54 BOOT DEVELOPMENT IN THE GRASSLAND FORMATION. 



Seneca, Nebraska, where further studies were made, lies in the heart 

 of the main body of the Nebraska sandhills. Here the hills rise ab- 

 ruptly from the narrow flood plain of the Middle Loup River to a 

 height of about 200 feet. In the main they are well covered with grass 

 and freely dotted with shrubs and coarse herbs (plate 8). Blowouts in 

 all stages of development may be found. Here are to be seen Red- 

 fieldia flexuosa with Psoralea lanceolata, Cyperus schweinitzii, Pent- 

 stemon haydenii, and others colonizing areas of bare sand; mats of the 

 prickly-leaved Muhlenbergia pungens, or local areas dominated by 

 the coarse sand-reed, Calamovilfa longifolia. However, most of the 

 hillsides are well covered with many species of bunch-grasses, shrubs, 

 interstitial herbs, short-grasses, and sedges. Many of the latter exhibit 

 varying degrees of the bunch-grass tendency. Unlike conditions in the 

 true prairies and even in the better developed mixed prairies on harder 

 lands, the plant cover is open. Only in the most favored situations 

 on protected north slopes is the light-colored substratum hidden from 

 view, while normally bare intervals of sand are the rule. This pre- 

 vailed, although the area examined was ungrazed and, judging from 

 the amount of accumulated debris in the "pockets," had not been 

 burned over for a number of years. 



Andropogon scoparius, A. hallii, and Calamovilfa longifolia, with 

 Stipa comata, Koeleria cristata, and Panicum virgatum (in less exposed 

 places), are the dominants among the tall-grasses. Bouteloua hirsuta 

 and B. curtipendula with Carex pennsylvanica and C. stenophylla make 

 up the major portion of the lower layer of grasses and grass-like species. 

 Yucca glauca is fairly abundant. Ceanothus ovatus (including the 

 pubescent variety), Prunus besseyi, and well-developed clumps of 

 Rosa arkansana constitute the shrubby or half-shrubby species. The 

 sand-cherry is most abundant in the more open portions of the vege- 

 tative cover. Isolated bushes of Ceanothus occur throughout, even 

 dotting the crests of the hills, while Rosa arkansana makes its best 

 development in sheltered places. The open nature of the bunch- 

 grasses makes possible the presence of a great many subdominant 

 species. In the main they are similar to those described at Haigler, a 

 station 145 miles south and west (fig. 14). The most marked difference 

 aside from the better development of the grasses at this station is the 

 abundance of Artemisia filifolia in the former area and its almost com- 

 plete absence in the less compact soils of the rougher topographic region 

 about Seneca. At this station the following species were examined: 



Onagra biennis. — The common evening-primrose is a species of frequent 

 occurrence in both true and mixed prairies, where it forms societies. It is 

 most common in rather dry situations and where the vegetation is somewhat 

 open. It usually indicates disturbed conditions. 



A number of specimens of this primrose were excavated on a grassy hill- 

 side. The plants were in full bloom. In one root system the tap-root was 



