176 IOWA ACADEMY OP SCIENCES. 



is particularly well adapted to xerophytic conditions, the 

 small teretish leaves make it admirably fitted for the con- 

 ditions existing upon the mounds. Along with it we find 

 the Pctalostono)! ntN/tifion/s, both belonging to the typical 

 plants of the plains of Nebraska and Colorado. 



Of the early composite flowering plants upon the loess 

 mounds the Echinacea anguf^fifolia and Rudbeckia hirta are 

 more or less common over the entire loess mounds. The 

 Hcliopsh scahra is common on the borders along with the 

 Sijiiijj/ioricarpus, Ceanothus and Verhcna. 



Solidago Missouriensis , Dysoides chtysaiithemoides , 



Achillea inilletohutn, Helianthus iMaxiiniLiani , 



Solidago rupestris , Grindclia squarrosa , 



Aster sericeus. Aster inuliiflorus , 



Antennaria planlagifiifolia, Ambrosia psilostachya , 



Stlene antirrhina, Helianthus rigidus, 



Asclepias verticillaia, Oxybaphus hirsutus, 



Oxybaphus angustifolius , Salvia lattceolata, 



Gerardia aspera, Gerardia tenuiflora, 



are some of the common types found over the entire loess 

 mounds. The Liatris punctata with its deep, straight roots 

 enables the plant to be adapted to the drouthy conditions 

 which frequently prevail in that region. The Yucca angus- 

 tifolia, common in sections of Nebraska, the Dakotas and 

 Kansas, is a rare plant in this region, although becoming 

 more common northward in the vicinity of Sioux City. 

 It is confined to the steep banks, well up near the summits 

 of the mounds. 



The mesophytic flora is gradually encroaching upon the 

 xerophytic, and as important forerunners for the meso- 

 phytic vegetation several of the shrubs like Syniphori- 

 catpos play a conspicuous part. Eastward in north- 

 eastern and central Iowa the Conjlns Americana is the chief 

 forerunner for the mesophytic flora. In the Missouri valley 

 the Si/rnphoricarpos is the chief factor in changing the char- 

 acter of the vegetation. 



The amount of precipitation collected for a series of 

 years indicates that this region is much drier than in the 

 drainage area east of the Missouri river basin. 



