171 



vegetation which it covers. Small trees are usually killed, but 

 larger ones will withstand burying to a considerable 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, butternut (PL X.), box-elder, 

 and hackberry have also been observed partially buried in the 

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

 has reached such a grove (PI. 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 Solanum nigrum, Euphor- 

 bia heterophylla, Sici/os angulatus, Clematis Simsii,Parthenocissus 

 quinquefolia, Menispermum canadense, Ribes missouriense, Allio- 

 nia nyctaginea, Vitis riparia, Campanula americana, and Urticas- 

 trum divaricatum. The same species occur in the valleys of the 

 Miami loam below. Near the top various photophile forms, 

 such as Cenchrus tribuloides, Monarda punctata, and Asclepias 

 syriaca, appear in great abundance. The three first-mentioned 

 species are evidently pronounced mesophytes, as specimens 

 wilt very rapidly when pulled. Nevertheless, the Solomon is 

 finely pubescent, while the usual mesophytic form in loamy 

 soil is nearly always glabrous. 



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 the sand is removed, 

 when a normal black-soil prairie ensues. 



THE BLACK-JACK ASSOCIATION. 



Throughout the central part of the state the prairie repre- 

 sents the most primitive plant formation. It has been shown 

 that in the sand region, — and the same holds true throughout 



