DIAGNOSIS. 45 



peculiar habitats. In these, experiment alone can determine whether their stability- 

 is germinal or due to constant environic relations. 



In reviewing these lists it will be noted that the mobile species are not confined to 

 any one section, but that they are well distributed throughout the genus. It is apparent 

 that in each section one or two species have assumed the lead and by reason of their 

 high plasticity have been able so to accommodate themselves to a wide variety of 

 environmental impacts that related species have been largely excluded from extensive 

 areas. Whether favorable initial conditions have led to greater variation in some 

 species than in others, or whether the difference in the number of forms produced by 

 various species is due to an inherent difference in their plasticity, is an interesting 

 problem that scarcely falls within the scope of the present paper. 



GENERIC DIAGNOSIS. 

 ARTEMISIA Linnaeus, Sp. PI. 845, 1753. 



Annual and perennial herbs and shrubs, usually aromatic and bitter. Roots fibrous, 

 the annual species with a taproot, the perennial herbs often with rootstocks or caudex. 

 Leaves alternate, entire to variously lobed or dissected. Heads small, nodding or 

 erect, commonly panicled but the panicle sometimes much reduced and then raceme- 

 like, spike-like or globoid, apparently discoid but the marginal flowers with irregular 

 corollas except in one section where the flowers have been suppressed. Involucre ovoid to 

 campanulate or hemispheric; bracts imbricated in 2 to 4 series, dry, at least the inner 

 ones scarious or with scarious margins. Receptacle plane, convex or hemispheric, naked 

 or hairy or rarely chaffy. Ray-flowers pistillate and fertile or wanting; corollas narrowly 

 tubular, usually tapering upwards, with 2, 3, or 4 teeth, commonly oblique at orifice; 

 stamens wanting; style more or less exserted, 2-cleft, the branches terete to oblong and 

 somewhat flattened. Disk-flowers hermaphrodite, fertile or sterile; corollas campanu- 

 late, funnelform or trumpet-shaped, regular, 5-toothed; anthers longer than the fila- 

 ments, obtuse or subcordate at base, the connective produced into a lanceolate or subu- 

 late tip ; style exserted or sometimes included, cleft into 2 more or less recurved branches 

 which are flat, truncate, and erose or fimbriate at the end, or the branches more or less 

 fused into a slender column surmounted by an erose or fimbriate disk or cup. Achenes 

 in both ray and disk ellipsoid or obovoid to nearly prismatic, with 2 to 5 angles or ribs 

 or with numerous faint striae, or smooth, usually glabrous, rounded at summit to an 

 epigynous disk, or truncate, or crowned with a very short annulus. Pappus none. 



