A. TRIDENTATA, 



145 



in any large herbarium, has been constructed from specimens in the herbarium of the 

 University of California as follows: 



(1) Typica, near Empire, Colorado, Patterson 219 (UC 29790). 



(2) Reduced size without other change, west of Hosier, Wyoming, September 10, 1919, Clements (UC). Minor 



variation 15. 



(3) Same as 2, but with reduced upper leaves, south of Laramie, Wyoming, September 9, 1919, Hall (UC). 



(4) Same as 2, but with narrow inflorescence. Mono County, California, August 18, 1898, Congdon (UC). 



Minor variation 11. 



(5) Same as 4, but with green involucres, Laramie, Wyoming, Nelson S1S5 (UC, 146504). Genuine nova. 



In the subspecies trifida the narrow inflorescence is combined with a foliage more 

 deeply cleft than in either typica or nova. This tendency toward cleft or parted leaves 

 is common also in other subspecies, that is, it combines promiscuously with other char- 

 acters. It is especially frequent in arbuscula {Heller 12914, from Placer County, Cali- 

 fornia, etc.), highly developed in some specimens of spiciformis {Nelson 8941a, from 

 Albany County, Wyoming, etc.), and a form of the latter has been named A. spiciformis 

 longiloba (Osterhout, Muhlenbergia 4:69, 1908). Although the character has been 



FiQ. 22. 

 Artemisia tridentata trifida, A. t. bolanderi, 

 and A. carta: a, b, c, all from the aame plant, re- 

 ferred to trifida but perhaps a hybrid between this 

 and cana (Lima, Montana, Hall 11569); d, from 

 A. t. bolanderi (Mono County, California, Clements 

 and Hall 11702); e, an unusual form of cana from 

 Wyoming (Hall 10992), listed as minor 

 All X 1. 



accepted as of specific value in the case of trifida, it is usually passed over as a trivial 

 variation when it occurs in these. In the present paper it is used as a character to aid 

 in the recognition of a variety of long standing in the literature, marked also by its narrow 

 inflorescence and an indescribable thyme-like aspect of the leafy twigs. It should be 

 emphasized, however, that not all of the sagebrushes with trifid leaves belong to the 

 subspecies trifida. 



The next two subspecies, that is, arbuscula and rothrocki, differ from the four already 

 discussed in having usually larger heads. The difference is not so great, however, as 

 the measurements given in descriptions would seem to indicate, for specimens are fre- 

 quently found which, although plainly of this group, have heads scarcely larger than in 

 the other subspecies. The size of the involucre is associated with the number of flowers 

 which it incloses, and this is evidently a more definite criterion for general use. From 

 table 14 it will be seen that the number of flowers in the subspecies thus far discussed 

 is 3 to 6, rarely 7, 8, or 9, while in these two the number runs from 6 to 13 and even to 20 

 in erratic plants, and is only rarely as low as 4 or 5. While there is thus a notable tend- 

 ency in opposite directions, the overlapping is sufficient to indicate that the two groups 

 of subspecies are not specifically distinct. 



The subspecies arbuscula is apparently more primitive than rothrocki, or at least it 

 presents less evidence of being a highly modified form. It is a low, straggling shrub with 

 numerous rigid branches and is especially suited to the rigorous environment in which it 

 grows. Its popular name of scabland sagebrush is indicative of the unfavorable soil and 

 moisture conditions with which it must contend. It seems almost certain that it is a 

 derivative of typica developed under the unfavorable conditions so common to the 



