118 NINTH REPORT. 



quinquefolia, Nabalus altissimus, Cassia marylandica, Physalis heterophylla, 

 Tlviilaria perfoliata, Falcata comosa, Phryma leptostachya, Oxalis stricta, 

 Micrampelis lobata, Prunella vulgaris, Lobelia syphilitica, Irapatiens fulva, 

 Bidens, Mitella, Viola, and others. Interesting also is the large number of 

 sterile ]ilants to be found here. 



The ravine has not escaped human influence. The repeated burning of 

 the slopes near the mouth has strengthened the xerophytic flora. On areas 

 in which denudation of that character has affected the surface, the clearing 

 societies consist of Helianthus divaricatus, Aster kievis, Salix humilis, 8. 

 tristis, Solidago canadensis, S. rigida, Lespedeza frutescens, L. violacea, 

 Lacinaria scariosa, Rhus glabra, Euj)horbia corollata, Viburnum acerfolium 

 on the east side, and of Rhus hirta, Pteris aquilina, Vaccinium vacillans, 

 Apocyniun cannabinum, Monarda fistulosa, Vagnera racemosa, Pimpinella 

 integerrima, Agropyron repens, Andropogon furcatus and others on the west 

 side. This society -is maintained until the seedlings of trees with deeper 

 shade are capable of supporting themselves. Usually Rhus hirta and R. 

 glabra get the ascendency, associated in some places with Corylus ameri- 

 cana and Pteris aquilina. The latter develops best on slopes in such condi- 

 tion, though luxuriant also when near or under the shade of yoimg oak and 

 hickory saplings. As the shrubs and grasses add their share of vegetable de- 

 bris to the soil, making it slowl}^ richer in organic compounds, and the ca- 

 pacity to hold water, heat and oxygen increase, the flora at the lower margin 

 creeps up again. Oaks (Quercus velutina being the most common) and hick- 

 ories soon become dominant, to be followed in arrangement by poplar, bass- 

 wood, elm, maple, and the associated shrubs and herbal undergrowth. Such 

 signs of repeated invasion of mesophytic plant societies are frequent. Even 

 though the changes induced by fires are considerable, as a rule they seem 

 rather to assist in the direction of the original mesophytic association, and 

 to prepare the ground for seeding. 



II. A RAVINE INFLUENCED BY MAN. 



At a distance of about 120 rods (000 m.) to the west, another ravine is sit- 

 uated in this section. Its general direction is more to the north-west, with 

 slopes averaging an incline of 30° to 35°. The conditions of the present 

 association, briefly stated, seem to be these: The slopes, and most of the 

 hill land adjoining the ravine are pasture. This pasture, though extensive, 

 is not natural; it plainly shows that it has been the outcome of various 

 agencies, of which the regular cropping and treading by cattle, and the re- 

 peated fires seem to have been the more active factors. Extensive thickets 

 of Corylus americana and of various species of Crata:'gus, also of Rhus hirta 

 and R. glabra occur here, no doubt the forerunner of an encroaching flora 

 similar to the one in the neighboring ravine. The outposts of the new flora 

 are rapidly advancing, running down the slopes of the ravine from the east. 

 Beneath and about the invading shrubs, the grass-land takes on a some- 

 what different appearance. Extermination iiicreases, as shrubs and depend- 

 ent herbs, species similar to those of the ravine above mentioned, become 

 more and more compact. Several trees (Quercus velutina, Juglans nigra, 

 and Ulmus fulva, with an occasional willow) are standing isolated with de- 

 pendent herbs checked in growth by the grazing cattle, or stunted and sup- 

 pressed because of occasional cultivation. Interesting is the effect of arti- 

 ficial drainage on the habitat of some perennial grasses. The soil is slowly 

 removed by the action of a spring near the upper margin of the ravine. The 



