HARSHBERGER : PHYTO-GEOGRAPHIC SKETCH 143 
grated north from the denser forest that clothed the valleys and 
slopes of the southern Allegheny mountains. 
The dominant trees of the forest that covered and still covers 
in patches southeastern Pennsylvania is composed of the following 
species: Tulip-poplar, Liviodendron Tulipifera 1..; chestnut, Cas- 
tanea dentata (Marsh.) Borkh. (Castanea sativa Americana Gray); 
black walnut, Juglans nigra L.; red oak, Quercus rubra L.; white 
oak, Q. alba L.; scarlet oak, Q. coccinea Wang.; chestnut oak, Q. 
Prines L.; Spanish oak, Q. digitata (Marsh.) Sudw. (Q. falcata 
Michx.); beech, Fagus Americana Sweet (F. ferruginea Ait.); 
ficoria ovata (Mill.) Britton (Carya alba Nutt.); hackberry, Ce/tis 
occidentalis L..; butternut, Juglans cinerea L.; sweet gum, Liguid- 
ambar Styraciflua L.; persimmon, Diospyros Virginiana L.; white 
elm, Ulmus Americana L.; white ash, Fraxinus Americana L.; 
wild red cherry, Prunus Pennsylvanica Lf; pignut, Hicoria glabra 
(Mill.) Britton (Carya porcina Nutt.); silver maple, Acer sacchari- 
num L. (Acer dasycarpum Ehrh.); sugar maple, Acer saccharum 
Marsh. (Acer saccharinum WWang.); red maple, Acer rubrum L., 
buttonwood, Platanus occidentalis L.; small-fruited hickory, Hicoria 
microcarpa (Nutt.) Britton (Carya microcarpa Nutt.); and iron- 
wood, Ostrya Virginiana (Mill.) Willd. These trees are found 
Ona great variety of soils, but reach their greatest size on the 
dry alluvial soils of the creek and river bottoms. Thus the 
black walnut, tulip-poplar, white elm, buttonwood, red maple 
and silver maple reach their best development on such soils. The 
white oak, white ash, chestnut, etc., seem to grow equally well in 
the drier upland soils. The red cedar, Juniperus Virginiana L., 
On the other hand, seems to be confined to barren places and to 
rocky outcrops, while the trees that grow along the banks of the 
Streams within the region comprise the red maple, Acer rubrum L.; 
the hornbeam, Carpinus Caroliniana Walt.; swamp oak, Quercus 
palustris DuRoi; buttonwood, Platanus occidentalis L.; box-elder, 
Acer Negundo L. (Negundo aceroides Moench); beech, Fagus Amer- 
tcana Sweet ; Sassafras Sassafras (L.) Karst. (S. officinale Nees), 
and several birches and willows. 
These trees form a dense canopy, and shade the forest floor, 
So that the secondary species, shrubs, sapling trees and herbs, 
Must be tolerant of such dense shade. The dominant trees 
