102 GENUS ARTEMISIA. 



Although no practical value attaches to this plant, it is of economic interest because 

 of its abundance as a weed in certain districts, especially in the Mississippi Valley from 

 about the latitude of Missouri northward. Here it often completely occupies fallow 

 fields and other waste places, reproducing abundantly from seed. It is easily held in 

 check by cultivation or even by cutting, if the tops are destroyed before the seed ripens, 

 but the cutting must extend over at least two seasons since the root is often of biennial 

 duration. 



Artemisia biennis is objectionable also because of its pollen, which, as determined by 

 actual tests, is one of the causes of hay-fever in late summer and autumn. The pollen 

 is spherical, spiculate, and produced in great abundance. Its use in pollen therapy is 

 recommended for those patients who give a positive reaction to it in skin-tests. 



13. ARTEMISIA ANNUA Linnaeus, Sp. PI. 847, 1753. Plate 10. Annual Sagewort. 



An annual herb from a taproot, 3 to 30 dm. high, very sweet-scented; stem simple 

 below, erect or weak and fiexuous, striate, glabrous, rarely tinged with red ; basal leaves 

 crowded, petioled, 3 to 10 cm. long, once or twice pinnately parted or divided into lan- 

 ceolate pinnatifid segments, glabrous; upper leaves very similar; inflorescence a wide 

 and loose terminal panicle, leafy throughout, 10 to 50 cm. long, 3 to 20 cm. broad, the 

 very slender branches (racemes) widely spreading or recurved; heads heterogamous, 

 peduncled, not crowded, often nodding; involucre hemispheric, 1 to 1.5 mm. high, 

 slightly broader; bracts 8 to 14, the outer ones narrow and green, the inner ones broader 

 and scarious except along the green midrib, all glabrous ; ray-flowers 5 to 9, fertile, corolla 

 oblique, about 0.6 mm. long, granular; disk-flowers 5 to 20, probably fertile, corolla 

 broadly cylindric, about 1 mm. long, toothed, granular; style-branches flat, truncate; 

 achenes narrowly turbinate, apparently not nerved, glabrous. 



Native of Asia, where widely distributed, except in the extreme south, and of eastern 

 Europe, naturalized throughout the central and eastern part of the United States, to a 

 limited extent in the West, and in eastern Canada. Type locality, Siberia. Collections: 

 Charlottetown, Prince Edward Island, Fernald 8236 (Gr) ; Kingston, Ontario, September 

 13, 1900, Fowler (Gr, US) ; Bridgeport, Connecticut, July 9, 1895, Eames (US); Campbell 

 County, Virginia, Fauntleroy 621 (US); Cooke County, Tennessee, Kearney 793 (NY, 

 US); Ralls County, Missouri, September 13, 1913, Davis (SF); Benton County, Arkansas, 

 Plank (NY); Canton, northern New York, Phelps 1768 (Gr, US); Riverton, Nebraska, 

 Bates 4752 (Gr); Los Angeles, California, 1908, Arnold (Gr). 



RELATIONSHIPS. 



This is one of three species of the section Abrotanum that form a close group or sub- 

 section, the other two being biennis and klotzschiana. They are all annuals or at the 

 most biennials with a straight taproot and a terminal inflorescence, which begins well 

 toward the base of the strict, erect stem. However, some doubt as to the close relation- 

 ship between annua and the other two was introduced by J. D. Hooker who, in his Flora 

 of British India, reported as follows (Fl. Brit. Ind. 3:323, 1881): "Though usually 

 placed in the section Abrotanum, I find the ray-flowers to be always fertile and the disk- 

 flowers sterile." In that work annua was transferred to the section Dracunculus. 

 While the material now available is too young to permit of a definite statement as to the 

 fertiUty of the disk-flowers, the achenes are well formed, and both these and the corollas 

 are almost exactly like those of A. biennis at the same stage of development, except that 

 they are somewhat smaller. In any event, the two are so close in all other essentials 

 that their distribution into different sections seems scarcely advisable. The probable 

 origin from A. biennis has been discussed under that species. 



