372 IOWA ACADEMY OF SCIENCE Vol. XXV, 1918 



Societies : 



( 1 ) Spring aspect : 



Viola pedata, Pediculoris canadensis, Phlox pilosa, Bap- 

 tisia bracteata, Sisyrinchium angustifolium. 



(2) Summer aspect: 



Brauneria purpurea, Lilium philadelpjiicum, Amorpha 

 canescens, Heuchera Americana, Psoralen argophylla, Eryn- 

 giuni yuocaefolium, Desmodinni illinoense, Lespedeza ca-pr- 

 tata, Lespedeza leptostachya. 



(3) Fall aspect: 



Aster multiflorus, Llatris pycnostachya, Liairis squarrosa, 

 Gentiana puherula. Aster azure us, Aster sericeus. 



Fig. 146. — Anemone patens Hill. West end of Alluvial Basin to the right. 



The amount of rainfall and seasonal low or high temperature 

 retards or hastens the time of appearance as well as affects the 

 abundance and stature of most of these species. Lilium philadel- 

 pliicum (consoc. II) shows marked reaction to seasonal condi- 

 tions. 



Variation in soil within small areas causes alteration in conso- 

 cies, eliminating .certain members ; for example, the gravelly top 

 of the Anemone patens hill, and tlie two lobes of the Heuchera 

 hill have similar consocies. On the crest of Heuchera hill is a 

 sma.ll knoll, more gravelly and drier than the ininiediately sur- 

 rounding region. Here the si)ecies are sparsely arranged and 

 some are eliminated, Bouteloua liirsuta and Oenothera serrulata 

 being the principal survivors of tins condition. The northeast 

 crests of these hills ai-e i)i'a('ti(':illy identical in physical struc- 



