536 
prairie district. 
Part IV. Chapter 3. 
found on the St. Peter sandstone. 
In Iowa in Winneshiek County‘) the following associations are 
Upon the harder exposed rock surfaces grow the following lichens and mosses: 
Lecanora rubina Vill. 
Physcia caesia Hoffm. 
Parmelia conspersa Ehrh. 
Urceolaria seruposa L. 
Placodium aurantiacum Light. 
Buellia spuria Schaer. 
Bryum intermedium Brid. 
Ceratodon purpureus Brid. 
Dicranellaheteromalla Schimp. 
Upon the upper portion of the ledges in crevices, or on exposed surfaces where a little sandy 
soil had accumulated: 
Cladonia cornucopioides L. 
Cladonia rangiferina L. 
Grimaldia barbifrons Bisch. 
Polytrichum piliferum Schreb. 
Selaginella rupestris L 
Sisyrinchium angustifolium 
Mill. 
Polygala viridescens L. 
(= P. sanguinea L.) 
Linum sulcatum Rid. 
Potentilla tridentata Sol. 
Prunus pumila L. 
Pirus melanocarpa Willd. 
(= Aronia nigra Willd.) 
Scutellaria parvula Michx. 
Where the sandy soil on the rock ledges is greater the following occeur: 
Muhlenbergia glomerata Trin. 
(= M. racemosa Michx.) 
'Aristida basiramea Engelm. 
Bouteloua hirsuta Lag 
Eragrostis Frankii Steud. 
Amelanchier alnifolia Nutt. 
Lespedeza capitata Michx. 
Amorpha canescens Pursh. 
Helianthemum canadense L. 
echea tenuifolia Michx. 
Polygonum camporum Meissn. 
Gnaphalium obtusifolium L. 
= G. polycephalum Michz.) 
Solidago tenuifolia Pursh. 
(= Euthamia caroliniana L.) 
Solidago rigidiuscula T. & G. 
Aster sericeus Vent. 
In the better shaded, or protected. places, the botanist finds Woodsia ilvensis, Rubus Bailey- 
anus (= R. Enslenii), while the sandy talus below the ledges yields Sporobolus brevifolius, Cyp- 
erus filieulmis, Polygonum tenue, P. Douglasii, Solidago nemoralis, Lechea tenuifolia, Helianthemum 
canadense, — deeper soil of the talus and the sandy ledges encourages a tree vegetation: 
Betula papyrifera, Quercus macrocarpa, (). tinctoria, Amelanchier canadensis, A. rotun 
Prunus pennsylvanica, P. virginiana and the usual associated mesophytic herbs. Elsewher 
wetter sandstone grows Marchantia polymorpha, Porella platyphylla, Athyrium filix-foemina, 
Cystopteris bulbifera. 
3. The Grass Formations. 
Grass Formation of High Prairies and Level Sandy Plains. This is empha- 
tically a grass formation and resembles at a distance a typic prairie. It is 
controlled by two grasses which not only furnish the bulk of the vegetation 
and give aspect to the landscape, but sometimes take exclusive possession of 
extensive areas. Siipa comata and Agropyron spicatum (= A. divergens) are 
the ruling grasses usually associated with one or the other predominant. The 
high rolling prairies are controlled by Stipa comata. The level sandy stretches 
where the covering is thin and in patches are dominated by Agropyron 
pseudorepens. | i 
The Stipa formation of high prairies is the chief grass formation of the 
region, where the typic grass forms a sod in which secondary species oCcCUf 
such as Zupinus plattensis, Astragalus mollissimus, A. adsurgens, Oxytr opis 
t) SHIMEK, B.: The Flora of the St. Peter sandstone in Winneshiek County, Iowa. Bulletin 
Laboratories Natural History, State University of Iowa. V. No, 4: 225—220. 
