SOME SOURCES OF OUR FAUNA AND FLORA 295 



Whence then came the plant and animal immigrants that 

 replenished our barren region? Briefly stated, the facts are 

 these. Certain elements of our present fauna and flora are 

 relics of the tundras and the coniferous forests. In addition, the 

 sterile land uncovered by the retreating glacier was gradually 

 repopulated by immigrants from at least three centers, one an 

 arid region in the southwest with whose fauna and flora ours has 

 many affinities. A second center was in the southeast; from it, 

 for example, have come most of our deciduous forest trees and our 

 river clams. ' The third region from which ours has received con- 

 tributions is the Atlantic Coast plain. Many animals and plants 

 of the shores of the Great Lakes are identical with those of the 

 eastern seacoast. And finally there is a very perplexing factor in 

 that the only close relatives of certain of our plants and animals to 

 be found anywhere in the world are along the eastern coast of Asia. 



There are no remnants of the tundra formation in the immedi- 

 ate vicinity of Chicago, for such exist in eastern North America 

 only in isolated patches on the mountain tops. Such are found 

 in the Great Lakes region on the high hills of northern Wisconsin 

 and Michigan. As examples of such forms may be mentioned 

 the dwarf grass, Agropyron biflorum, the herbaceous willow, Salix 

 herbacea, a very low form with an underground stem that lies in 

 the wet mosses, Rhododendron lapponicum, Arctostaphylos alpina, 

 some dwarf blueberries, Vaccinum oliginosum and V. caespitosum, 

 mosses and lichens such as the Cladonia rangiferina. 



There are, in the pine association of the Dunes, as already 

 noted, extensive areas with a distinct boreal character. Here 

 flourish Pinus strobus, P. Banksiana, together with the arbor 

 vita, low and spreading junipers, such boreal shrubs as prince's 

 pine, shinleaf, arbutus, northern herbs like star flower, false 

 lily-of-the-valley, etc. There are scattered remnants of this 

 coniferous society on rocky hills elsewhere, particularly on their 

 dry crests and cold northern slopes. Associated at times with 

 these p'ants in the Dunes, but elsewhere in our region quite 

 isolated, is another subarctic formation, the sphagnum- tamarack 



