246 MINNESOTA BOTANICAL STUDIES 



which are normally distributed in the form of a close network with 

 many fine rootlets spreading throughout the meshes, there arise 

 few-leaved tufts of long, narrow, flexuous leaves. This species can 

 endure longer periods of severe wind-whipping than any other simi- 

 lar plant of the region. The rhizome method of propagation and 

 the ability to recover after being buried or uprooted are noteworthy 

 characteristics possessed by the common blow-out pioneers. Espe- 

 cially are these phenomena characteristic of, and most highly devel- 

 oped in, RedHeldia Hexuosa, Psoralea lanceolata, Muhlenhergia pun- 

 gens, and Calanwvilfa longifolia. 



The time required for the complete fixation of the sandy soil of 

 a blow-out through the agency of invading plants has never been 

 determined. Studies have been begun which should in the course of 

 years throw some light upon this question. Permanent quadrats 

 have been established within certain blow-outs and careful complete 

 lists of species and individual plants have been made for the same 

 three large, comparatively young blow-outs in the hope that some 

 data may be collected bearing upon the time that elapses between 

 the first successful establishment of vegetation within a blow-out 

 and the final (or semifinal) occupation of the same areas by the 

 bunch-grass association. 



As the tufts or erect offshoots of the pioneer species increase in 

 number with the spreading of the hypogean stems, the soil becomes 

 much more stable and conditions gradually arise that make it pos- 

 sible for the incoming and establishment of certain principal and 

 secondary species although the plant cover may still be very sparse. 

 These later arrivals are not numerous but are fairly constant. 

 Eragrostis trichodes, Eriocoma cuspidata, Pentstemon haydeni, and 

 Polanisia trachysperma are the more common and typical species 

 that become a part of the blow-out association at about this time. 

 The latter species with Crista tella jamesii are regular pioneers in 

 sand-draws as will be noted again in the following pages. In addi- 

 tion to these plants, which with the dominant species may be 

 regarded as the most characteristic and frequent members of the 

 blow-out association, there are numbers of the regular members of 

 the bunch-grass association that come into the blow-out. The com- 

 ing of these species usually indicates a considerable degree of stabil- 

 ity already attained within the blow-out and is prophetic of the 

 ultimate establishment of the bunch-grass association in the regular 

 normal progress of succession. The more common and abundant 



