136 IOWA ACADEMY OF SCIENCES. 



an abundant fern, forming great masses, and with it, in 

 the small draws, Osmunda Claytoniana, and Adiantum 

 pedaturn. 



The richest field for ferns is to be found in the lower 

 sandstone outcrops. These are low, rounded greatly 

 eroded hills, and here and there, as along Pine creek in 

 Minnesota and the Tamarack swamp, contain the white 

 pine {Pinus Strobus). On these benches, richly laden with 

 moisture from the region beyond, the greatest number of 

 Pteridophytes occur. In the Pine creek region, such 

 species as Phegopteris polypodioides, Phegopteria Drt/opteris 

 PdUea gracilis, Woodsia ohttisa, Pohjpodiuni vulgare, Aspid- 

 ium spinulosum, var intermedium and Lijcopodiiim lucidulum 

 occur. In the Tamarack region, similar in all respects, an 

 additional species occurs on the exposed sandstone rocks, 

 namely, Woodsia Hvensis. The basis of the sandstone 

 rocks, close to the rivers and marshes have such species as 

 Osmunda cinnamoniea, Osmunda regalis, -diid Osmunda, i latj- 

 tonia. The marshes contain Aspidium Thelypteris and 

 Onoclea sensihilis. The Selaginella rupestris is an inhab- 

 itant of sandy barrens and dry sandstone rocks. The 

 Camptosorus rhizophgllus along the Mississippi occurs on 

 detached limestone rocks, close to the flood-phiin. 



It is only necessary, in this connection, to make a brief 

 reference to the general features of ferns in central Iowa. 

 The Cij stopfer is frag His is the most widely distributed fern, 

 found in rich woods. The Adiantum pedaturn also occurs 

 in rich woods, but they are more moist; the Asplenium 

 Felix-fcemina in upland, moist, rich woods, or in small 

 gullies; the Onoclea in similar places, but rare. The Poly- 

 podium vulgare, Woodsia ohtusa and Camptosorus rhizophyllus 

 are found on sandstone ledges; Onoclea sensibilis in wet 

 meadows, near springs. It is found in the vicinity of Steam- 

 boat Rock, in moist ground, with Juniperus communis and 

 Cypripedium spectahile. 



The Carboniferous sandstone along the Iowa river, in 

 the vicinity of Steamboat Rock, contains such a remark- 

 able instance of northern plants, that a few w^ords regard- 

 ing them will not be amiss. The white pine {Pinus Strobus), 



