FLORISTIC FEATURES OF A PRAIRIE PROVINCE 383 



other on the sides of which are Ulmus americana, Gleditschia tri- 

 acanthos, Salix aiid Rhus glabra, among which Poa pratensis and 

 Andropogon scoparius grow. Beginning- in the next glen and 

 extending sparsely across tlie hillside to the established wood are 

 seen Ulmus americana, Populus deltoides, Fraxinus viridis, Acer 

 negnndo, Pyrus ioivensis, Gleditschia triacanthos, one tree of 

 Quercus macrocarpa, one of Q. rubra and one of Acer nigrum. 

 The ground herbage is bine grass, ruderaJs, Andropogon scop- 

 arius and Artemesia ludoviciana, which illustrates the overlap- 

 ing of associations. Fraxinus, Acer and Quercus are final trees 

 of the terminal forest of this region. 



Fig. 157. — Pyrus lowensis. A tree of the pioneer forest. 



T'hese preliminary trees are youngest, most remote from the 

 wood. There are seedlings beneath them. They are seen in the 

 order from the pioneer to the well-known type of the mature 

 forest. There are no stumps or signs of decay in these prelim- 

 inary clusters. Prairie grasses grow under the first stand of trees 

 which are close enough together to cause much shade. These 

 ere in the adjacent established wood replaced by blue grass, wood 

 ruderals and some typical wood plants, among the more con- 

 spicuous of which are heart leaved Viola palmata, while the dis- 

 sected leaved Viola pedatifida occurs just outside on the prairie 

 on moist slopes and V. pedata on slope and ridges. These indi- 

 cations show that forest is here encroaching upon the prairie. 



