ORIGIN AND DEVELOPMENT OF THE SECTIONS. 



35 



scheme that aims at a representation of relationships. It will be readily seen, however, 

 that the four sections are not of equal rank, the third and fourth differing from each 

 other only by the absence or presence of hairs on the receptacle. This was noticed by 

 Gray, for in his Synoptical Flora we find Abrolanum and Absinthium united into what 

 is called Euartemisia, the other two sections of Besser being retained with the same 

 Umits as in the Prodromus. The logic of this reduction is sound, but for practical pur- 

 poses it seems better to retain Absinthium and Abrotanum as sections. 



Up to the present time students of Artemisia seem to have contented themselves 

 with its subdivision into more or less natural sections, but have not been much concerned 

 with the phyletic arrangement of these sections. In even the latest treatments the 

 section Dracunculus is still found at the beginning, although there is abundant evidence 

 that this is a more highly specialized type than Abrotanum, and that, with the possible 

 exception of Seriphidium, it is the most highly developed of all of the groups. A 

 considerable rearrangement is therefore necessary in order to bring the sequence into 

 harmony with well-established principles of phylogeny. The various groups, their 

 distinguishing characteristics, and their probable relationships are indicated in the 

 accompanying chart (fig. 1) and may be expressed in key form as follows: 



Heads heterogamous, the marginal flowers pistillate. 



Central flowers fertile, with normally developed achenes. 



Receptacle not hairy 1. Abrotanum. 



Receptacle long-hairy 2. Absinthium. 



Central flowers sterile, their achenes aborted 3. Dracunculus. 



Heads homogamous, the marginal flowers wanting 4. Seriphidium. 



Fto. 1. — Phylogenetio chart of the sections of Ariemitia. 



This arrangement is based on the assumption that Artemisia is derived from an ancestor 

 resembUng Chrysanthemum or Tanacetum, in which the ray-flowers are present and 

 pistillate and the disk-flowers perfect and fertile. In the genus Tanacetum section 

 Sphaeromeria there is an evident reduction in the ligule of the ray-flowers, proceeding 

 in some cases to its complete elimination, when the corolla closely approximates that of 

 Abrotanum in structure and shape. 



