CHICAGO AND VICINITT 



37 



are similar over vast areas; the conditions are unique and the flora also. 

 None of our plant societies, not even the lakeward dune slopes, have 

 such a pronounced northern flora as do the peat bogs. No contrast 

 could be more striking than that between the southern vegetation of 



the flood plains and the northern flora of the bogs. 



Fig. IQ shows that a coniferous vegetation, now represented by 



Fig. 20. — Tamarack swamp in an undrained portion of the Calumet flood plain at Miller. 

 Peat bog herbs and shrubs in the foreground. 



but two or three small trees at the centers of the islands, is to follow 

 the Cassandra. Such an advance of conifers on Cassandra is shown in 

 the background at the right. The most typical conifer in such cases 

 is the tamarack [Larix Americana); with this the arbor vitae [Thuya 

 occidentalis) is sometimes found. Larix and Thuya swamps reach but 

 an imperfect development in our region, and little need be said about 

 them. The shade in these forest swamps is so dense that bare patches 

 of soil are often seen. The vegetation consists largely of shade plants, 

 among which may be mentioned Mnium and other similar mosses, 

 Coptis trifolia (Goldthread), Cornus Canadensis, Viola blanda (White 

 violet), and Impatiens. The tamaracks appear to be succeeded by the 

 pines {Pinus Strobus or P. Banksiana), and they in turn by oaks, as 

 the soil becomes drier and better drained, and thus more adapted 



