544 Part IV. Chapter 3. 
. deep woods. Ampelopsis (Parthenocissus) quinquefolia, Vitis vulpina, Rhus radicans grow at the 
forest edge, Menispermum canadense, Sicyos angulatus, Clematis virginiana, Echinocystis lobata 
also oecur. — The secondary layer of shrubs and small trees is never well developed in this 
formation. Two climbers oecur Apios tuberosa, Clematis Pitcheri and the following grasses scat- 
tered in patches: Cinna arundinacea, Asprella (Hystrix) hystrix. 
The lower herbaceous layer in spring is characterized’ by Phlox divaricata, Erythronium 
albidum, E. americanum, Viola scabriuscula, Aquilegia canadensis (on steep bluffs), Cypripedium 
pubescens (rare), Orchis spectabilis (rare), Claytonia virginica, Dicentra cucullaria, D. canadensis, 
Sanguinaria canadensis and Caulophyllum thalictroides haunting secluded dells are rarely seen in 
the woods. The estival-serotinal aspect is heterogeneous, consisting of Sanicula marylandica, Cryp- 
totaenia canadensis, Osmorrhiza longistylis, Geum canadense, Acalypha virginica. Parietaria 
pennsylvanica, Cystopteris fragilis, Adiantum pedatum also occur. 
The Bur oak-Elm-Walnut Association has much in common with 
the preceding into which it grades. It is characterized by the disappearance 
of both Ouercus rubra and Carya alba, which are replaced chiefly by facies 
of bur oak Ouercus macrocarpa and elm Ulmus americana, in which the 
walnut Juglans nigra is often abundant. A large number of eastern trees 
have likewise dropped out, viz: Aesculus glabra, Amelanchier canadensis, 
 Asimina, Betula nigra, Cercis, Crataegus mollis and Staphylea trifolia. In 
places especially on steep overhanging bluffs along the Missouri occur Funi- 
Perus virginiana, Tilia americana, Ostrya virginiana, Zanthoxylum americanum. 
Along the bluffs grow Shepherdia argentea, Prunus demissa, Amelanchier 
botryapium. 
An interesting modification of this association is found on the coteaus of 
eastern Dakota (Plateau du Coteau du Missouri) extending into Canada. 
Acer saccharum has found a lodgement in some of the canyons on the eastern 
margin of the coteaus and with Oxereus macrocarpa, Ulmus americana, Tilia, 
Ostrya forms a characteristic forest. The common shrubs are Corylus ameri- 
cana, Rosa sp., Prunus virginiana and americana. The trees of this distriet 
are crooked, gnarled, low and spreading, in fact it is a brush thicket. The 
undershrub layer and the climbers of the two forest associations considered are 
practically the same, although certin of the eastern species of shrubs and herbs 
have entirely disappeared. 
Pine Ridge and Pine Bluff Formation. This formation is characterized by 
a single facies Pinus ponderosa var. scopulorum. Open woodland of this 
species occur on exposed bluffs, ridges etc. Under such conditions, the indi- 
viduals are medium-sized. The trees are dotted here and there in the thin 
grassy vegetation. In some places trees of Funiperus virgimiana are intermin- 
gled. In the pine forest secondary species are absent, although such herbs a 
Pirola chlorantha, P. secunda, Pterospora andromedea are exceptions. 
Lower down the pine is intermingled with Fraxinus viridis, Ostrya virginiana, Celtis 0C- 
o 
cidentalis, Ulmus americana, Populus monilifera, Salix amygdaloides and the montane species Acer 
glabrum, Populus tremuloides, Betula oceidentalis with a shrubby layer of Prunus demissa, 
Amelanchier alnifolia, Sheperdia argentea, Rosa Fendleri, Ribes oxyacanthoides, R. cereum, R. 
aureum, R. floridum, Vitis vulpina and Rhus radicans, R. trilobata with Symphoricarpos paueiflorus, 
S,. occidentalis and the vine Ampelopsis (Parthenoeissus) quinquefolia. The herbs of especial 
Hese 
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