103 



is not homogeneous from this point of view ; it is a mosaic composed 

 of a number of minor social communities. Each of these smaller units, 

 however, is fairly homogeneous throughout. 



Our present knowledge of these minor associations is imperfect, 

 and for this reason they are arranged in an order approximating that 

 which we might reasonably expect to be produced if the initial stage 

 were made to begin with a poorly or imperfectly drained area and to 

 advance progressively with corresponding vegetational changes, toward 

 a more perfect condition of drainage. Upon the prairie a perfect series 

 would include every stage from lakes, ponds, and swamps to well- 

 drained dry prairie. But cultivation and drainage have obliterated so 

 much, that now only very imperfect remnants exist in the vicinity of 

 Charleston. Although the sequence followed therefore does not in- 

 clude all stages of the process it is approximately genetic. 



There are three essential features in every animal association, or 

 community; certain physical conditions; certain kinds of vegetation, 

 which also modify the physical conditions; and representative kinds of 

 animals. Occasionally an effort is made to divorce these, to separate 

 organisms from their normal habitat, but such an effort is deceptive, 

 for no organism can live for any considerable period without a normal 

 environment. 



I have not attempted to treat these associations with equal fullness. 

 In the sections devoted to the description of the stations it was possi- 

 ble in some cases, on account of the uniform character of a station, to 

 describe the animal association rather fully. In such instances the 

 detailed account is not repeated. In other cases I have elaborated the 

 community relations more fully here than elsewhere. The descriptions 

 of the stations and the associations, and the annotated lists, are in- 

 tended to be mutually supplementary. 



II. The Prairie Associations 



I. Szvainp Prairie Association 



The swamp prairie community lives in a habitat characterized by 

 shallow water, which stands approximately throughout the growing 

 season of the vegetation. The soil is black, and rich in vegetable de- 

 bris. The characteristic plants are bulrush (Scirpus), flags (Iris), 

 swamp milkweed (Asclepias incarnata), beggar-ticks (Bid ens), and 

 young growths both of willow (Salix) and cottonwood (Popnliis del- 

 toides). The abundant growth of vegetation and the wet soil are con- 

 ditions favorable for the production and accumulation of organic de- 

 bris, which tends to fill the depressions and to supplement the inwash 



