NATIVE VEGETATION. 177 



cum stances than natural adaptabilities control the association of these 

 plants, and an effort has been made in the study of the region, to dis- 

 cern these cases and eliminate them from the results, so that the 

 groups which are here given are believed to be natural associations of 

 plants. Their distribution is held to show in what localities condi- 

 tions peculiarly advantageous to them occur, and hence advantageous 

 to those cultivated plants that require similar conditions. 



A. UPLAND VEGETATION. 



(1) Herbaceous. 



CLASS I. Prairie Group. One of the most natural and sharply 

 defined groups is constituted by our prairie vegetation. It differs 

 from all other groups that grow upon the uplands, in being almost 

 exclusively herbaceous, and in the fact that the species composing it, 

 more rarely intermingle with the other groups. It is more distinct 

 from them than they are from each other, and justifies the division 

 of the upland flora into prairie and forest vegetation. Its characteris- 

 tics are too well known to need further definition here. 



(2) Arboreous. 



CLASS II. The Oak Group. This is most nearly related to and 

 most closely associated with the prairie group. The prairies are rarely 

 contiguous to any other form of arboreous vegetation. 



The Burr Oak (Quercus macrooarpa), the White Oak (Quercus alba\ 

 the Red Oak (Quercus rubra\ the Pin Oak (Quercus palustris\ are 

 the most prominent species, and give name to the whole. The Chest- 

 nut Oak (Quercus prinus) is associated with these just north of Janes- 

 ville, but I have observed it at no other point within the state. The 

 common Poplar or Aspen (Populus tremuloides) is the most con- 

 spicuous associate of these oaks, but it is not confined to this associa- 

 tion. The Large-toothed Poplar (Populus grandidentata) is some- 

 times found with this group, but much prefers association with the 

 maples. This and the preceding species are in a sense the comple- 

 ments of each other. Those associations that are avoided by the one 

 are sought by the other, though they not unfrequently mingle. The 

 Populus balsamifera and P. candicans have not been observed min- 

 gling with this group. The Shell-bark Hickory (Carya alba) is an- 

 other prominent member of this cluster. The Pignut Hickory (Carya 

 glabra) is occasionally, but not frequently found in this group. It 

 sustains the same relation to the Shell-bark Hiakory tl at the Great- 

 toothed Poplar does to the Trembling Aspen. The Crab Apple (Py- 

 Wis. SUR. 12 



