520 Part IV. Chapter 3. 
running through the sand prairies the encroachment of the forest has been 
slow. The first tree-growth that invades the sand prairies is a xerophytic as- 
sociation composed mainly of the black-jack oak Ouercus marylandica and 
usually known as black-jack timber. Besides the oak, which constitutes about 
so per cent of the forest, there is about 35 per cent of the black oak. 
Onercus tinctoria (= Q. velutina) and ı5 percent of the hickory Carya 
odorata (= Hicoria microcarpa). The trees seldom exceed a foot in diameter, and 
they are generally very crooked, gnarled and full of dead branches. The 
hickory is nearly always sterile, only the largest trees producing fruit. 
The undergrowth, according to C. A. Hart and H. A. GLEASoN?), consists of young trees 
of the above species and Rhus aromatica, Amorpha canescens and Salix tristis. In the edge of 
the woods prairie bunch grasses occur while in the denser shade of the trees are found 
Panicum cognatum, Triodia cuprea (= Tricuspis seslerioides), Eragrostis trichodes (= E. tenuis), 
Paspalum setaceum and Andropogon furcatus, all these grasses in bunches few and wide apart. 
The remainder of the flora is ee = Irre een and Tephrosia virginiana, which 
is extremely abundant and gro ten feet or more in diameter together with 
Opuntia humifusa (O. er ae a ee: Cassia chamaecrista, Froelichia 
campestris, Helianthus oceidentalis, Helianthemum majus. The soil in which the trees and herbs 
ow is a pure sand and the formation of leaf mold goes on very slowly. With the first traces 
of leaf mold there appear Aquilegia canadensis, u stellata, Anemone virginiana, Agrimonia 
mollis and later as the soil deepens are found Smilacina (Vagnera) racemosa, Eupatorium agera- 
toides, Geum canadense and Asclepias Si with ehr trees of Cercis canadensis, Morus 
ru d Celtis oceidentalis. 
Oak Grove Formation. In eastern Iowa and elsewhere the oak groves 
are remarkable for the paucity of large trees, but wherever they occur, their 
composition varies. Sometimes one species predominates and sometimes 
another, . so that they receive the distinctive names of white oak, bur oak, or 
so called black oak groves. For example one grove consisted of Quercus 
coccinea which predominated with Ouercus rubra and O. macrocarpa, Q. alba 
as subordinate species, and occasionally Q. Muhlenbergü (= O. acuminala) 
and ©. finctoria. In southern Iowa ©. marylandica becomes the dominant 
tree and elsewhere O. rinoides, O. obtusiloba (= O. minor) the ‘post oak, 
which occurs sparingly in the southern groves?). In Wisconsin) the oak 
openings consist of Ouercus alba, O. rubra, 0. coccinea, Juglans cinerea, 
Corylus americana with such herbs beneath as Anemone nemorosa, Lupinus 
perennis, Baptisia leucophaca, Monarda fistulosa, while such herbs, as Linaria 
canadensis, Oenothera rhombipetala, Aster multiflorus, A. oblongifolius, Arcto- 
staphylos uva-ursi, Castilleia sessiliflora are transitional between the oa 
openings and the undulating prairie above the Wisconsin River. 
This formation in Oklahoma and Texas corresponds to the open savanna forests of the 
Cross Timbers described as a prolongation of the deciduous forest into Texas. With much pro- 
ı) Bulletin Illinois State Laboratory of Natural History VII: 171— 178. January 1907- 
2) FirzPATRIck, T. J. and M. F. L.: The native oak Groves of Iowa. Plant Fa IV: 
69. April 1901. 
3) LuEDERS, HERMAN F.: The Vegetation of the Town Prairie du Sac. Transactions Wisconsin 
Academy Sciences, Arts and Letters X (1894 -95): 510 
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