1905) TRANSEAU—BOGS OF THE HURON RIVER VALLEY 371 
by their leaves and underground stems. The former fall to the 
substratum as they die, but not at the close of each vegetative period. 
Consequently they are soon lost among the sphagnum, and there is 
no distinct annual layer added. 
But beneath this layer of possible aerobic activity, the material 
would seem to be subject to putrefactive agencies. And there can be 
no doubt that such destructive processes are carried on in those situ- 
ations in which the acidity of the soil solution does not preclude 
the existence of the anaerobic bacteria. 
Among the taller shrubs and trees, such as Vaccinium corymbosum, 
Aronia nigra, and Larix laricina, the defoliation takes place each 
autumn. As these plants are of relatively large size, the bulk of the 
material forms a noteworthy annual addition to the substratum. 
When to this is added the twigs and small branches which fall each 
season, we can understand the fact that the substratum is almost 
entirely free of surface water. Usually the ground-water level lies 
y10% below. But the substratum has a high water-capacity and 
's kept constantly moist. Where the sphagnum covering is wanting 
for one reason or another, the dark color of the surface peat shows 
how much more complete is its disintegration as compared with that 
of the other zones. This condition is made possible by its position 
telative to the ground water. On the other hand, as will be shown 
later, the temperature conditions are more favorable in the zones of 
herbaceous and shrubby vegetation. 
ost of the basins in which peat formation is going on actively, 
are subject to considerable variation in water level, both season 
a annual. During the last two years the rainfall has been con- 
‘iderably above the normal in lower Michigan, and many of these bog 
“reas Were flooded. At West Lake, for example, a large part of the 
tamarack area was covered with water to a height of several inches 
i” level of the roots. Most of the basins are also oes 
._. level in the spring and during prolonged sisaaie Y % 
panying such changes there are great differences 1D the rate 
and manner of decay. High water, in so far as it excludes oxygen; 
fa ee 
"ors Putrefaction; if it comes as a result of heavy rains, It eat 
“cidity of the soil solution, increases its oxygen content, an ste 
for a short time favors the growth of the saprophytes causing 
Ik of the 
e : 
“macausis. Low water level exposes a much greater bu 
