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THE POPULAR SCIENCE MONTHLY 



Fig. 9. A Late Stage in the Reclamation of a Blow-out; the bunch-grasses have 

 now appeared and are creeping up the slope. 



cause of the great exposure to wind and shifting sand. The combined 

 action of a high wind, high soil temperature, excessive evaporation, 

 and an unstable soil in the active blow-out, is a condition that plants 

 can not survive. Sooner or later, however, because the blow-out has 

 reached such a depth that the " sand mill " becomes ineffective and the 

 sliding sand fails to reach the bottom, certain plants appear in the bare 

 sand of the blow-out. From this time the terrible physical conditions 

 begin to wane and the vegetation gradually creeps up from the bottom 

 of the blow-out and slowly becomes the master of the situation. The 

 decadence of the blow-out is traced in the development of the vegetation 

 from these first successful invasions until the* whole crater-like depres- 

 sion is claimed by the bunch-grasses and their common neighbors. 



The first plants to become established in such places are certain 

 grasses commonly called " blow-out grasses." The most important of 

 these is Eedfield's grass (Redfieldia flexuosa) which is almost always 

 the very first pioneer in the reclamation of the blow-out. Redfieldia 

 may be the only plant in such situations for many years. All during 

 this time it is extending its area by undermining and binding the soil 

 with its network of slender rhizomes. From these rhizomes there arise 

 tufts of long, flexuous, narrow leaves gracefully nodding in the gentle 

 breeze or lashing about like so many slender wires in the higher winds. 

 Sometimes in a single windstorm the sand level about these tufts may 



