378 Annals of the Carnegie Museum. 



Quercus pahisiris, Quercus rubra, 



Acer saccharinum, Salix nigra, 



Toxicodendron pubescens. Viburnum opulus, 



Psedera quinquefolia, Galium circczzaiis, 



Gaiium triflorum, Unifoliuni canadense, 



Plu-yma leptostachya, Inipatiens biflora, 



Ilex verticillata, Boehmeria cylindrica, 



Smilax herhacea, Salomonia biflora, 



Onoclea sensibilis, Osmunda claytoniana, 



Osniunda spectabilis, Osmorhiza claytoni, 



Trillium e rectum. 



Vegetation other than trees is not a prominent feature of this forest. 

 Many of the herbaceous and shrubby species enumerated above occur 

 only sparingly and are really constituents of another formation. 



The total area covered by the formation is not large. In the vicin- 

 ity of the Chimney Ponds it is confined to irregular zones around the 

 borders of the basins. There is, however, marking the position of 

 extinct ponds, a circular area of this formation about 30 rods in diam- 

 eter south of the west end of Long Pond and another smaller one to 

 the northeast of Big Chimney Pond, R, near the bay. 



The ecological conditions obtaining in the habitat of the Ulmus- 

 Acer formation at Presque Isle are closely similar in most respects to 

 those obtaining about numerous fiUed-in basins throughout the 

 ' southern part of the glaciated area of the northern states. There is 

 always the black muck-soil, imperfectly drained, more or less acid, 

 and with a high water content, the position being more or less 

 sheltered by neighboring banks. At a higher elevation, or farther 

 north, the normal formation in such a habitat is the Tamarack forest, 

 or, later, the Arbor Vit;e forest.^' It is not probable that the Ulmus- 

 Acer formation represents the climax forest for these pond basins, but 

 that, with the annual accumulation of considerable quantities of forest 

 litter, much of which at Presque Isle blows into it during the fall and 

 winter from the more open and exposed Quercus velutina formation, 

 the soil will finally become higher and more xerophytic to such an 

 extent that the Quercus velutina formation will be able to invade and 

 eventually occupy the habitat. Even under present conditions there 



**' Whitford, H. N. "The Genetic Development of the Forests of Northern 

 Michigan." Bot. Gaz., 31 : 312-316, May, 1901. 



