38 GENUS ARTEMISIA. 



Differences in shape and especially in size are often due merely to differences in 

 maturity. This is so evident, and fully ripe achenes are so seldom represented in herbaria 

 that a statement of size in a diagnosis is rarely of value. On the contrary, it is often 

 positively misleading. For these reasons the size is not indicated in the descriptions 

 in the present paper. 



Notwithstanding the considerable fluctuation within even a single species, achenial 

 characters serve somewhat as a guide in the matter of natural groupings. Thus, for 

 example, in the section Abrotanum the achenes are comparatively short and tend 

 toward the formation of a border or crown at the broad summit. This border fits 

 loosely around the base of the corolla-tube. It is most noticeable in A. pontica, A. 

 abrotanum, and A. calif ornica, all of which seem to be primitive in most of their other 

 characters. The crown-like summit is here perhaps a remnant of the disk which bore 

 the pappus in those forms precedent to Artemisia in the line of evolutionary develop- 

 ment. A similar but less definite crown persists also in section Seriphidium, but here 

 it is usually associated with more elongated achenes, often with four or five raised 

 longitudinal ribs or angles. 



Style-branches. — The usual condition of the style is 2-cleft at maturity, as in most 

 Compositae. In the ray-flowers the branches are either acute or thickened and somewhat 

 obtuse, while in the disk-flowers the branches are almost uniformly truncate at apex 

 and more or less distinctly fimbriate or at least penicillate. In some cases, however, 

 the style in the disk-flowers is undivided and capped by a disk with a roughened or 

 fimbriate border. This is certainly a development from the 2-cleft style, brought about 

 by the fusion of the branches. It obtains only in certain species of the section Dracun- 

 culus. This character of the peltate stigmas has sometimes been used for the purpose 

 of distinguishing the dracunculus-campestris group, in which the style is said to be undi- 

 vided, from the filifolia-pedatifida group, in which the style is described as usually more 

 or less 2-cleft. An examination of seven collections of A. dracunculus from widely sepa- 

 rated locaUties discloses the fact that in all of these the style is cleft into two lobes, 

 which are erect, or nearly so, as in A. filifolia. Frequently the branches stand so close 

 together that they appear to be united, yet when lightly pressed with a needle they 

 spring apart or even recurve. No instance of complete fusion was encountered in this 

 species, although the condition doubtless exists. Fusion is apparently more common 

 in A. campestris, 5 subspecies of which were studied, with 42 as the total number of 

 flowers examined. In 30 of these the style-branches were completely fused, while in 

 the remaining 12 they were separate at least along one margin. Completely fused 

 branches and fully cleft styles are frequently found in the same head: In some cases 

 the fusion is evident only along one side, the result being a cylinder split down for a 

 short distance along a single line. 



Passing to A. filifolia, it was found that both conditions always obtained on the same 

 plant as far as examined, a small majority of the styles having fused branches. A 

 similar condition prevails in A. pedatifida, and in this species the various degrees of 

 fusion are especially well represented (e. g., Nelson's 7058, from Sweetwater County, 

 Wyoming.) Two of the stages are shown on plate 16. In A. spinescens the branches 

 are always completely united, as far as has been observed. 



The fused character of the styles is thus seen to be a variable trait, occurring irregu- 

 larly in one section of the genus and hence of little specific and of no sectional or sub- 

 generic value. 



Corolla. — The size of the disk-corollas is sometimes of very definite value as a specific 

 and subspecific character. Certain species, notably A. parryi, A. stelleriana, A. pattersoni, 

 and A. pedatifida, stand off very sharply in this feature from their nearest allies. The 



