94 GENUS ABTEMISIA. 



Bessey's dicta, Mo. Bot. Gard. Annals 2:109, 1915), but if the sequence were reversed 

 it would run counter to these laws. Examples of this will be given a little farther on. 

 The subspecies ludoviciana is typically a form with small heads, the principal leaves with 

 a few short lobes, as shown in tracings from the type (fig. 8), and an evident but light 

 tomentum on the upper surface of the leaves, the lower surface heavily tomentose, as 

 in all the subspecies of A. vulgaris. The concept is here extended, however, to include 

 the more common form with the upper surface of the leaves nearly or quite glabrous; 

 also forms in which the leaves are variously lobed or entire, since these characters 

 have been demonstrated to be too subject to variation to be of taxonomic value. 

 Ludoviciana is a derivative of tilesi, and not the other way around, as seems evident 

 from its distribution and from the specialized nature of its characters, i. e. the reduced 

 heads, each with a reduced number of flowers, the narrower and simply lobed leaves, 

 and the tendency toward the development of a tomentum on the upper surface of the 

 leaves. 



A subspecies very close to ludoviciana, and united with it by Gray and others, is 

 gnaphalodes. This differs in having leaves which are heavily tomentose on both sides, 

 a character difference which ordinarily would not be considered as of much value, yet 

 one which is here found to be the most constant of all those proposed for the breaking 

 up of this complicated group of forms. Sometimes these two subspecies occupy adjacent 

 habitats. Subspecies ludoviciana then occupies the more shaded or moist situations, 

 the two forms thus standing somewhat in the relation of ecads to each other. At other 

 times, however, one will occupy vast extents of territory to the complete exclusion of the 

 other, as, for example, on much of the plains country east of the Rocky Mountains, 

 where in some districts only gnaphalodes is found. Just as ludoviciana may be looked 

 upon as a southeastern or Rocky Mountain development " from tilesi, so gnaphalodes 

 may be considered as the more xerophytic offshoot from ludoviciana, occupying in part 

 the same geographic area but also extending farther towards the east. Various forms 

 of leaves taken from plants growing on the same hillside are illustrated in figure 12. 



In the northerly part of the Mississippi Valley the gnaphalodes stock has so modified 

 the leaves that these have become elongated and drawn out at the apex into a more 

 or less tail-like appendage, while at the same time the heads remain larger than usual. 

 This is subspecies longifolia. It is easily recognized in its extreme development, but 

 frequent intergrades reveal its undoubted connection with gnaphalodes. The leaves 

 in longifolia are sometimes green on the upper surface. This is brought about by the 

 shedding in age of the heavy tomentum and hence does not indicate a direct connection 

 with ludoviciana. Various stages in this shedding process may be seen in specimens 

 collected at Lake De Smet, Wyoming {Nelson 8545, UC). 



The most striking of all of the subspecies of Artemisia vulgaris is serrata. This occurs 

 only in the upper part of the Mississippi Valley, where it grows in good and rather moist 

 soil. It is a larger plant than other subspecies of this region and bears much elongated 

 panicles of rather small heads (see table 6). The principal distinguishing characters, 

 however, lie in the leaves. These are remarkably constant in their lanceolate shape and 

 in the distribution of the pubescence, the upper surface being always green and nearly 

 or quite glabrous, the lower surface densely white-tomentose. The even serratures of 

 the margins also are usually constant, but a few collections exhibit intermediate forms 

 connecting with subspecies ludoviciana and gnaphalodes. Specimens referable to gnapha- 

 lodes, but with the leaves toothed somewhat as in serrata are: Spring Grove, Minnesota, 

 Rosendahl 693 (Gr), and near Minneapolis, Minnesota, 1892, Aiton (Gr). Leaves 

 with margins intermediate between these two subspecies are illustrated in figure 13. 

 The shape of the leaf is sometimes exactly matched in plants identified as subspecies 



