THE NEBKASKA SAND HILLS. 285 



melanocarpa), several acres in extent are common in such places. Green 

 ash (Fraxinus lanceolata), Cottonwood (Populus sargentii) and willow 

 (Salix nigra, S. longifolia) also thrive on this soil. In the plum thickets 

 near the river the vegetation often becomes so dense that it is almost 

 impossible to penetrate to the river's edge. The soil in these places is 

 very rich and moist, so that many species of the shade plants of moist 

 rich woodlands find in such thickets very favorable conditions. On the 

 open areas of the river flats buffalo grass and grama grass constitute 

 the best forage known in the Sand Hills. These low, sod-forming grasses 

 are especially valuable as winter forage. 



Wet valleys are very common in the northern portion of the Sand 

 Hill region, where the valleys are usually broad and long. The water 

 table is near the surface in these valleys, so that the soil in many places 

 is very wet and swampy. There are in this portion of the hills many 

 gradations from the moderately dry hay valley through wet meadow val- 

 leys to valleys with large ponds or lakes. Hundreds of lakes occur in 

 such situations throughout the northern half of the Sand Hill region. 

 There have been two general kinds of wet meadows distinguished. The 

 rush-meadow type is characterized by the presence of a number- of rushes 

 (Juncus tenuis and J. nodosus), and bulrush (Scirpus atrovirens and S. 

 americanus). With these occur a few moisture-loving grasses, such as 

 lowland rattlesnake grass (Panicularia nervata) and whorl grass (Cata- 

 brosa aquatica). In the wet valleys along the Loup River and in Cherry 

 County and in wet places on the river flats a second type of wet meadow 

 is seen in the fern meadow. Shield fern (Dryopteris thelypteris) and the 

 sensitive fern (Onpclea sensibilis) often occur in great quantities in such 

 places with a mixture of willow herb (Epilobium lineare), St. John's v/ort 

 (Hypericum virginicum), goose grass (Galium trifidum) and marsh bell- 

 flower (Campanula aparinoides). Frequently the ferns are so dense as 

 to cause considerable difficulty in walking through this type of wet 

 meadow. 



There are two kinds of lakes in the Sand Hills, depending upon the 

 amount of dissolved substances in the water, alkali lakes and fresh water 

 lakes. It has been found that the alkalinity of the lakes varies between 

 rather great extremes, even the freshest of the fresh-water lakes being 

 somewhat saline. Whatever may be the cause of this gradient in alka- 

 linity, it is an obvious fact that the degree of alkalinity exerts an influ- 

 ence upon the vegetation. In many of the more strongly saline waters 

 scarcely any vegetation appears, although the beach may be well clothed 

 with rushes, sedges and salt-grasses. Frequently even the beach, many 

 feet back from the water's edge, is so thoroughly impregnated with salts 

 that they crystallize over the surface. This results in an absolutely bar- 

 ren zone. Back of that portion of the beach washed by the waves the 

 salt-enduring plants develop very copiously. The salt-grass (Distichlis 

 spicata) is often controlling in such places where the low plants develop 

 a very close tenacious sod. Beyond the belt of salt-grasses the 

 taller stems of other grasses, sedges and rushes make up another dis- 



