BIG SPRING PRAIRIE. 83 
seeds find such ready lodgment upon this bare soil, and 
the conditions seem to be suitable for their germina- 
tion, especially upon the banks sloping to the south. 
Here there is a proper amount of light and heat in 
connection with the ever-present moisture in this muck 
soil. Along some few of the ditches, willows are the 
predominent trees or shrubs. Maples occur only occa- 
sionally. 
Most of the trees figured on Map II, originated 
along ditches, and an inspection will show that elms 
and poplars are the abundant species. 
On the Peter Brayton farm in Big Spring Town- 
ship, Seneca County, there occurs a peculiar group of 
trees along one of the ditches. This group comprises 
several maples ranging from 18 inches to 30 inches in 
diameter, a few elms, a couple of oaks, a black haw, an 
ash, a dogwood, and several willows of 14 to 15 inches 
in diameter. 
TREES ON BURNED AREAS. 
Prairie fires have been frequently assigned as the 
cause of prairies and the absence of trees upon them; but 
on Big Spring Prairie, fires are the direct cause of the 
encroachment of thickets and forests upon it. Ifa 
prairie fire burns simply the tops of the dead grasses, but 
does not distroy the sod and roots, ordinary weeds make 
but little headway in gaining foothold. Schimper 
gives, as the cause of the density of sod, the fact that 
grasses propagate abuntly by vegetative reproduc- 
tion, and adds that this very density of grass rootstocks 
and roots with their great capacity for the absorption 
of soil moisture is one of the chief hindrances to the 
germination of the seeds of trees and to the flourishing 
of tree seedlings. Herbaceous plants, not including 
grasses, can not engage incontest against woody plants. 
Qn an area on which sod and soil are burned, 
mosses and a few annual herbs make their appearance 
