1905] TRANSEAUBOGS 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 V actinium 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 

 5-10 cm below. But the substratum has a high water- capacity and 

 is 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 

 relative 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. 



Most of the basins in which peat formation is going on actively, 

 are subject to considerable variation in water levfl, both seasonal 

 and annual. During the last two years the rainfall has been con- 

 siderably above the normal in lower Michigan, and many of these bog 

 areas were flooded. At West Lake, for example, a large part of the 

 tamarack area was covered with water to a height of several inches 

 above the level of the roots. Most of the basins are also subject to 

 higher water level in the spring and during prolonged rainy periods. 

 Accompanying such changes there are great differences in the rate 

 and manner of decay. High water, in so far as it excludes oxygen, 

 favors putrefaction ; if it comes as a result of heavy rains, it decreases 

 the acidity of the soil solution, increases its oxygen content, and at 

 least for a short time favors the growth of the saprophytes causing 

 eremacausis. Low water level exposes a much greater bulk of the 



