Page:Popular Science Monthly Volume 80.djvu/226

222

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 depression 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 Redfield'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