952 BATTLES OF PLANTS IN THE WORLD 
by the size and age of the vegetation, as well as by its 
difference in character. 
Many of the peat bogs were once small ponds or 
lakes. The peat moss and other plants which find shal- 
low water a congenial place to grow in begin march- 
ing out from the edge of the water toward the centre 
of the pond. The stems of the peat die below and 
grow above. So in this way they build up a floor or 
platform in the water. The dead peat now in the 
water below does not thoroughly rot, as the leaves do 
in the moist ground of the forest, because the water 
shuts out the air. The partly dead stems of the moss 
pile up quite fast in making the platform, which some- 
times is entirely composed of peat. Other plants may 
grow along with the peat. Their dead bodies also help 
to build up this floor beneath. 
The army of peat and other water plants contimues 
to march out toward the centre of the pond, though 
slowly. Finally, in many cases the line around the 
shore meets in the centre and the pond is filled up, the 
floor having been extended entirely across. But they 
keep on adding each year to the floor, raising it higher 
and higher, until it is high enough and dry enough for 
the marching armies of the dry land grasses, shrubs, 
and trees. At length a wood comes to stand on the 
floor built across the pond by the peat moss and the 
other members of its society. 
