THE ADAPTATIONS OF THE PLANTS OF THE STEPPE 19 



(7) Destruction of exposed parts does not result in death of 

 the individual : 



In the case of many trees, shrubs and other plants belonging 

 to other ecological association, the individual is killed by the 

 destruction of the aerial parts. In the case of many steppe plants 

 such destruction is frequent by grazing animals and perhaps in 

 all bui: the season of greatest growth, by prairie fires. Certain 

 species are killed by too frequent fires (oftener than once in three 

 years for example) or by close pasturing, but the characteristic 

 steppe plants have wonderful resistance in this regard. 



(8) Ability to withstand inactivity (forced by drought) for 

 an entire season or even two or three years : 



This ability is very essential. After a series of wet years 

 many new immigrants into the steppe flora are noticed. The re- 

 turn of the dry cycle eliminates these species which are only 

 sojourners on the steppe. The characteristic species seem to be 

 uninjured by even prolonged drought. In the summer of 1911 

 for example, there were localities which for two years had been 

 so dry that no grass at all had started, yet when the unusual rains 

 of September came, even-thing was green in a few days. 



(9) Resistance to unseasonable weather: 



The vegetation does not readily start in the spring. However, 

 if after it has started a freeze comes, there is surprisingly slight 

 destruction of the characteristic plants. Early frosts in the fall 

 also affect the native steppe vegetation scarcely at all. 



(10) Marked seasonal succession depending on accumulated 

 temperature, water content of the soil, relative humidity, etc. : 



The succession of flowers, in an ordinary year is striking. 

 During one month the prairie is tinted by one group of flowers, 

 and during the next month by others, and the succeeding month 

 by still others. In this locality the early bloomers of the plains 

 include Cymopterus, Townsendia, Viola, Pulsatilla, Leucocrinum. 

 Among those blooming in June are Pentstemon, Allium, Zygode- 

 nus, Astragalus, Linum. In July, Braunia, Ratbida, Psoralea. 

 Malvastrum, Gaura, Euphorbia, etc., are prominent. During 

 August, the Asters, Solidagoes, Senicios, etc., are in their glory. 

 The Artemisias are in full bloom early in September. 



It has been determined by others that accompanying this 

 progressive activity there is a shifting in the floristic complexion 



