482 BOTANICAL GAZETTE [juxe 



the pannes, and the vegetation varies from the submerged species 

 in deep water to the forests on the drier ridges. Floating in the 

 deeper lagoons and sometimes emerging in the more shallow ones 

 is a large quantity of Drepanocladus fluitans, D. aduncus, and 

 Campylium chrysophyllum, and perhaps other closely related 

 species. Around the margin of many lagoons are C. stellatum, 

 already mentioned for the pine pannes at Miller, and Bryum 

 ventricosum, which has also been found at Long Lake and Pine 

 in much the same situations. In the larger lagoons are several 

 floating islands, of which C. stellatum forms a large part of the 

 foundation. In the larger lakes about Chicago, such as Wolf and 

 Calumet lakes, the same marginal soil species of moss occur, but 

 so far none has been found floating or submerged in the deeper 

 water. 



Wherever mosses appear, either floating or along the margin 

 of ponds, they aid greatly in the conversion of depressions into 

 land by promoting the advance of other terrestrial plants. There 

 seems to be little difference in the mosses of the pannes and lagoons, 

 except that which can be accounted for by the more shallow water 

 in the former, which may subject the plants to seasonal periods of 

 desiccation, and which would prohibit anything in the way of 

 floating mosses or of floating islands. In both cases it is quite 

 evident that mosses are an important class of plants in the early 

 stages of the pond successions. 



Late stages of pond or lake succession. — Swamp forests. — When 

 comparatively shallow ponds and lakes pass from the aquatic con- 

 ditions, the progress toward the later associations is by growth of 

 vegetation upon the bottom along the margin. Waste material 

 accumulates. In time the open water in the center is entirely 

 eliminated, and a swamp results, which, depending on local con- 

 ditions, may pass into a prairie where mosses take little part, or 

 into a forest where they may be of prime importance. The Thorn- 

 ton and Furnessville swamps are illustrations of the latter type of 

 development in rather early stages, while that at Wilhelm gives a 

 later condition much more mesophytic. The first two are still 

 characterized by depressions and hummocks, which are rarely 

 encountered in the Wilhelm forest. Although humidity, shade, 



