158 CLIMAX FORMATIONS OF WESTERN NORTH AMERICA. 



ones are regularly found in mixture, or as narrow band-like alternes. Arte- 

 misia cana has several times been met as a pure zone below A. tridentata, 

 but it is much more frequent in the mixed prairies. The tendency to form 

 pure stands of small extent is naturally more marked outside of the climax 

 area, since the other dominants of similar equivalence are usually lacking. 

 In spite of the major dominance shown by Artemisia tridentata, the associa- 

 tion is typically mixed in character. Of 406 instances, pure stands occurred 

 in but 75, while 331 were mixtures. Two and three dominants are the rule, 

 the former occurring in 142 cases, the latter in 139. Four dominants were 

 found in 44 localities, five in 5, and six in 1. The frequency of the most 

 important groupings is as follows : 



Artemisia tridentata-Atriplex confertifo- 

 lia, alone 24 



A. tridentata-A. confertifolia, with other 

 species 74 



A. tridentata-Chrysothamnus nauseosus or 

 C. viscidiflorus 31 



A. tridentata-Chrysothamnus, with others. 79 



A. tridentata-Grayia ± others 41 



A.tridentata-A. confertifolia, Grayia=t others 18 

 A. tridentata-A. confertifolia, Chrysothamnus 



± others 23 



A. tridentata-Gutierrezia ± others 30 



A. tridentata-A. canescens 28 



A. tridentata-Sarcobatus =*= others 23 



A. confertifolia-Grayia ± others, but no A. 



tridentata 10 



Correlations. — The dominants of the sagebrush association show the most 

 striking relation to the amount of salt in the soil. While they are essentially 

 xerophytes, the water relation is so obscured by the presence of salt that the 

 specific requirements and the successional sequence are most readily indicated 

 by the latter. Our knowledge of the salt relations of the dominants is due 

 chiefly to the work of Kearney, Briggs, Shantz, McLane, and Piemeisel 

 (1914), and of Shantz (Clements, 1916:237). The most saline of the species 

 considered here is the subclimax Sarcobatus vermiculatus with a mean of 0.8 

 per cent. Atriplex confertifolia possesses a mean of 0.5 per cent and Arte- 

 misia tridentata of 0.04 per cent. Grayia, Tetradymia, Atriplex canescens, and 

 Artemisia spinescens center about Atriplex confertifolia, while Chrysothamnus 

 nauseosus, C. viscidiflorus, Eurotia, Gutierrezia, and the several species of 

 Artemisia resemble the sagebrush more nearly. In spite of the excellent work 

 which has been done in the salt relations of the dominants of the sagebrush 

 association, these results do not suffice to explain their varied groupings, nor 

 are they in full harmony with what seems to be the successional sequence. 

 When two deep-rooted species, such as Artemisia tridentata and Sarcobatus 

 vermiculatus are found 23 times in intimate mixture, this relation does not 

 seem consistent with the mean salt-content for each. This discrepancy appears 

 even more striking in the case of Artemisia tridentata and Atriplex confertifolia, 

 which occur intimately associated in 98 localities. This relation is further 

 complicated by the fact that Artemisia tridentata not only occurs in 278 of the 

 338 mixed communities, but is also repeatedly associated with every one of 

 the saline dominants from Sarcobatus to Atriplex canescens. As a consequence, 

 it seems certain that we are not at the bottom of the salt relation. For a 

 complete understanding, it will be necessary to determine the root relations 

 of each dominant alone as well as in mixed stands, and to ascertain the 

 extremes of salt-content for it in the various mixed communities and at the 

 different working levels of the roots as well. Here, as everywhere else, the 

 behavior of the plant or community must be accepted as conclusive as to the 



