290 



em border of the bunch-grass prairie, to be described later. One 

 of these dunes was occupied by the following species : cottonwood 

 (Popidus deltoides) (2 meters in hight), Salix glaucophylla, Salix 

 syrticola ( a relic), Calamovilfa longifolia, and Potentilla fruticosa. 

 The other example had the following plants : Sali.v syrticola, lunciis 

 balticiis lit f oralis, Ely inns canadensis, Salix longifolia, Populus del- 

 toides, and Poteniilla anscrina. 



Once in a while a well developed Salix glaucophylla or Salix long- 

 ifolia will form miniature dunes. The branches bend down to the 

 ground, and beneath their shelter sand and debris gradually accumu- 

 late. In the debris are seeds of various plants, notably the winged 

 ones of species of Popidus and Salix. In rifts where sufficient light 

 may be had, a number of plants which could not obtain a foothold on 

 the open sand may get a start. The following species w^ere observed : 

 strawberry (Fragaria virginiana), rock cress (Arabis lyrata), flea- 

 bane (Brigeron philadelphicus), silverweed {Potentilla anserina). 

 Panicum virgatmn, Artemisia caudata, Zizia aurea, touch-me-not 

 {Impatiens bidora), dandelion {Taraxacum erythrospermum), and 

 sweet clover {Melilotus alba). Seedling Popidus deltoides w'ere also 

 present, which indicates that a Populus-Salix dune is being formed. 

 Popidus deltoides itself when growing on sand in this region does not 

 form dunes. Species of Salix, which afford a ground protection to 

 retain sand, at the same time serve to catch Populus seeds. Normally 

 a thicket should be formed, but as yet the ground is too poor in food 

 materials to support the mesophytic species of the thicket association. 



THE SALIX GL.A.UCOPHYLLA DUNE ASSOCIATION 



A few dunes formed entirely by this plant were observed near 

 Kenosha, one of which is shown in Figure 2, Plate XLIX. The 

 dunes are low and elliptical in shape, while the major axis, which 

 runs north-northwest, is about twice as long as the minor axis. 



THE PANICUM VIRGATUM DUNE ASSOCIATION 



During the growing season a small dune may be built up around 

 a tuft of Panicum virgatum, but such dunes are temporary, as they 

 do not w'ithstand the winter. As a rule these dunes have no other 

 species than the Panicum upon them, but occasionally Arabis lyrata, 

 Salix syrticola, Poa compressa and Poa pratensis occur around the 

 edges of the tuft of Panicum. 



