220 CLIMAX FORMATIONS OF NORTH AMERICA. 



east side of a line of prairie sloughs. The prairie, like that of other stations in 

 this part of Illinois, is largely mesophytic; this type is of three appearances: 

 (1) the Andropogon furcaius prairie, (2) the mixed grass prairie, and (3) the 

 Silphium terelnnthinaceum prairie. Mesophytic prairie-grass may be derived 

 either from marsh growths and swamp prairie or fen, small areas of which are 

 still abundant near by, or from xerophytic prairie-grass, represented in the area 

 chiefly by Silphium laciniatum prairie. The markedly xerophytic types of 

 prairie-grass no longer persist in upper Wisconsin glaciation of northeastern 

 lUinois, but are well represented in central and western parts of the State. 

 Sunny forest borders show an outer zone of sunflowers, a shrub zone of dog- 

 wood, occasionally with hazel or aider, and sometimes a low-tree zone, in 

 which plum, thorn-apple, or wild crab may be seen. Shaded borders show less 

 definite and narrower zones, with tall mesophytic herbs, climbers, and usually 

 dogwood." 



The same author (1914* : 377) has made a study of the grassland vegetation 

 along the Front Range about Boulder, Colorado. The associations are 

 grouped into climatic or major, and minor, the latter divided into local or 

 edaphic, and primitive, both developmental in character, and hence to be 

 termed associes or consocies. While the successional relations are not indi- 

 cated, they are readily inferred from the structure and position of the different 

 communities. 



HYDROSERE. 



Gates (1912) has made a graphic summary of his study of the hydrosere 

 about Lake Michigan (see fig. 9, page 221). 



Pool (1914 : 189) summarizes the hydrosere of the sand-hills of Nebraska as 

 follows: 



"The lowland successional series begins with the aquatic pond-weed asso- 

 ciation and follows more or less in correlation with the developing humus 

 complex through the water-lily association to the marsh formation. From 

 this point we have traced the development and structure of the bulrush-reed- 

 grass and smartweed associations with their common variations as they are 

 correlated especially with a decrease in soil-moisture and a receding water- 

 table. As the substratum becomes progressively harder and drier we have 

 witnessed the development of the meadow formation with its rush-sedge wet 

 meadow and other associates, finally leading to the estabUshment of that 

 extensive and valuable tjrpe which I have called the hay meadow association. 

 Rarely is this series interrupted through the operation of the forces that so 

 often affect the regular course of upland successions. The hay meadow 

 appears to mark the culmination of this particular series, yet, whfle the evi- 

 dence is not as complete as it should be, conditions have been observed which 

 indicate that this tj^pe should be regarded as a 'temporary climax.' 



"Certain evidences are prophetic of a still fiuther development from the 

 typical meadow structiu-e to that possessed by one of the prairie-grass associa- 

 tions. Indications of such a possible transition have been observed where 

 the hay meadows and certain prairie associations have become intermingled. 

 Modifications of the hay meadows arising from invasion by Stipa and Agropy- 

 rum have been observed in a nmnber of places. These facts lead to the tenta- 

 tive conclusion that the final vegetative cover of the sand-hills may be com- 

 posed of one or more of the sodr-forming prairie-grass associations and the 

 bunch-grasses will remain as relicts upon the more extremely xerophilous, 

 sandy situations. 



