THE FLORA OF THE ST. PETER SANDSTONE. 2 29 



In its ecological characters the St. Peter sandstone com- 

 bines more or less the qualities of all these areas. Its more 

 indurated ledges furnish the exposed rock; its talus supplies 

 all the conditions of the sand-area, and the gradually in- 

 creasing sandy soil which extends back from the tops of 

 the ledges, is equivalent in character to the dry ridge 

 and prairie. Consequently we find a blending of the floras 

 of these several areas. The lichens, bryophytes and pterid- 

 ophytes point to a relationship with the flora of the Sioux 

 Ouartzite in the extreme northwestern part of the state; such 

 forms as Linum sulcatum, Scutellaria parvula, Helianthemum 

 canadense, LccJiea tenuifola, Aster scriccus, Sisyrinchium 

 augustifolium, Polygala viridesceus, etc., recall the dry, often 

 sandy-ridge flora; the grasses, sedges, Polygonums, etc., sug- 

 gest the flord of the higher sand-bars and dunes of Muscatine 

 county; while Lespedeza capitata, AmorpJia cancscens, Solidago 

 rigidiuscula, etc., connect this flora with that of the dry 

 prairies, which blend westward with the almost desert-like 

 loess and drift ridges of the western part of the state. 



By no means the least interesting part of the flora is that 

 which has been comparatively recently introduced. At least 

 thirteen species of common weeds have demonstrated their 

 great adaptability to evironment by flourishing, — if that 

 term is permissible under the circumstances, — upon the sandy 

 talus of the areas under discussion. They are much reduced 

 in size, but flower and fruit freely. These sandy areas are 

 unlike ordinary sand-bars, because the}- are not subject to 

 overflow, nor are they like the sand-dunes, on which the con- 

 stantly shifting sands make the existence of many plants 

 impossible. These sands are more permanent, and will remain 

 in their present condition for a long time, since there is a 

 constant gradual addition of sand from the ledges above. The 

 interesting question arises, — will these more permanent con- 

 ditions finally give rise to distinct races, or forms, or varieties, 

 of the plants which have been introduced either from other 

 native floras, or as weeds ? 



