FERN FLORA OF NEBRASKA 313 



from the wooded bluffs into favorable situations. The trees are of 

 the broad leaf species except in the northwest where there is a de- 

 velopment of the yellow pine. 



In Nebraska the fern flora reaches its greatest development in 

 this region. The principal fern species of this region are Bot rye Il- 

 ium virginianitm, Adiantuui pcdatum, and Filix fragilis. In the 

 crevices of the rock clifts, often more or less exposed, are found : 

 Cryptogranuitc acrosticJioides (rarely), N otholaena dealhata (rarely 

 and locally), PcUaca atropurpurca, Woodsia ohtiisa, and on dry 

 rocky soil Sclaginclla rupestris (rarely). 



THE PRAIRIE REGION 



The prairies lie immediately west of the Missouri river bluffs 

 and in general cover the eastern half of the state, extending farther 

 westward in the southern portion and being much restricted in the 

 northcentral portion. These prairies with their gently undulating 

 surfaces are the western representatives of those characteristic of 

 Iowa and Illinois and are made up of indiscriminately arranged 

 series of low rounded swells or hills interperscd with broad shallow 

 depressions or limited valleys. The soil is of glacial drift which 

 is quite deep in many places and is more or less veneered with 

 loess. Drainage systems are well established and ponds or lakes 

 are uncommon or rare. 



This region is not conducive to fern growth. Where a belt of 

 upland woods occurs Botrychium virginianum and Adiantmn peda- 

 tiim may be found. Onoclea sensibilis and Dryopteris thelypteris 

 occur in wet prairie bottoms. Of the fern allies there are Eqiiisc- 

 tiine arvensc, preferring dry soil, and Equisefum laevigatiim, prefer- 

 ring moist soil. Both species are abundant to common and widely 

 distributed in this region. Equisetitm variegatum is rarely found. 

 In ponds Marsilca vcstita occurs in small numbers or locally abund- 

 ant. Isoetes mclanopoda occurs rarely and locally. 



THE SANDHILL REGION 

 The sandhills lie west of the prairies and cover much of the 

 western half of the state, being confined largely to the central and 

 westcentral portions. The eastern boundary of this region is not 

 well marked, the prairies passing gradually into the sandhills, but in 

 general the boundary line is irregular, receding westward in the 

 river valleys and extending eastward along the watersheds. The 

 greatest eastern extension is in the northcentral portion. The 

 western boundary is quite distinct, although there are outlying sand- 

 hills in the foothill region. The area is about 18,000 square miles, 



