BIG SPRING PRAIRIE. 11 
A xero-mesophytic area is one in which there is an 
approximately even mixture of the two classes from 
which the name is derived. The same applies to the 
term Hydromesophytic. This enables us to more 
clearly define the peculiar characteristics of limited 
areas, which would otherwise be impossible. 
Furthermore these terms can be employed abso- 
lutely or relatively. Absolutely considered there are 
no extensive xerophytic plant societies in Ohio, as only 
the plants occurring on more or less perpendicular rock 
walls; on edges of cliffs, on the lower and middle 
beaches of Lake Erie; on the nearly perpendicular 
surfaces of freshly eroded river banks can be classed as 
such. Even in these cases the term applies rather to 
the hard condition of life and to the difficulty of gaining 
or maintaining a foothold than to the idea of drought- 
enduring as commonly understood. Relatively we can 
designate that society of any given region, which occurs 
under the most unfavorable conditions, relatively 
xerophytic, and those in the wettest, hydrophytic, and 
the gradations between them as before indicated. As 
the iatter view is apt to lead to confusion, we shall con- 
fine ourselves to the former limitations, and according- 
ly consider the Xero-mesophytic as the extreme of plant 
society in the area under consideration. And even 
under this heading, we can bring only the summits of 
the ridges, the exposed slopes, and the evident outcrops 
of the Niagara limestone. 
Both ridges were formerly densely wooded, but at 
present there are only a considerable number of small 
areas which can be termed woodlands, and even from 
these, the largest and most desirable timber trees have 
been removed. 
Although the ridges as a whole exhibit a character- 
istic forest formation, yet this forest formation can be 
divided into two distinct types occurring respect- 
ively on: 
