1910] Bruncken, Studies in Plant Distribution. 155 



impossible to distinguish various sub-associations, as has been done 

 for the inland forests. 7 To them is added a number of species not 

 found elsewhere near Milwaukee, or only in a strip along the 

 shore, scarcely more than a mile wide. These are Pinus strobus, 

 Thuya occidentalis, Tuniperus nana, Juniperus virginiana, Populus 

 balsamifera, Betula alba.* They are all frequent farther North. 

 Larix Americana, which is elsewhere found growing in swamps, 

 is growing here on the steep banks. Accompanying these trees are 

 various dwarf shrubs and herbs, also found commonly farther 

 north and in association with white pine and paper birch, but not 

 found elsewhere near Milwaukee ; or, if at all, only in the "boreal 

 islands" of the tamarack swamps. Such are: Shepherdia cana- 

 densis, Pedicularis canadensis, Ptelea trifoliata, Pyrola rotundi- 

 folia, Habcnaria hyperborea, Castillcia coccinca, Lilinni Philadel- 

 phia! in and Parnassia caroliniana. 



It is not. apparently, the undoubted xerophily of the trees and 

 some of the herbs and dwarf shrubs just mentioned, that makes 

 them occur in this area. The pine, arbor vitae, juniper, tama- 

 rack and balsam poplar are all of prevailing northern range. All 

 of them, to be sure, are found farther south than Milwaukee, but 

 probably in all the more southern stations, some similar local 

 conditions will be discovered if the examination is thorough 

 enough. In other words, like the tamarack and Bricacece bogs 

 elsewhere, the Lake Shore is a boreal island. 



Nor do these northern species seem to be unable to hold their 

 own in the competition with the mesophytic species prevailing in- 

 land, and which also form the greater part of the inhabitants of 

 the shore area. Reproduction of the pine, arbor vitae, juniper and 

 birch is good in all places where they have to contend with no 

 adverse circumstances except -mesophytic competition. In fact, 

 at present nearly all these trees are young, old specimens having 

 been removed by human hands. Yet there is some evidence left, 

 that within recent years they attained considerable age and dimen- 

 sions. 



There is a paper birch stump near Whitefish Bay, 26 inches in 

 diameter two feet from the ground. Tamaracks were measured 



7) See former bulletins of Wis. Nat. Hist. Society, New Series. 



8) The only wild specimens of paper birch I know of away from the 

 Lake Shore are a few small trees on the rocky bluff in the Soldiers' Home 

 Grounds. There are a few young balsam poplars at the mouth of Honey 

 Creek, in Wauwatosa. 



