CI, Unmounted specimens provisionally retained by the authors as part of the working collection of the Carnegie 

 Institution. 



DS, Dudley Herbarium of Stanford University. 



Gr, Gray Herbarium of Harvard University. 



NY, Herbarium of the New York Botanical Garden, including the Torrey and other herbaria of Columbia Uni- 

 versity, there on deposit. 



Phila, Herbarium of the Academy of Natural Sciences of Philadelphia. 



R, Rocky Mountain Herbarium of the University of Wyoming. 



SF, Herbarium of the California Academy of Sciences, San Francisco. 



UC, Herbarium of the University of California, including the Brandegee Herbarium. 



US, United States National Herbarium, including that of the United States Department of Agriculture. 



Herbaria studied and acknowledgments. — The detailed herbarium and statistical studies 

 necessary as supplementing the field work have been carried out for the most part at 

 the University of Cahfornia. Here every facility was freely available, including the use 

 of the herbarium and botanical library, and grateful acknowledgment is made to the 

 University authorities and especially to the Department of Botany. Other California 

 herbaria studied include those of the California Academy of Sciences, the Dudley 

 Herbarium of Stanford University, and the C. F. Baker Herbarium of Pomona College. 

 The Rocky Mountain Herbarium, at the University of Wyoming, was visited a number 

 of times and found to be extremely helpful, especially because of the large amount of 

 critical material brought together by President Aven Nelson and his staff. Professor 

 Marcus E. Jones, of Salt Lake City, courteously aided in the study of types and other 

 critical material in his collection, and the herbaria at the Universities of Nevada and 

 Arizona were frequently consulted. All of the material belonging to the three genera 

 here treated was examined by both authors in the winter of 1920-21 at three leading 

 herbaria on the Atlantic Coast, namely, the Gray Herbarium of Harvard University, 

 especially rich in types and in specimens gathered on the early surveys and expeditions 



