42 GENUS ARTEMISIA. 



leaf are shown, all from plants growing in a small range of hills in California. Many inter- 

 mediate forms could also be shown. While field studies are necessary fully to comprehend 

 the extent of this variation, some attempts have been made to bring the evidence into 

 herbaria. Thus, for example, at the United States National Herbarium is a series of 13 

 sheets of a form of A. vulgaris, filed under A. atomifera Piper, showing gradations in 

 leaf from entire or merely 3-toothed to divided with 3 spreading lobes on each side, 

 these lobes separate nearly to the midrib (Piper 6466). A still more extensive series 

 has been collected near Spokane, Washington, by Miss Evelyn Moore. These are now 

 on file at the University of California under A. vulgaris candicans. 



An attempt has been made to correlate these leaf-forms with ecologic conditions, and 

 some success has resulted at least as regards leaf-area. Thus, wide leaves are most 

 frequent in the north and along the Pacific Coast, whereas narrower leaves and lobes 

 become more abundant as a species extends its range to the south and especially to the 

 arid and more strongly illuminated portions of the southwest. The leaves shown in 

 figure 12 (p. 95) suggest an edaphic effect of environment, since all were from the same 

 climatic area. It will be noted from the explanation that the broader and more deeply 

 cut leaves are from the better and moister soil, while the narrower, entire ones are from 

 stony arid slopes. Nature and extent of lobing can not always be correlated with environ- 

 mental conditions, as shown by the frequent occurrence of very unlike foliage on plants 

 growing under apparently identical conditions. Leaves hke those labeled c to / of figure 3 

 are found on plants growing side by side. Much experimental work will be necessary 

 before the significance of such variations will be understood. 



The illustrations thus far referred to are mostly of the polymorphous A. vulgaris, 

 but similar conditions are found in other species. Variations are illustrated to a limited 

 extent in the plates, particularly in those of A. tridentata, and additional examples are 

 shown in figures 21 and 22 (pp. 144, 145). 



Stipule-like appendages have been noted in a few of the species and are illustrated in 

 figure 10. These are in reality lobes which have become isolated from the body of the 

 leaf and taken up positions near the base of the petiole, as is evident from their lack of 

 constancy in number, position, and size. Sometimes they grade insensibly into the 

 more conspicuous lobes of the blade. They supply a valuable character for the recog- 

 nition of A. procera, especially. As to A. vulgaris, they are almost uniformly present 

 in subspecies typica, very common but sometimes wanting in arctica, only occasionally 

 present in candicans and heterophylla, and almost entirely absent from the other American 

 subspecies. These facts are of much value as corroborative evidence in working out the 

 phylogeny of these forms. 



Stem and bark. — Among the herbaceous species it is found that certain minor characters 

 have been used to some extent as criteria. The reddening of the stems with age is very 

 noticeable in some cases and is at least a tendency which is helpful in the detection of 

 certain subspecies. The amount of pigment formed is known in other genera to be so 

 often dependent upon the amount of light that it is doubtful if the color is of more than 

 suggestive importance in Artemisia. The striation of the stem is quite marked in some 

 species, while others have smooth stems. This is again of minor significance, especially 

 as the striation is often masked by the pubescence. The character seems to be of some 

 value in distinguishing A. tridentata, in which the striae are present, but which often 

 requires the removal of the tomentum for their detection, from the very similar but 

 botanically distinct A. higelovi, in which the striations are entirely wanting. The 

 bark is different in different species, but it requires considerable field experience to make 

 use of this character. In cana, rigida, and pygmoea the bark is dark and fibrous. In 

 tridentata it is more shreddy and peels off in narrow strips, while in bigelovi it is sheathing 

 on the older parts of the stem and peels off in sheets rather than strips. 



