320 IOWA ACADEMY OF SCIENCE 



Oryzopsis hymenoides Elymus condensatus 



Sporobolus cryptandrus .Tuncus balticus 



Salsola kali tragus Grindelia nana 



Atriplex hastata Chrysothamnus viscidiflorus 



Lepidium medium Artemisia canadensis 



Gaura parviflora Artemisia ludoviciana 



Anogra pallida Artemisia tridentata 

 Verbena bracteosa 



The Oryzopsis is remarkably abundant. The Russian thistle 

 here attains its maximum size. The Chrysothamnus is extreme- 

 ly abundant and is quite generally distributed, while the sage- 

 brush, though covering a more limited area, grows in places 

 very rank. That such species as J uncus balticus and Gaura 

 parviflora- should appear in the same association as sagebrush 

 seems a little strange. The anomaly is perhaps owing to the 

 combination of sandy soil, hot, dry winds, and close proximity 

 to the river. The plants of this section suffer more, it would 

 seem, from the direct effects of the wind, than any others of 

 the region. Species with delicate foliage cannot survive here, 

 and low forms are likely to be buried by the drifting sand. 



The vegetation of the slope leading up to the higher land is 

 scant and mostly short, this being also much exposed to the 

 wind. Sagebrush is here almost wanting; there is an abund- 

 ance of very dwarf Chrysothamnus viscidiflorus, Achillea mille- 

 folium lauulosa, Amsinckia intermedia,, and Bromus tectorum, 

 while la rue areas are whitened over with PI an to go purshii. 

 Where there is an abundance of fine loose sand piled into low 

 dunes by the wind, there may be found here and there large 

 patches of Cleome lutea and Psoralea lanceolata scabra, and a 

 scattered growth of a peculiar dune grass, Elymus flaveseens. 



The elevated section, by far the most extensive in area, did 

 not yield a very long list of species. While the total of indi- 

 vidual plants is sufficiently large, nearly all of them are so 

 dwarfed as to form but a scant mantle of vegetation. Over 

 tracts many acres in extent one may scarcely find a plant of any 

 sort rising to a height of more than two feet. Another pecu- 

 liarity of the species of this region is their "mosaic" mode of 

 growth. One will come abruptly upon a certain form dis- 

 tributed in immense abundance over a considerable area of 

 land, but when this is crossed, the species leaves off as abruptly, 

 and perhaps another takes its place in equal profusion. Usual- 

 ly no particular reason for this phenomenon can be assigned. 

 At the time of our visit the spring vegetation of ephemeral an- 



