vegetation whicli it covers. Smail trees are usually killed, hut 

 larger ones will withstand hni-ying to a considei-able depth. 

 Frequently the only sign indicating the former position of a 

 blowout is a Cottonwood tree (PI. IX.) buried to its lower 

 limbs, but still alive. Walnut, liutternut (PI. X.). box-elder, 

 and hackberry have also been ol)served partially luiried in the 

 same manner. The vegetation of the front of a dune which 

 has reached such a grove (PL XX., Fig. 2) is quite different 

 from that of a dune advancing in the open. The sand, shaded 

 and protected from evaporation, is much moister in the upper 

 layers, and the face of the dune is at a steeper slope. The her- 

 baceous vegetation is sparse, probably because of the weak 

 light, since in the sunnier spots the individual plants are more 

 numerous. The principal species are Sulinnini niijniiu. Kifjilinr- 

 lini hctcriiiilnilld . Siciftis (ni<iiil<ifits, Clcnintis Sni/si / .1 '(irf//ri/i:'''ssiis 

 (iHi iKiKcfnl III . Mni isjii rill II III rii iiiiilviisf. Itiliix in issail ririisr. Allio- 

 iiiii II i/cfiii/i iini, I if IS npii rill , Cii III jKi iiiilii iniimniii'i. iU\(\ I rficus- 

 fniiii iliniriciitiiiii. The same species occur in the valleys of the 

 Miami loam lielow. Near the top various photophile forms, 

 such as ( 'ry/rA/v/,v frilniliiiilrs. Miiiiiinlii jiinirtnfii. and Asrlrpms 

 si/i-iiiiui. appear in great abundance. The three first-mentioned 

 species are evidently prononnced mesophytes, as specimens 

 wilt very rapidly when i)ulled. Nevertheless, the Sohimiiii is 

 finely juibescent. while the usual mesophytic form in loamy 

 soil is nearly always glaln'ous. 



To summarize the preceding statements concerning the 

 development of plant associations from the bunch-grass, the 

 action of the wind may lead to the development of the blow- 

 sand and the blowout associations, but either of them may 

 normally revert to the bunch-grass association unless the blow- 

 out excavation has continued until most of tiie sand is removed, 

 when a normal black-soil pi'airie ensues. 



THE BL.\CK-.J.A.CK .ASSOCIATION. 



Throughout the central part of the state tlu' i>rairie repre- 

 sents the most primitive plant formation. It has been shown 

 that in the sand region.^and the same holds true throughout 



