36 GENUS ARTEMISIA. 



The most primitive of the sections is Abrotanum. This seems certain from the con- 

 sideration that all others exhibit very marked peculiarities which could come about 

 only through the modification of an Abrotanum-Uke ancestor. Thus, forms without 

 ray-flowers or with aborted disk-flowers certainly were derived from a form in which 

 both ray-flowers and disk-flowers were present and fertile. The evident connection of 

 certain species of Abrotanum with the still more primitive Crossostephium is additional 

 evidence pointing in the same direction. Abrotanum is by far the largest of the sections 

 and is widely distributed in both the New and the Old World. The species are mostly 

 perennial herbs, the best known of which is the common mugwort, or sagewort {A. 

 vulgaris.) 



Absinthium is an assemblage of European and northern herbaceous perennials. It 

 differs from Abrotanum solely in the presence of a copious villous pubescence on the 

 receptacle. Since this character does not reappear elsewhere in the genus,' the group is 

 considered as a derivative or subdivision of Abrotanum which has not led to any decided 

 development. Its distinguishing character is not such as to warrant its recognition as a 

 separate section, yet it is continued because of usage and practicability. 



The two remaining sections of Artemisia have been evolved by the same process of 

 reduction as that exhibited in the development of the genus itself. The loss of the 

 pappus and of fully functional ray-flowers has been followed by the progressive reduction 

 of the flowers of the head. This appears to arise in consequence of the fact that the 

 ray-flowers and disk-flowers had come to have essentially the same function, and hence 

 to compete with one another for the food-supply brought to each head. A demand for 

 food in excess of the supply would inevitably bring about the reduction and loss of the 

 less important parts. This might operate in either of two directions, namely, to eliminate 

 the unnecessary pistils in the disk-flowers or to effect the loss of the ray-flowers, already 

 much reduced in functional value. Both of these specializations resulted in economy 

 of material and increase of parental care, and have actually been carried out in the 

 respective sections, Dracunculus and Seriphidium. 



The section Dracunculus, which comprises herbs and low shrubs of both hemispheres, 

 is here taken as a development from Abrotanum. It is considered as a farther advance, 

 for not only are the calyx-Umb and stamens of the marginal flowers wanting as in that 

 section, but the pistil of the central flowers ceases to function, so that the central achenes 

 are uniformly sterile and in most cases entirely aborted. There is thus a complete 

 division of labor between the two sorts of flowers, the marginal ones functioning exclu- 

 sively as pistillate, the others as staminate. 



Seriphidium is a comparatively small group in this country, where the representatives 

 are all shrubs or at least woody perennials, commonly known as sagebrush {A. tridentata, 

 etc.). In the Old World there are many herbaceous as well as shrubby species, but it 

 is not certain that these are of the same phylogenetic stock as the American ones. It 

 is possible that the characters of the section have been developed independently on the 

 two continents. If this is the case, then Seriphidium as now accepted is not a natural 

 subdivision. Whether of one origin or of two, this section, like Dracunculus, is probably 

 a derivative of Abrotanum, but its evolution has proceeded along quite different lines. 

 Instead of the central flowers becoming essentially staminate, they have remained 

 perfect and the achenes are fertile, but the marginal flowers have entirely disappeared, 

 thus rendering the head homogamous through reduction. This may be viewed as the 

 result of competition between the central and the marginal flowers of the head, the former 

 having succeeded in drawing food away from the latter, which in consequence have 

 failed to function and have finally disappeared from the heads. This is an advantage 



• The receptacle in A. cali/omica is Bometimes puberulent, but never long-hairy. 



