144 
Ohio Biological Survey 
Forest openings indieated in the elearing successions .—Very near to 
a tract of forest — within about fifty feet (probably the effective limit of 
seed distribution)—saplings are much more numerous than at greater 
distances. This growth is composed of the same species as are found 
in the neighboring woodland, and is often so close, as to almost exclude 
meadow vegetation. But openings are found in this, and each contains a 
rich meadow flora. These will grow smaller as the trees increase in size, 
and the quantity of meadow vegetation, and probably also the number 
of species, will decrease. It is such spots as these which probably form 
the openings in the upland forests. 
It is likely that the original upland forests grew up in a manner veri¬ 
similar to that now shown in clearings. Natural meadows do not occur 
in this region, and the only meadow plants, outside of clearings, are found 
in the small openings in the forests. The history of such spots is proba¬ 
bly that outlined above. Conditions are still favorable to the development 
of extensive meadows, if the forest is removed. Then the plants, which 
still maintain a foothold in the openings, will spread rapidly and cover the 
cleared area, only to be slowly restricted again by the growth of new 
forests. 
III. SLOPE SERIES 
The slopes of the region naturally fall into two principal divisions, 
ravine slopes, and major valley slopes or river bluffs. That such a sepa¬ 
ration of slopes should be made, may at first sight seem strange. In fol¬ 
lowing a growing ravine from its source to its entrance into one of the 
larger streams crossing the region, a connected history is involved. Such 
a stream is, in physiography, termed susequent. But here the sequence 
may stop. The large valley is not always older than the small one. The 
Ohio and lower Miami rivers did not in preglacial times follow their 
present course. Because of the drainage changes shown in the accom¬ 
panying map, hg. i8, parts of the Ohio and Miami valleys exhibit marks 
of extreme youth. And youth in a large valley does not impose the same 
conditions upon vegetation, that youth in a ravine does. The narrow and 
deep ravine is quite different from the xerophytic bluff (Cowles, 1901 ,a). 
The history of the river valley is not the history of its tributary valley. 
The river series of Cowles (1901), including the ravine, the river 
bluff, and the flood plain, is somewhat comparable to the slope series and 
the flood plain series of the present paper. But here, the river bluff and 
the flood plain are such prominent and important features of the tbpo- 
