316 



either the northwest or the southwest winds, either one of which is 

 quite Hkely to be strong. 



In some regions the flora of even quite widely separated blow- 

 outs is remarkably uniform, but this can hardly be said to be true 

 of this region. The blowout is in some measure dependent upon the 

 surrounding associations for most of its species, but there are a few 

 characteristic blowout species which do not occur in associations im- 

 mediately adjoining the blowout; as, for example, green milkweed 

 (Acerates viridifiora lanceolata) , flowering spurge (Buphorbia corol- 

 lata), Cyperus fUicuhnis inacilcntus, Sporobolus cryptandrus, Oeno- 

 thera rhonihipetala, Cyperus schzueinitzii, Corisperniuiii Jiyssopifolium, 

 and horsemint {Monarda punctata) ."ThongXx blowouts occur in sev- 

 eral associations, the association that succeeds the blowout need not 

 be the same as the one in which it started. Blowouts occurring in 

 the Qitercus veliitina association sooner or later give place to Quercus 

 vehiHna, often by passing through a heath stage. Blowouts occur- 

 ring in the heaths may become tenanted by one of several associations : 

 the Qnercus z'clutina, a thicket, the Liatris scariosa, or the L. spicata 

 association. Blowouts in L. scariosa may become occupied by Qner- 

 cus velutina, but more frequently by Liatris spicata ; or, occasionally, 

 by some of the marsh associations, if the blowing should continue 

 during the winter until the bottom of the blowout is below the water- 

 table level. Typical blowouts do not occur in Liatris spicata, but 

 occasionally, where the surface-covering of vegetation has been re- 

 moved by man, blowing ensues. Such blowing does not last long be- 

 cause the sandy bottom is usually damp, and an association such as 

 the Carex oederi pnniila soon obtains dominance and finally reverts to 

 Liatris spicata. Some of these different types of blowouts are shown 

 in Figure 2, Plate LI, Figure 2, Plate LII, and Figure i, Plate LIU. 



Physically a blowout may be divided into four parts. The low 

 central part, or basin, is occupied by the basin association of deep- 

 rooted perennials, such as Acerates viridifiora lanceolata. The wind- 

 ward slope, located on the side from which the sand is being blown, 

 is, with very few exceptions, occupied by the plants of the associa- 

 tion in which the blowout occurs. In the prairie blowouts, the wind- 

 ward slope association is characterized by a species of Panicuni, P. 

 huachucae, a feature which is markedly characteristic of the blowouts 

 at Hanover Station, Jo Daviess County, Illinois (Gleason 1910:79). 

 There, however, a different species, Panicum pseudopnbesccns, is 

 involved. The lee slope, which is directly across from the windward 

 slope, consists of constantly shifting sand, in which the blowsand as- 

 sociation of annuals usually dominates. The lee slope usually ter- 



