PUBLIC PARKS OF IOWA 113 



drift prairie stream. Briefly told the Iowa flows through a more or less 

 close walled gorge from Alden to near its junction with South Fork, 

 where it suddenly emerges into a broad valley with a well developed 

 flood plain, and is terraced from Eagle City to the Marshall county line. 

 Its minor tributaries partake of the characters of the parent stream, with 

 this exception, that those from the east have well developed flood plains, 

 relatively low gradients and other characters common to maturely de- 

 veloped streams. It may be of interest to mention that above the forks 

 the Iowa river does not receive a single tributary from the west worthy 

 of a name. The area drained is inconsiderable, drawing almost no 

 tribute save from the north and east. Iowa Geological Survey, Vol. X, An- 

 nual Report 1899, p. 251. 



FOREST FLORA OF HARDIN COUNTY. 

 By L. H. Pammel, Botanist. 



One of the interesting phases of botany is a study of plants with refer- 

 ence of their adaptation. Plants of widely different relationship are fre- 

 quently associated in communities. Such plants show the same adapta- 

 tions as regards their structures and growth. 



Certain 'physiographic features of the country have a marked influence 

 on the plant communities. Sandy, moist rocks support a very different 

 class of plants than limestone rocks, or the alluvial bottoms of the 

 streams. These features often determine the geographic limitations of 

 some trees. The white pine (Pinus strobus) is a very local tree in this 

 state, being confined to the sandstone ledges of eastern and central Iowa. 

 The white pine is not, however, found in this state wherever the sand- 

 stone ledges occur. Extensive carboniferous sandstone deposits occur 

 along the Des Moines from Moingona south, and while the forest growth 

 at various points is somewhat similar to that of Hardin county, three of 

 the prevailing species do not occur, namely, white pine (Pinus strobus) 

 and two birches, the white birch (Betula papyrifera), and the cherry 

 birch (B. lutea). Botanists have long recognized that species tend to 

 move northward or southward, and less frequently plants move eastward 

 and westward. The westward extension of the eastern trees in Iowa is 

 marked by certain valleys. Taking the white pine as an illustration its 

 western limits is marked by the Iowa valley. Dr. S. W. Beyer calls my 

 attention to the report of David Dale Owen,* in which he refers to the 

 occurrence of white pine on the summits of the hills along the Iowa 

 river in Hardin county. Its southern extension is Pine creek in Musca- 

 tine county. The Davenport locality, Reppert Watson and Coulter Gray's 

 Manual (6th Ed.) 49'0, is clearly an error, as I have shown elsewhere. 

 The paper birch, (Betula papyrifera), has its western limit in the same 

 valley, and is clearly more local than the white pine. Macbride reports 

 as follows: "Occurs in cultivation, and is reported abundant along the 

 Boone river east. Perhaps comes within the limits of the county in 

 the northeast corner." Its occurrence there would be extremely interesting, 



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