iq2o] TAYLOR—SUCCESSION OF MOSSES 453 



shore line, thus cutting off portions of the lake, which then became 

 lagoons. At one time these ponds drained either into the Calumet 

 River or directly into Lake Michigan. Much of this drainage has 

 been cut off by railroad embankments built across the ridges and 

 lagoons, so that these depressions now exhibit a characteristic pond 

 flora. Some of the ponds have reached the shrub or swamp-forest 

 stage; others are dominated by an almost pure stand of cat-tails 

 or bulrushes; still others, ecologically younger, have a consider- 

 able area of open water. The ridges in most cases are covered 

 with oak forests. 



In addition to the lagoons, hydrophytic habitats are to be 

 found in various swamps and bogs which lie within the Chicago 

 region, all of which offer excellent conditions for bryophytic 

 development. These may be divided into two main types, those 

 which have developed from deep kettle lakes and those which have 

 been formed from shallow lakes or ponds. The former type is 

 illustrated by the bogs at Mineral Springs and Hillside, Indiana; 

 while the latter is represented by the swamp forests at Thornton, 

 Illinois, and Furnessville and Wilhelm, Indiana. The Mineral 

 Springs bog has been developed by marginal encroachment of 

 vegetation on the bottom and by formation of a surface mat in 

 which Decodon verticillatus has played an important part. The 

 progression has passed beyond the open water of floating vegeta- 

 tion stage, and even the early stages of mat formation seem to be 

 somewhat telescoped ; but here and there are small areas in which 

 either the cat-tails, the bulrushes, or the sedges are dominant. 

 This fen association merges into the shrub stage in which Rhus 

 vernix, Cephalanthus occidentalism and Alnus incana are most 

 abundant. Beyond the shrub association is the tree area with 

 Larix laricina, where in places the quaking condition is still quite 

 evident. In the drier portions of the forest Betula lutea, a tree 

 rare in the vicinity of Chicago, makes its appearance. The Hill- 

 side bog seems to have had the shrub stage, which here comes in 

 on a dense growth of Sphagnum, continued until the substratum is 

 comparatively dry, the forest stages having been subjected to a 

 much greater retardation than is the case at Mineral Springs. 

 The other swamps mentioned have been produced by marginal 



