297 



consocies. Some of these have been described for southeastern South 

 Dakota by Harvey (1908) and for the Illinois sand areas by Gleason 

 (1910). Of these consocies only one appears as a definite part of the 

 region in this area. That is the Andropogon scopariiis consocies, 

 which has been described as a pioneer of prairie vegetation by Han^ey 

 (1908:287). There are, however, clear indications that other con- 

 socies have been represented which are now succeeded by forest as- 

 sociations. Some of the bunch-grasses, which were once dominant 

 species, are now relics, living as secondary species in the Qucrcus 

 velutina woods. 



The association itself is open, since but 25 to 40 per cent, of the 

 area is vegetated. Approximately 90 per cent, of the vegetated area 

 is occupied by the dominant species, Andropogon scoparius. The sec- 

 ondary species may be more numerous, but they are interstitials that 

 occupy very little surface. Figure 2, Plate L, shows the general ap- 

 pearance of the association throughout the year, and exhibits the 

 manner of growth of the dominant species. 



Andropogon scoparius- — As shown in Figure 2, Plate L, this grass 

 is a typical bunch-grass. The dead leaves remain over winter and until 

 the new leaves grow. They do not seem to be capable of retaining blow- 

 ing sand, and so this grass is not a dune-former. It can fix dunes, 

 however, but not until the dune has been built up by some regular 

 dune-former. The plant spreads radially, but very slowly as it has 

 no runners. The spreading continues until the diameter of the stool, 

 or bunch, is from 3.0 to 3.5 decimeters. It does not often grow larger 

 than this. Occasionally bunches are to be found in which the cen- 

 tral part is dead, the circle of stems around it forming a small fairy 

 ring. Other plants become established in the center, and tend to lead 

 to the gradual replacement of the bunch-grass. Arabis lyrafa and 

 shrubby cinquefoil (Potenfilla fnificosa), an invader, are most fre- 

 quent in this role. Others that have been found so situated are 

 Arenaria stricta, Oenothera rhonibipetala, blue-eyed grass (Sisyrin- 

 chiuni sp. ?),and Artemisia caudata. In this area the bunches them- 

 selves are always separated, usually by about eight to nine decimeters 

 The more pebbly the area, the greater the tendency for the bunches to 

 be nearer together, but seldom closer than five decimeters. The bunches 

 which are invading the Artemisia-Panicnni are developed just as well 

 as those in the bunch-grass itself. 



The area between the bunches is occupied by interstitials, which, 

 how^ever, are not sufficiently abundant to prevent the sand from giv- 

 ing the general color-tone. In point of numbers rock cress (Arabis 

 lyrata) is most abundant. When it is well in bloom, in May, the 



