26 THE PHYLOGENETIC METHOD IN TAXONOMY. 



The value of all quantitative studies depends upon the accuracy of the methods 

 employed. All measurements and counts tabulated in this paper were made either by 

 one of the authors or by a trained assistant. In the latter case a portion of the results 

 indicated for each form were carefully checked and all doubtful or extreme results were 

 either verified or eliminated. The examinations were carried out with the aid of binocular 

 dissecting microscopes equipped with micrometer disks ruled to 0. 1 mm. Larger measure- 

 ments, such as dimensions of the larger involucres, were made by using fine-pointed 

 calipers with a set-screw attachment. The dimensions are for material preserved in 

 liquid, or, when this was not available, for dried material which had been boiled after 

 the usual manner. It is believed that the only serious source of error is in the number 

 of disk-flowers reported for the Artemisias. In these plants the central flowers some- 

 times mature and drop out in the process of pressing. Therefore counts made from 

 herbarium specimens may be too low in some instances. Wherever this was suspected 

 the space in the table was left blank. The importance of boiling before taking measure- 

 ments of dried organs should be emphasized when a high degree of accuracy is desired. 

 In the Compositae the heads increase their diameter on pressing by as high as 25 per cent 

 in some cases and the flowers are sometimes appreciably shortened by drying and 

 wrinkling. The original shape and size are almost exactly regained by immersing in 

 boiling water for a few seconds. 



A series of experiments has been instituted for the purpose of testing the nature of 

 some of the criteria used in the classification of the genera here treated. Since the plants 

 are nearly all perennial, the results now available are limited. Transplants of Chryso- 

 thamnus have been carried from the desert area and established in coastal districts, 

 while others have been moved into different habitats in the Great Basin, with the result 

 that some definite information has been secured as to the constancy of certain forms. 

 Experiments in pruning and in the cutting of roots at different depths have supplied 

 data as to the ecologic behavior of this genus of plants. Reciprocal transplants of peren- 

 nial Artemisias in Colorado have demonstrated the constancy of such characters as 

 amount of pubescence for a period of three years in some cases, but it is still too early 

 to predict final results. Some of the annual Atriplexes have been grown at Berkeley, 

 where they could be kept under observation, with the result that certain characters of 

 young plants, particularly leaf position, have been found to be so different from those 

 described by earlier students of the genus that fundamental changes in the classification 

 have been necessary. The final results of the experimental studies will be reported 

 subsequently. 



Illustrations. — All of the accepted species and many of the subspecies and minor forms 

 are illustrated in the plates which accompany this memoir. This is entirely the work of 

 Miss Ruth Jeannette Powell, to whom the authors are under lasting obligations for the 

 exercise of much patience as well as artistic ability. Extensive scientific training has 

 given her an insight into the methods and aims of botanical research which has greatly 

 added to the accuracy of the results and to the clearness of their expression. 



A majority of the plates were prepared from fresh specimens sent directly from the 

 field. When it was found necessary to resort to dried or herbarium material, this was 

 first restored to its natural form by immersing in boiling water for a few seconds, or at 

 least a small portion was so treated to secure a correct idea of the size, shape, and relative 

 position of the various parts. In some Artemisias the difference between fresh and dried 

 heads amounts to as much as 10 per cent, but this varies with the amount of shrinking 

 and wrinkhng. All drawings made from dry specimens are indicated in the explanations 

 accompanying the plates, and all such were prepared from boiled material. The amount 

 of enlargement or reduction of each drawing is also indicated. It will be noted that 

 this has been kept constant for each structure throughout a genus, thus enabling one 



