14 IOWA STUDIES IN NATURAL HISTORY 
ature conditions under which they thrive best. The columns 
showing extreme mean temperatures may likewise be taken as 
giving the limits beyond which these forms do not successfully 
maintain themselves. 
FLORAL CHARACTERISTICS 
In general, the floral characteristics of this county fall into 
two large classes, forest and prairie. In its original undisturbed 
condition a band of timber extended along the main water 
courses and was very generally distributed over the roughest of 
the land to each side.* The remainder of the county was prai- 
rie. In the bottom land, the native timber was chiefly elm, mixed 
with cotton-wood, birch, willow, ete., while on the upland and 
the rough land, even when quite near the streams, the forest was 
composed primarily of oak, frequently mixed with hickory and 
often found in conjunction with hazelnut, particularly if the 
oak be scattered. 
The relation of the forested areas to the rough land may be 
seen by comparing the topographical map (Plate II) with the 
several township maps which indicate the present distribution of 
timber. From this it will be at once deduced that the rough 
land only, at any distance from the larger streams, provides 
eonditions favorable for the maintenance of forest. From this 
it is at once seen that the present forested areas are only in the 
rougher parts of the county, namely the rocky bluffs along the 
Iowa River north of Iowa City, all of Newport township, the 
south half of Big Grove, Jefferson, and Monroe townships, and 
parts of Graham and Cedar townships. In addition to these, the 
most important strips of timber le along the valleys of Clear 
Creek and Old Man’s Creek with scattered areas throughout 
Washington, Sharon, and Liberty townships. It is a significant 
fact that the distribution of trees along the creek valleys just 
noted is mainly on the south and more abrupt slope of the valley 
in each case. In other words, native trees, and hence forest, have 
been able to establish and maintain themselves only on those 
areas on which they were afforded protection from evaporating 
forces. This bears out Professor Shimek’s conclusions{ regard- 
*B. Shimek, from certain unpublished data. 
+The Prairies, B. Shimek; page 230. 
