i9o8] HARVEY— PRAIRIE-GRASS FORMATION 291 



The prairie mugwort, Artemisia gnaphaloides, is gregarious upon 

 upper slopes. Here it forms dense patches, and these, on account 

 of the white tomentosity of its stems and leaves, which are frequently 

 ^Qcm high, are conspicuous in the dominant tone of yellow. It 

 bears to the autumnal quite the relation that the Antennarias hold to 

 the prevernai and vernal tone. Perennial from a tuber-like root, it 

 is also xerophytic in tendency. In its pappate achenes and root- 

 propagation are found the causes of its gregarious habit. 



The closing days of August are marked by the estivation of the 

 two false bonesets, Kuhnia eupatorioides and K. glutinosa. They 

 both occur but rarely and then mainly upon upper slopes and crests. 

 They form little clumps (several shoots from the same perennial 

 root) and are tall (50 to 75 '^'") and much branched, but on account 

 of their small few-flowered heads of creamy-white color and their only 

 occasional frequence, they never attain any prominence. However, 

 they become much more noticeable when the rich white pappus 

 spreads in maturation, during the second week of September. K. 

 eupatorioides is more mesophytic and so occurs more frequently over 

 the formation. K. glutinosa, however, is pronouncedly xerophytic, 

 and is restricted in its distribution to the open association along crests 

 and higher slopes. The abundant barbulate pappus assures proHfic 

 invasion, though establishment seems to be very limited, doubtless 

 due to the apparently low degree of adaptability possessed by these 

 forms. 



The Kuhnias are accompanied by Nabalus asper, which is 

 restricted to lower slopes, is of rare occurrence and thus always a 

 minor element. Though it is of the upper layer and bears numerous 

 heads of pale-yellow flowers, it blends into inconspicuousness in the 

 general tone. It is a perennial from a tuberous root. A well-devel- 

 oped parachute insures wide dissemination, but high ecological de- 

 mands preclude more than a rare establishment upon the prairie. 



The early days of September are well marked by the blooming of 

 four forms which occasionally attain more or less restricted promi- 

 nence: Aster sericeus, A. multijlonis, A. oblongifoliiis, and Kuhnistera 

 villosa. They are all of evident xerophytic tendencies and occur 

 mainly upon the upper slopes and crests. Appearing at a time when 

 there is an apparent decline in the dominance of the earlier tone, and 



