FLORISTIC FEATURES OF A PRAIRIE PROVINCE 387 



Cutting does not change the constituent character of the high- 

 land plants. 



Pasturage introduces ruderal plants but most of these do not 

 affect the associations which approaich hydrophytic ar xerophy- 

 tic- conditions. 



Most ruderal plants flourish in mesophytic conditions so that 

 hydrophytic or xerophytic prairie types seem to have fewer coan- 

 petitors than mesophytes. 



Fig. 161. — Zone of wood bordering Squaw creek. Populus deltoides ami 

 Salix along the edge. Crataegus mollis and Pyrus iowensis advancing 

 toward tlie prairie. 



SUMMARY. 



Geology. This area is underlain by rock of the Carboniferous 

 system and Paleozoic group. The present drift deposit of this 

 area is the Wisconsin of the Pleistocene system and Cenozoic 

 group. 



TopograpJuy. The territory observed consists of: (1) Allu- 

 vial basin probably the pre- Wisconsin bed of Skunk river which 

 may have drained a region now occupied by the head waters of 

 Des Moines river; (2) Morainal deposits between the arm of 

 Skunk river and the bend in Squaw creek near Ames. 



Edaphic features. The soil types involved are alluvial, sand, 

 sandy loam, loam, gravelly loam and clay loam. 



(a) Water Content. It is shown by the graphic data that (1) 

 the lowlands contains a materially higher percentage of water 

 than the uplands. (2) There is greater divergence in the per- 

 centage contained by the upland surface, subsurface and subsoil 

 than in these corresponding zones of the lowland. (3) The water 

 table of the lowland is quite constant, showing a gradual dip in 

 the autumn. (4) The subsoil cun-e of the upland is variable, 



