MICHIGAN ACADEMY OF SCIENCE. 95 



are frequeiith' found to prevail, namely, rock-ridges without much soil, sup- 

 porting a xerophytic flora, and depressions, with moist and deeper 'soil sup- 

 porting either a mesophytic, or, as in some places, a swamp flora. 



The succession on rock undoubtedly began with the lichens in an order 

 such as this: First the crustaceous, then the foliaceous lichens, and finally 

 such forms as Cladonia rangiferina, C. pulchella, Stereocaulon paschali, 

 together Avith Selaginella rupestris and various xerophytic mosses. A large 

 lichen (Umbellicaria), invariably is found covering with its black thalloid 

 frond the bare surfaces, forming a striking feature. Fastened firmly to the 

 rock by holdfasts, it dries up and curls up between rains but remains un- 

 injured until the next shower freshens it up again. Of the ferns frequenting 

 these exposed dry places, the most common are Pohq:)odium vulgare, Phegop- 

 teris drj'opteris, Woodsia ilvensis, and often also Dryopetris fragrans. The 

 variety of rock vegetation is very noticeable — lichen societies adjoining 

 small dejDressions containing a miniature swamp flora, or bordering groups 

 of pines, young broadleaved trees, or crevices with a shrubby vegetation. 

 AVithout the aid of the physical and chemical process of weathering, and in 

 spite of the poverty of the soil, the presence of humus and an abundance of 

 atmospheric moisture enable these plants to succeed. Their existence here, 

 however, is only a very transient one. The C|uartzite shows almost no dis- 

 integration, but with the more or less complete decay of the granite and dolo- 

 mite, these various societies disappear, having done their share in establish- 

 ing a soil to support a tree vegetation. 



From an ecological point of view, the region has reached a relatively fairly 

 mature stage in various places. Perhaps it is because of marked influences 

 due to the proximity of the great lakes that mixed pine and almost pure 

 deciduous forests are found upon hills and in valleys which would otherwise 

 support only a xerophytic society. That the soil factor is of an ec^ually im- 

 portant influence need not be reiterated. The clay soils of the southern 

 slope of Mount IMesnard with their dense and luxuriant growth of deciduous 

 trees are especially an example of this kind. 



The devastating influence of man is not to be disregarded, since by far the 

 greater number of localities studied show unmistakable signs of artificial 

 conditions — clearing, produced both by the cutting and burning of timber. It 

 is needless to describe the drear}^ ancl repellent sight which a deserted lumber 

 region of thousands of dead ancl blackened pines presents. The consequent 

 greater insolation permits only a few plants to thrive in arid, xerophytic con- 

 ditions like these. Most numerously represented are usually those species 

 found in the immediate neighborhood, wliich have the lightest seed or a colored 

 fruit, and are rapid growers. Epilobium angustifolium, Erigeron Canadensis, 

 various goldenrods and especially the blackberries spring up everywhere, 

 forming a tangled thicket, giving the clearing the well-known *' fire- weed" 

 aspect. A few scattering poplars, white birches and wild reel cherries soon 

 appear, overtop the fireweed, gradually shade them out, and maintain them- 

 selves until the pines crowd them out, or until the deeper shade conditions 

 enable the maples, basswoods and red oaks to establish themselves. 



Rivei's and Lakes. — The sections studied near the "Electric Light and 

 Power House"- — about four miles northwest of Marquette, ancl those near 

 Prescjue Isle, may be considered representative of iieaclwater and of flood- 

 plain conditions of Dead River. At the section first mentioned the stream is 

 shallow, cold and swift-flowing, with a bottom composed of bed rock and 

 gravel. Within the stream there is practically no vegetation. On the banks, 

 however, the pines and deciduous trees of the bordering hills extend down 



