30 IOWA ACADEMY OF SCIENCES. 



itat, and that while their seed may be scattered broadcast, only 

 that will grow and blossom and bring forth fruit which falls 

 within those conditions which render its existence possible. 

 It is not probable that widely, separated regions owe the simi- 

 larity of their floras wholly to the accidental dropping of a 

 few seeds. The floras of the Sioux Quartzite and of a portion 

 of Muscatine county are in many respects similar, and quite 

 unlike the intervening flora, yet it is not improbable that the 

 broad area lying between them was once covered by their own 

 kind. 



Where distinct floras, requiring conditions for the best 

 development, are brought as close together as is the case in the 

 region under consideration, it is evident that with any con- 

 siderable change in amount of rainfall one of the floras would 

 suffer. With a comparative abundance of rains the alluvial 

 and aquatic floras would have the advantage and would crowd 

 upon their drouth-loving neighbors; while with a scarcity of 

 rain these conditions would be reversed. A number of very 

 wet or very dry consecutive seasons might therefore materially 

 change the character of the flora of such a region. If, how- 

 ever, a general average was preserved, the dry soil and rock 

 species would be at a disadvantage in the end, for they would 

 gradually prepare a soil for their greedier neighbors who 

 would slowly creep out upon their territory and finally take 

 complete possession of it. 



The study of such regions as that which includes the Sioux 

 Quartzite exposures in Iowa, if conducted systematically and 

 for a long period, ought certainly to throw light on the ques- 

 tion of the succession of floras in the northwest. 



TABLE I. 



Species from the alluvial and richer soil 

 The species marked * were collected only at the first or eastern exposure. 

 With two exceptions they are herbs, which do not appear in the list of the 

 preceding year, having- probably disappeared by the month of August. 



* Allium canadense Kalm. Parietaria pennsylvanica Muhl. 



*Amorpha fruticosa L. Phlox pilosa L. 



Ampelopsis qy/iriquefoHa Mx. Prunus virginiana L. 



*" Anemone pennsylvanica L. Ranunculus abortivus L. 



Anemone virginiana L Rhus glabra L. 



AquHeaia canadensis L. Rhus toxicodendron L. 



Celastms scandens L. Ribes floridum L'Her. 



Ci II is orcidi at <t lis L. Ribes gracile Mx. 



■ KHisin ni/ctelea L. 1 tubus strigosus Mx. 



