30 iposteisia 



tribution of weeds, the plants met with 

 in the streets are nevertheless chiefly 

 mountain species. There are also some 

 few plants which have come up from 

 lower altitudes. A list of plants of 

 waste places made in late summer in 

 such a locality would include Physaria 

 didymocarpa, Gilia inconspicua, Achillea 

 lanulosa and various species of Rumex, 

 Polygonum, Potentilla, Artemisia, Aster, 

 Hordeum and Grindelia. The prickly 

 lettuce and shepherd's purse occur spar- 

 ingly. All of these plants are so few 

 and far between that one may almost 

 say that there are no weeds in high 

 altitudes. 



Plants of the Mesas. The mesas 

 are long, gently sloping, flat topped 

 ridges extending from the bases of the 

 foothills out towards the plains in an 

 easterly direction. They consist usually 

 of rock debris more or less decom- 



