80 



wind action, it does not occupy lar^e continuous stretches, but occurs 

 in isolated tracts of g-enerally small size (PI. Ill, Fig. 2). It also 

 shows a veiy definite space relation to the bunch-g'rass association and 

 to the blo^^■out associations. The former is normally found at the west 

 and northwest, and the latter are at the east and southeast of the Pan- 

 icnin pseiidopubescens association. This is caused by the prevailingdy 

 west and northwest winter winds, together with the successional re- 

 lations of the associations. 



The circular depressed bunches of the dominant species have al- 

 ready been described under the bunch-g"rass association. They may 

 grow in almost pure association, as far as other bunch-forming 

 grasses are concerned, or may be somewhat mixed with other species. 

 The additional species, however, are never sufficiently abundant to 

 give the general tone to the association, thereby assuming dominant 

 rank. The bunches are separate or confluent in small irregular 

 patches. The inten^ening areas of bare sand may be two or three 

 feet (6-10 dm.) across, and are invariably conspicuously depressed 

 between the bunches. The elevated position of the bunches gives them 

 an appearance of prominence and individuality not found in the 

 bunch-g'rass association. Two other bunch-formers, Carex iinibeUata 

 and Panicnui pcrlonguin, appear quite frecjuently. The former pro- 

 duces very dense, flat, circular bunches 1-1.5 feet (3-5 dm.) wide, 

 with narrow, stiff, short, closely aggregated leaves. The bunches are 

 conspicuously elevated, sometimes six inches (1.5 dm.), and the larger 

 ones are invariably dead in the center, thus producing a growth-ring. 

 The outer edge of living plants stands at a conspicuous angle, and 

 the dead center is a few inches above the general level of the sand. 

 The regular hemispherical bunches of Panicnui pcrlonguin have al- 

 ready been described. In this association they gTow somewhat more 

 depressed, approaching in structure those of Panicum pseudopuhcscens. 

 Carer uuihcUafa scarcely occurs beyond this association, while Pani- 

 cuni pcrlonguin is found in the bunch-grass as well. The amount 

 of ground space occupied by these three plants probably never ex- 

 ceeds /=^ per cent., and may be less than 50 per cent. 



Se\'eral other species of bunch-g'rasses which occur scattered at 

 wide intervals must be regarded as relics of a former bunch-grass 

 association. They vary in species from station to station, and in 

 number of individuals inversely with the age of the association. 

 They are never abundant, but are frequently veiy conspicuous be- 

 cause of their larger size or erect liabit of growth. The species of 

 this character are as follows : 



