2i6 THE POPULAR SCIENCE MONTHLY 



in poorly defined bunches are, however, conspicuous wherever they are 

 found. 



Within the bunch-grass association there are a number of secondary 

 types that are quite well defined. But as one views the vegetation of 

 the Sand Hills in a general way these are lost in the great monotony of 

 the bunch-grass association. However, the vegetation and general life 

 conditions of the uplands, the home of the bunch-grasses, are very notice- 

 ably different from those characters on the river flats or in the wet 

 valleys. The exposure to both the drying and the mechanical effects of 

 the wind is most keenly felt on the uplands, composed of the hill tops 

 and upper slopes. Sometimes the wind sweeps over the crests of the 

 hills with such terrific force that one can not stand in its path and 

 endure the sting of the sand blast. During a bright day with a high 

 temperature and such a wind, life on the hills is well nigh impossible. 

 During the hottest days of summer the surface sand in such situations 

 is frequently heated to a temperature of 140° F. Such conditions with 

 a low water content of the soil and a high saturation deficit are the 

 factors that plants must meet. One can not but admire the vegetation 

 that possesses the power of successfully resisting such a combination of 

 conditions. That Sand Hill vegetation has been very successful in 

 meeting these conditions is fully attested by a glance at the region as 

 we find it to-day and a comparison with the dismal waste of bare sand 

 dunes that once wandered over this same area. 



Aside from the bunch-grasses, the most characteristic plant of the 

 uplands is the dagger weed {Yucca glauca) which often occurs m great 

 abundance on the upper slopes. In certain portions of the region over 

 restricted areas this species really becomes dominant and the bunch- 

 grasses then play only a subordinate part in the floral covering. The 

 dagger weed reaches its best development on the south and west expos- 

 ures, although it is by no means confined to these slopes. The sand is 

 often blown away from the roots for many inches beneath the rosette of 

 bristling leaves, and yet the plant continues to thrive. Frequently it 

 puts out new shoots from the exposed roots and develops new rosettes of 

 leaves beneath the old. 



The so-called " cat steps " formed on steep slopes in the Sand Hills 

 owe their origin to the grazing habits of cattle and very frequently to 

 the presence of dagger weeds. On such slopes the cattle, avoiding the 

 sharp-pointed leaves of the Yucca, follow angling paths which eventually 

 become netted and worn into the sand in such a way as to cover the 

 hillside with a network of trails. Clumps of dagger weed often fill in 

 the more or less diamond shaped meshes of this network. From a dis- 

 tance, such a slope bears a close resemblance to the " cat steps " so com- 

 monly seen on steep slopes in the loess region. The origin is, however, 

 very different. One may find in the Sand Hills a great many stages in 



