NATIVE VEGETATION. 185 



preliensively, that it is entirely inadequate as an explanation of prai- 

 ries in general. 



The Oak group is likewise chiefly confined to the southwestern part 

 of the district. It occupies all classes of topography and all eleva- 

 tions from the lake level to 500 feet above it. It shows a tendency to 

 invade the districts of the heavier forests, along the line of the Kettle 

 Range. This is due to the nature of the soil that accompanies the 

 Range, as will be seen hereafter. 



The Oak and Maple group usually lies contiguous to the last or 

 along the Kettle Range. It was in the latter relationship that its pe- 

 culiarities were first and chiefly noticed. This seems to be due to the 

 fact that the soil is adapted to the Oak group, while the surroundings 

 are favorable to the propagation of the Maple and its associates. A 

 conflict of conditions is the result, in which neither has a decided ad- 

 vantage. 



The Maple group occupies an irregular belt that has a northwest 

 and southeast trend, bordered chiefly by Oaks on the south and Beech 

 and its associates on the north. It is quite distinctly limited in the 

 direction of the Oaks, but much less so toward the Oak and Maple, and 

 the Maple and Beech groups, into which it merges almost impercepti- 

 bly. It reaches from the lake shore to about 500 feet in elevation. 



The Maple and Beech group covers a large surface stretching from 

 the lake shore northwestward, a direction which neither corresponds 

 to geological nor topographical lines, but is none the less instructive 

 on that account. It does, however, correspond very closely with the 

 isothermals for the summer months; l which, with the other elements 

 of the lake influence, as already intimated, are undoubtedly the con- 

 trolling agencies. 



To the north of this the Hardwood and Conifer group extends to Port 

 de Morts, being more extensive than either of the others. The great- 

 est elevation within its area is less than 400 feet above Lake Michigan. 



The Comprehensive group occupies a portion of the crest and west- 

 ern slope of the outcropping rocky ridge of our district. It is limit- 

 ed chiefly to the Green Bay region. It seems to be the result of the 

 conflicting demands of lake and boreal influences, on the one hand, 

 and of soil and warm, dry southwest winds, sweeping up the Green 

 Bay valley, on the other. 



1 See Map of Wisconsin with lines showing the Remarkable Effect of Lake Michigan 

 in Elevating the Temperature for January and Depressing that of July, by I. A. Lap- 

 harn, 1865. Also Transactions Chicago Academy of Sciences, Vol. I, Plate X, 1865. See 

 also, The Isothermal Lines of Wisconsin, by J. G. Knapp, Transactions Wisconsin Hor- 

 ticultural Society, Madison, 1871. 



