FLORA OF MICHIGAN. 19 



ing south of latitude 40, is all within the limits generally assigned to 

 severe glacial action. Second, its mountains trend east and west, from the 

 Pyrenees to the Carpathians and the Caucasus beyond, near its southern 

 border; and they had glaciers of their own, which must have begun opera- 

 tions, and poured down the northward flanks, while the plains were still 

 covered with forest on the retreat from the great ice wave coming from the 

 north. Attacked both on front and rear, much of the forest must have 

 perished then and there. Third, across the line of retreat of those which 

 may have flanked the mountain ranges, or were stationed south of them, 

 stretched the Mediterranean, an impassable barrier." 



" Greenland may be referred to, by way of comparison, as a country 

 which, having undergone extreme glaciation, bears the marks of it in the 

 extreme poverty of its flora, and in the absence of the plants to which its 

 southern portion, extending six degrees below the arctic circle, might be 

 entitled. It ought to have trees, and might support them. But since 

 destruction by glaciation, no way has been open for their return." 



" In the American continent -the mountains run north and south. The 

 trees, when touched on the north by the on-coming refrigeration, had only 

 to move their southern border southward, along an open way, and there 

 was no impediment to their due return. So our lines have been cast in 

 pleasant places, and the goodly heritage of forest trees is one of the 

 consequences. ' ' 



A 



FLORA OF THE JACK-PINE PLAINS. 



The plants of this region are all found in one or more of the regions 

 previously enumerated. 



The soil of these plains is mainly sand of considerable depth which dries 

 out quickly after a rain, and is then especially liable to be burned over, 

 the burning often destroying every living plant above the surface of the 

 soil. In this way, by repeated burning, much of the vegetable matter is 

 removed, leaving the surface soil thin. 



The following seventy species of plants are almost certain to be found 

 in considerable quantity on any extended area of Jack-pine plains: 



a. THOSE MOST COMMON. 



Amelanchier Canadensis, var. oblongifolia, Torr. & Gray. Dwarf June-Berry. 



Andropogon fureatus, Muhl. Finger, or Beard-Grass. 



Andropogon scoparius, Michx. Beard-Grass. 



Arctostaphylos Uva-ursi, Spreng. Bearberry. 



Aster Icevis, L. Aster. 



Carex Pennsylvania, Lam. Pennsylvania Sedge. 



Danthonia spicata, Beauv. Wild Oat-Grass. 



Epigc&a repens, L. Trailing Arbutus. 



Erigeron Canadensis, L. Horse-weed. 



Gaultheria procumbens, L. Wintergreen. 



Myrica asplenifolia, Endl. Sweet Fern. 



Oryzopsis Canadensis, Torr. Mountain Rice. 



Pinus Bariksiana, Lambert. Scrub, or Jack-pine. 



Populus tremuloides, Michx. Aspen. 



Prunus Pennsylvania, L. f. Wild Red, or Pin Cherry, 



Prunus pumila, L. Sand Cherry. 



Prunus Virginiana, L. Choke- Cherry. 



Pteris aquilina, L. Brake. Eagle Fern. 



Quercus coccinea, Wang. Scarlet Oak. 



Quercus tinctoria, Bartr. Black Oak. 



Rumex Acetosella, L. Sheep Sorrel. 



3 



