THE SAND-HILL REGION. 15 



these hasten the depletion of the soil moisture and, if young trees 

 become covered with sand, cause them to be parched to crispness. 



Temperatures are higher at Halsey and Garden City than at Fort 

 Robinson, Nebr., in the heart of the yellow-pine belt of northwestern 

 Nebraska, where precipitation is proportionately less. 



VEGETATION. 



The sand hills of Nebraska and Kansas produce a great variety of 

 grasses, herbs, and shrubs, and a few trees. 



GRASSES. 



The distinctive vegetation of the sand hills, as of most semiarid 

 regions, consists of grasses. The most common and most widely 

 distributed grass is the sand-hill bunch grass (Andropogon scoparius), 

 which indicates a stable soil. The grasses which first come in on 

 loose sand, and which are typical of "blow-outs" and south slopes, 

 are the long-leafed reed grass (Calamovilfa longifolia), which is some- 

 times 4 or 5 feet high, but forms a very light cover, the redfieldia 

 (Redfieldia flexuosa), the eragrostis (Eragrostis tennis), and the 

 prairie muhlenbergia (Muhlenbergia pungens). No less distinct is 

 the switch grass (Panicum virgatum), which forms dense tangles in 

 the rich soil of the dry-bottom situations and is frequently cut for 

 hay. Only in the areas of harder ground, which occur throughout 

 the sand hills, are the grama and buffalo grasses common; these are 

 the most valuable of all the grasses for both summer and winter 

 forage. 



HERBACEOUS PLANTS. 



Some of the most common herbaceous plants are the digitate 

 psoralea (Psoralea digitata) , the prairie thistle (Carduus plattensis) , a 

 broad-leafed cactus (Opuntia polycanfha) , several species of Euphor- 

 bia (spurges, locally called " milkweed"), and the wild sweet pea 

 (Lathyrus ornatus) . Of common weeds the sunflower and the squirrel- 

 tail or tickle grass are the most widely distributed and the most 

 persistent. Russian thistle gains a foothold in the Kansas sand hills 

 wherever sod is broken. 



SHRUBS. 



Of the numerous woody undershrubs the yucca, or soap- weed 

 (Yucca glauca), is probably the most striking plant of the sand-hill 

 region and is least abundant where the soil is the most stable and 

 firm. Other shrubs, most of which are more or less gregarious and 

 form clumps or mats on the ground, are the sand-hill willow (Salix 

 Tiumilis), very common on north slopes and indicative of good mois- 

 ture conditions, 1 the redroot or New Jersey tea (Ceanothus ovatus), 



1 Even the sand-bar and the peach-leafed willows have been found with this smaller species, where the 

 moisture conditions are especially good. 



