34 The Vegetation of tue 



across a brook; ponds were formed, the trees died when such that could 

 not exist in water; afterwards, when the beaver was gone, by and by the 

 dam broke, the water flew off and grasses formed a meadow. Such forest 

 meadows may sooner or later turn again into forest and have nothing in 

 common with the true prairies. 



In the upper Mississippi district forest and prairie struggled for ex- 

 istence before culture ended that struggle by subdoing both to the plow. 

 Now the trees are planted on the cultivated prairie land, and so, although 

 regardlessly wasted even in localities fit only for tree growth, the forest 

 got the advantage over the prairie. But even before, when forest and 

 prairie were in their natural state, the trees gained ground at the cost of 

 the prairies. When we examine the constituent parts of the western 

 woods, we find that they gradually diminishing in species follow the large 

 river vallies and even along the small tributaries; then we conclude that 

 all those species from their eastern home traveled westward. The fittest 

 to travel and to settle: the cottonwood, the sycamore and the hackberry, 

 the elm spread the farthest towards the Rocky Mountains, others not 

 farther than Missouri and Iowa, or did not pass over the Mississippi. Not 

 the woods, as was believed, yielded to the prairie, but, on the contrary, the 

 prairie yielded to the woods. 



When in the course of time the wide level plain was furrowed by 

 streaming water, from year to year hollowed banks sank down, deep val- 

 lies were formed, flanked with steep bluffs once the banks of the rivers, 

 then sod and argillaceous underground and humus thoroughly mixed, as 

 to-day by the plow on the prairie, formed a soil fit to receive the spreading 

 forest growth, and species after species could migrate to the far west. 



As the woody plants did westward, so the prairie plants wandered east- 

 ward, diminishing by and by in number. Of 55 species of the prairie- 

 flora, that under the same latitude doi\'t go beyond the AUeghanies, 23 do 

 not reach the State of Ohio, and Iowa has many western species that east- 

 ward do not cross the Mississippi. 



We distinguish wet and dry prairie. The former in the river bottoms 

 or in depressions of the dry prairies which occupy the high and undulating 

 plain. 



The number of species of our prairie plants is scarcely more than 200, 

 and many of them are not restricted to the prairie. The first in spring 

 blooming on the dry prairie are: Draba caroliniana, xinemone decapetala, 

 Ranunculus fascicularis, Oxalis violacea, Androsace occidentalis. Then 

 follow in May, Lithospernum angustifolium,* canescens and hirtum, Trox- 

 imon cuspidatum, Baptisia leucophsea, Pentstemon pubesceus: in June, 

 Viola delphinifolia, Scutellaria parvula, Linum sulcatum, Polygala incar- 

 nata and sanguinea, Asclepias Meadii and obtusifolia, Sisyrinchium Bermu- 

 diana, Tradescantia virginica, Cirsium pumilum, Silene Antirrhrina, 



*Lithosperinuin longiflorum Sprang, is the same as L. angustifolium Mich, and 

 was founded on specimens with earlier and larger flowers. 



