24 THE PHYLOGENETIC METIIOD IN TAXONOMY. 



tion. As a consequence, they constitute indicators of great value, especially with refer- 

 ence to alkaline soils. Economically, the chief importance of Artemisia and Atriplex 

 is as browse plants, while Chrysothamnus is interesting as a source of native rubber. 

 All three genera have yielded a large number of segregates, and hence afford a good 

 test of the phylogenetic method in taxonomy and of its value in actual use. Conse- 

 quently, while the treatment has been made as thorough and consistent as possible, 

 much thought has been given to rendering the results of the greatest usefulness to the 

 non-speciaUst, ranging from the botanist and forester at one end to the physician and 

 plant-lover at the other. 



Field work. — As already indicated, taxonomic studies can be prosecuted to the best 

 advantage in places where the plants grow under natural conditions. It is only by this 

 means that a sufficiently large number of individuals can be passed in review, their varia- 

 tions noted, and the proper correlations made with environmental conditions. Other 

 methods have certain advantages ; for example, garden cultures permit of the assembUng 

 of forms for comparison and experimentation, but the time is past when any considerable 

 number of North American or European plants should be described as new or opinions 

 ventured as to their proper classification without a first-hand knowledge of their behavior 

 in the field. The value of careful studies in garden and herbarium should not be mini- 

 mized. In the case of a few rare species no other method is at present available, but the 

 comparatively small number of specimens that can be assembled even in the largest 

 establishments renders the results of such work necessarily incomplete. It seems, 

 therefore, that greater efforts should be made by taxonomists to carry more of their 

 work into the field and that much better facilities should be provided for such investi- 

 gations. 



With this importance of direct field studies in mind, much time has been given to them 

 in the preparation of the present monographs. A general ecologic and taxonomic interest 

 in the genera here treated had resulted in the assembling of a considerable number of 

 data before intensive work was begun. The earliest field trip with these groups espe- 

 cially in mind was in 1917. In August of that year, Hall made collections and studies 

 of Chrysothamnus in Colorado, Wyoming, and Nevada and spent the remaining months 

 of the year largely upon this genus, about six weeks being given to field studies in eastern 

 California and Nevada. These were continued in January and February of 1918, 

 during which months much distributional and ecologic information was obtained in 

 the desert area. In May, 1918, Clements prosecuted field studies on all three genera 

 as they occur between Tucson, Arizona, and Berkeley, California, and was joined by 

 Hall in June for similar investigations on a motor trip extending into Oregon and thence 

 to Colorado. In the late summer, Clements worked south to Texas and west to Arizona, 

 while Hall studied in western Colorado, Utah, and Nevada. The latter also visited 

 eastern California, and in December worked from Reno, Nevada, to San Diego, the 

 interest centering chiefly on Chrysothamnus. General field studies were combined with 

 experimental activities in Mono County, California. Some of the results, especially 

 those bearing upon the possibilities of this genus as a source of rubber and a classification 

 of the forms of C. nauseosus, together with data secured in Utah by M. E. Jones and in 

 Oregon, California, and Nevada by E. C. McCarty and J. R. Bruff, have been published 

 by Hall and Goodspeed (1919). 



The summer of 1919 was again spent by both authors at the Alpine Laboratory on 

 Pike's Peak, Colorado, and collections were made from adjacent districts. At the close 

 of the summer's work, field studies were prosecuted in unison during an automobile 

 trip from the Laboratory to Wyoming and across Utah and Idaho to Oregon and Cali- 

 fornia, Clements continuing the work to Tucson, Arizona. In 1920, Clements worked 

 along a different route between Tucson and Berkeley and made a trip from Arizona to 



