IOWA ACADEMY OF SCIENCE 
17 
westerly slopes where they receive the full effects of the “two-o’clock 
sun” and our prevailing* southwesterly summer winds. Sometimes 
where a ridge slopes gradually to the north these openings will follow 
it on that side for some distance, such slopes being but little sheltered 
from both wind and sun. Sometimes other slopes than thofse on thft 
south and west are treeless, but in such cases local topography produce* 
a persistent change in the direction of the air-currents, or the slopes are 
merely a part of a greater dessicated area. 
These limited openings therefore owe their existence to the same causes 
which have produced our broader prairies, and' must be regarded as 
prairie types. 
So great is the difference between the flora of these openings and the 
smaller flora of the surrounding forest, that frequently in the more 
heavily forested sections of the eastern part of the state not a single 
species of either flora is mingled with the other. The difference is evi- 
dently due to the fact that the minor flora of the forest is mesophytic, 
while the prairie flora is essentially xerophytic and can persist in ex- 
posed situations where the former would fail. The writer has made 
extensive detailed comparisons of the flora of various prairie areas,* 
including the prairie openings, and has found the flora practically the 
same. There are variations in the lists of species which may be found 
in the prairie openings of even the same forested regions, but these 
differences are not greater than those which will be ^observed in dif- 
ferent parts of the same larger prairie area of the ordinary type, and 
they take place within the same limits. 
In order that this fact may be brought out more prominently a list 
of the plants which the writer has collected in typical prairie openings 
in the eastern part of the state, chiefly in Johnson county, is here 
included. 
It will be observed that the plants belong without exception to the 
flora of the broader prairies. The relative abundance and distribution 
of the species is also the same. It should be noted that the list includes 
only those species which are now found in the herbarium of the State 
University. For convenience in reference the list is arranged alpha- 
betically. The 7th edition of Gray’s Manual is followed. 
*Por some of the results of these observations see the Bulletin from the Lah. 
of Nat. History, State Univ. of Iowa, Vol. VI, No. 1, and the Report of the Iowa 
Seological Survey, Vol. xx., both published in 1910 (in print at the time of the 
presentation of this paper) . 
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