145 



and slide slowly down the incline toward the river. Their sides are 

 nearly vertical, and by their detachment the margin of the remaining 

 forest association is left as a prominent vertical wall of coherent sand. 

 The motion of these detached blocks is of course very slow ; but that 

 they are loose is at once demonstrated by stepping on one, which then 

 immediately starts down the slope and in a short time comes to rest on 

 the flat beach at the base of the dune. Their plant population is a 

 relic of the former mesophytic vegetation, and consists largely of 

 perennials with a root system extensive enough to bind the mass to- 

 gether. Some of the commoner species are Lespcdcca capitata, 

 Tradcscantia reflexa, Monarda mollis, Solidago neuioralis. and Ar- 

 temisia caiidata. The more pronounced mesophytes of course disap- 

 pear with the removal of the protecting trees. 



The general trend of vegetation on the river dunes is therefore 

 always toward stabilization, but their permanence is never certain 

 because of the constant changes in the channel of the river. With the 

 destruction of the higher types of vegetation by erosion, the pioneer 

 blowsand association reappears and the successional cycle begins 

 anew. 



The ^ERCiiED Dunes 



In the Hanover area wind-blown sand has collected on top of the 

 high bluffs which border the sand areas, and fomis miniature dunes 

 and blowouts. A number of typical sand plants have colonized upon 

 them, and are usually accompanied by the more resistant species of 

 the uplands or of the rocky hillsides. In the blowouts, which are al- 

 ways small, the vegetation represents the blowsand association and 

 consists of Scutellaria parvula, Linaria canadensis, Monarda punc- 

 tata, Verbena bracteosa, Ambrosia psilostachya, Festitca octoHora, 

 and Hedeonia hispida. On the stabilized dunes there are also Opun- 

 tia Rafinesquii, Artemisia caudata, Amorpha canescens, Lithosper- 

 mum Gmclini, Rhus canadensis, var. illinoensis, Paniciiin pscudopu- 

 bescens, Viola pedata, and Lespedeca capitata. In the sandy soil un- 

 der the oaks are Cacalia atriplici folia, Hypoxis hirsuta, Lithosper- 

 muni Gmclini, Phlox pilosa, Antennaria sp., Anemone patens, var. 

 Wolf gangi ana, Brigeron pidchcllus, Poa pratensis, Coryliis anier- 

 icana, and Jnniperus virginiana. 



Annotated List oe Species 



No attempt was made to secure a complete collection or a com- 

 plete list of the plants living in the sand regions, and the list given 



