76 
IOWA ACADEMY OP SCIENCES. 
Ammannia coccinea Rottb. Not common. Reported only 
from Story county. 
Veronica anagallis L. Not common. 
Juncus nodosus L., var. megacephalus Torr. Not rare. 
BecJcmannia erucceformis Host,, var. unijlora Scrib. Quite 
common near two of the pools, but not found by the author at 
any other point. It is also reported from Story (introduced) 
and Plymouth counties. 
As has been noted, the plants which constitute this flora are 
for the most part inhabitants of dry and more or less barren 
regions. The flora may be duplicated in part in several barren 
isolated spots in other portions of the state. One of these is 
found in Muscatine county, and many of its interesting forms 
have already been reported by Mr. Fred Reppert; another is 
in Dubuque county; and still others are mentioned by Prof. L. 
H. Pammel.* 
It is probably the remnant of a flora which once covered the 
greater part of the north half of the state. It is closer in its 
relation to the western than to the eastern flora, and its evolu- 
tion probably took place to the west and southwest beyond the 
limits of the glacial sheet. 
The recession of the glaciers left a barren surface, for the 
most part covered with sand and boulders, and seamed and 
scarred by the vast sea of ice. The depressions were occupied 
by water, and upon the bleak hills this flora slowly established 
itself. But its own presence gradually caused an accumulation 
of finer surface soil, and other plants, more vigorous and rapid 
growers, took possession of the now fertile spots. The fertile 
area thus increased until only a remnant of the original flora 
was left in the few spots which presented conditions most nearly 
like those which prevailed soon after the disappearance of the 
ice sheet. 
The distribution of the lichen flora probably differed from 
that of the higher plants. The wonderful vitality of the lichens, 
especially as illustrated by their habits far to the north, admits 
of the belief that they were able to exist even through the 
glacial period. It is probable that the ledges of the Sioux 
quartzite, then much more prominent, were covered with lichens 
even before the glacial epoch, and that the same force which 
ground out the boulders from the solid rock carried fragments 
of lichens out over the state eastward and southward. It is 
*Proc. Iowa Acad. Sci., vol. Ill, p. 106. 
