146 BOTANICAL GAZETTE | MARCH 
that these structures are due to the difficult absorption in peaty 
soil, the humus acids and the lack of oxygen being detrimental 
to normal root activities. For similar reasons the normal soil 
activities of bacteria and fungi are lessened, and as a result of 
this relative lack of decay great quantities of peat accumulate. 
All of these peculiarities of peat bogs may be referred to the 
lack of drainage, since the stagnant conditions prevent oxidation 
and the removal of the humus acids. The lack of drainage is of 
course due to topographic conditions. Peat bogs and undrained 
lakes, therefore, are features of a young topography, since several 
agencies combine to cause their rapid destruction. Rivers may 
work back and tap the undrained lakes or inlets may fill them up. 
Probably the most important agent in the death of undrained 
lakes, however, is the vegetation, as will be seen later. The 
great abundance of lakes and ponds in the young glaciated 
regions as compared with older regions to the south is a striking 
proof of their short life. 
In the immediate neighborhood of Chicago typical peat bogs 
are scarce. They find their best development in the depressions 
of the dune region, where they may be called abundant. Wher- 
ever a sag between two dunes is low enough to retain moisture 
for the greater part of the season, the conditions favor the 
development of an undrained swamp flora. If the depression is 
so low that the water level outcrops throughout the year, then 
there is an undrained pond or lake. The first flora in this latter 
case consists of plants that are able to exist with little or no 
change in the water of the pond except through rain and evap- 
oration. Among these plants the alga Chara takes a promi- 
nent place. The water lilies (Nymphaea and Nuphar) are an 
exceedingly important constituent of this first vegetation, as is 
also Utricularia, which is represented by several species. The 
above species, together with others, play a great part in filling 
up lakes, since their remains accumulate with almost no decay. 
Chara in particular is a soil former of great importance. The 
rapidity with which these filling processes are carried on is 
striking; in pools of known age among the rubbish heaps of 
