MICHIGAN ACADEMY OF SCIENCE. 93 



thelypteris, Limnorchis dilatata, Lysias orbiculata, Blephariglottis lacera, 

 Myrica Gale, Gyrostachys cernua, Chiogenes hispidula, etc. 



As the sedges encroach fartlier in on the original lake, the movement for- 

 ward becomes relatively slower, while the filling up increases more rapidly. 

 The zone of the leather-leaved plants gives rise to conditions enabling tama- 

 rack or arbor-vitse, and later spruce, black ash, balsam, white pine and yel- 

 low birch to get a foothold. The swamp northeast of the State Normal at 

 Marquette presents this dryer condition. In more open, wet places, the 

 scattered young Norway and Jack pines and hemlock are usually surrounded 

 by a heavy mat of sphagiuim, bearing upon it almost an entire Cassandra 

 zone, of course on a small scale. In still dryer places the tamarack and as- 

 sociated balsam-fir, black spruce and black ash has an undergrowth consist- 

 ing of dwarf dogwood, xerophytic mosses and various members of the huckle- 

 berry family. 



There are, however, areas where the prevailing bog-societies are not ar- 

 ranged in concentric zones, but parallel. Especially is this the case in areas 

 near the Pioneer Charcoal Blast furnace. The succession is much the same 

 as in lakes and ponds. The sedge zone grades into a Cassandra zone asso- 

 ciated with Spirsea salicifolia and alder, which in turn is followed by a tama- 

 rack, black spruce and balsam fir society with an undergrowth consisting of 

 a thick carpet of Sphagnum, pitcher plants, snowberry, Labrador tea and 

 others. 



With the change of conditions in the environment — largely produced by 

 the plants themselves — a change in the plant societies inevitably follows. 

 The flora is succeeded by a society adapted to the new conditions, which 

 will in time become replaced by other forms. The societies are usually dom- 

 inated by species which are among the first to invade new areas, thus illus- 

 trating the importance of the historical as well as the biological factors. 

 However, these suggestions are far from illustrating concretely the complex 

 agencies involved and the manner in which they are related to produce the 

 particular conditions or environment. The life history of swamps is not al- 

 ways the same, and neither are the factors similar or even easily recognized. 

 Closer observation reveals an extraordinary network of relations that binds 

 every society in its place and endows it with the character it possesses. For 

 a fuller analysis and a more detailed account the reader is referred to the 

 forthcoming paper of Dr. Davis on "The formation, character and distribu- 

 tion of peat bogs in the Northern Peninsula of Michigan " and the literature 

 cited there. 



Sand Areas. — On account of the intermediate relation which it bears to 

 the swamps on the one hand, and the rocky hills on the other, the flora of 

 sand-areas will be considered next. Plains of sand, partly terraces and fossil 

 beaches, partly sandy drift, are frequent. The flora is interesting though 

 rather monotonous, and limited both in individuals and species. In the 

 well-marked sand area west of Ridge Street the soil, recently disturbed by 

 man, is a bare sand, in nature like that of the dunes near the lake. In var- 

 ious places portions of the underlying rock crop out like islands. The vege- 

 tation consists largely of pioneer plants such as the common weeds and of 

 Hypericum Canadense, Anaphalis margaritacea and Leptilon Canadense; 

 in depressions containing slightly more moisture are found Carex tenuis, C. 

 tribuloides Bebbii, Juncus effusus, J. tenuis, Scirpus cyperinus and Euthamia 

 graminifolia. Near "Sugar Loaf Mountain," northwest of Marquette, and 

 in other places, the sandy plains are covered with a dense growth of Vaccin- 

 iums yielding a great abundance of fruit. It would be difficult to find 



