60 



land forest on the other hand, is well wooded and shaded, and much 

 more humid. The substation also has a considerable amount of litter, 

 leaves, and humus. This region may be considered as transitional be- 

 tween the upland and lowland forest, but it represents, not one but two 

 transitional stages, the south slope approaching the upland forest type, 

 and the southeast slope approaching that of the lowland forest. 

 Thus, if one walked from the upland forest down the slope of the 

 south ravine, and eastward to the southeast valley slope to the bottom- 

 land forest, he would traverse all the main degrees of conditions found 

 at Station IV. 



The forest cover consists primarily of the following trees : white 

 oak (Quercus alba), black oak (Q. velutina), walnut (Juglans nigra), 

 pignut (Carya glabra), and, in smaller numbers, mulberry (Morns 

 rubra), red oak (Quercus rubra), shag-bark hickory (Carya ovata), 

 bitternut (C. cordiformis) ; and of the following shrubs : redbud (Cer- 

 cis canadensis), sassafras (Sassafras varii folium), moonseed (Menis- 

 permum canadense), five-leaved ivy (Psedera quiiiquefolia), grape 

 (Vitis cinerea), prickly ash (Zanthoxylum americanum), and sumac 

 (Rhus glabra), the latter growing in large colonies on the open south 

 ravine-slope. On the more moist and shaded southeast slope lived the 

 clearweed (Pilea pumila), a plant quite characteristic of moist deep- 

 shaded woods. Thus sumac and clearweed may be considered as in- 

 dex plants to the physical conditions in different parts of these two 

 slopes, one shaded and the other rather open. 



The atmometer, located on the upper part of the south ravine slope, 

 gave a relative humidity of 31 per cent, of the standard in the garden 

 of the Normal School. It will be recalled that in the upland forest 

 (Station IV, a) the atmometer gave 54 per cent., the comparison 

 showing how much less the evaporating power of the air is on the 

 south ravine slope than it is in the upland forest. The relative evap- 

 oration was not determined for the southeast slopes, but the presence 

 of Pilea clearly indicates that it is less than on the south ravine slope, 

 where the instrument was located. On the lower parts of the valley 

 slope, where this substation grades into the lowland, the layers of dead 

 matted leaves and humus reached to a considerable depth, and looked 

 as if they had been pressed down by drifting snows. Such places were 

 found to contain very few- animals. 



This habitat is characterized by a sloping surface, by relative open- 

 ness on the ravine side and dense shade on the valley slope, by rela- 

 tively humid air, by second-growth forest somewhat transitional be- 

 tween that of the uplands (Station IV, a) and the river bottoms (Sta- 

 tion IV, c), by a relatively large amount of shrubbery, by considerable 



