1912] GLEASON & GATES—RATES OF EVAPORATION 485 
cordiformis. In the typical areas of this association, there are 
neither vines nor shrubs, with the exception of some shrubs remain- 
ing as relics from the prairie, even though the seeds are already 
present in the sand beneath the trees. The presence of Psedera 
quinquefolia and other vines in some places is accordingly considered 
an indication of the approaching succession of the mixed forest 
Fic. 3.—A vests near the station of atmometer no. 8, July 1910; photograph 
by fanaa G. VES 
association. The shrubby growth consists largely of the young 
trees of the dominant species, together with Rhus canadensis, var. 
illinoensis, and Ceanothus americanus, relics from the bunch-grass. 
The herbaceous vegetation but sparsely covers the ground, although 
the number of species represented is usually large. The most com- 
mon and typical are Tradescantia reflexa, Amorpha canescens, 
Euphorbia corollata, Smilacina stellata, Phlox bifida, Verbascum 
Thapsus, Monarda fistulosa, Lithospermum Gmelini, Aster azureus, 
Rudbeckia hirta, Lespedeza capitata, Pentstemon hirsutus, Asclepias 
tuberosa, Tephrosia virginiana, and Rosa humilis. The soil is sand 
