228 NATURAL HISTORY BULLETIN. 



Festuca octoflora Walt.. Polygonum douglasii Greene 



Sporoboliis brevifolius (Nutt. ) Nash. Polygonum tenue Ms. 



Cvpe r its filiculmis Vahl. Solidago nemoralis Ait. 



and stunted forms of Helianthemum eanadensc (L) Mx. and Lechea 



tenuifolia Mx. 



Also the following introduced weeds: 



Chcctoehloa glauca (L. ) Scrib. Rumex acetosclla L. 



Synthcrisma liucarisilLroc'k. )Nash. Lepidium virginicum L. 



Syntherisma sanguinale (L. ) Dulac. Oxalis stricta L. 



Poa pratensis L. Nepeta cataria L. 



Polygonum aviculare L. Ambrosia artemisicefolia L. 



Polygonum convolvulus L. Leptilon eanadensc (L. ) Britt. 

 Polygonum pennsylvanieum L. 



Both the talus and the sandy soil on the ledges gradually 

 shade off into deeper and better soil, and trees and shrubs, 

 such as Betula papyrifera Marsh., Quercus macrocarpa Mx., 

 Quercus velutina Lam., AmclancJiicr canadensis (L.) Medic., 

 Amelanchier rotundifolia (Mx.) Roem., Pninus pennsylvanica 

 L., Primus virginiana L-, etc., and their accompanying meso- 

 phytic herbs, were found, but it is scarcely proper to refer 

 these to the flora of the St. Peter sandstone. 



In the same doubtful category should be placed Marchantia 

 polymorplia L,., Porella platyphylla Lindb., Athyrium filix- 

 foemina (L.) Roth, and Cystopteris bulbifera (L.) Bernh , 

 which were found upon moist rocks in sheltered places. 



It will be noticed that with these exceptions the flora of 

 the St. Peter sandstone is almost wholly xerophytic. More 

 permanent terrestrial xerophytic areas in Iowa are practically 

 limited to the following: 



Unsheltered rock exposures of comparatively limited extent. 



Higher sands not subject to frequent overflows, including 

 secondary sandy terraces and sand-dunes. 



Dry ridges in wooded areas, usually rocky or gravelly, 

 sometimes loess-covered. 



Dry prairies. 



Ordinary sand bars may also be included, but the fact that 

 they are subject to frequent overflows renders the conditions 

 which exist on them somewhat mixed, and subject to rapid 

 change. 



