370 BOTANICAL GAZETTE : [NOVEMBER 
As to the influence of external factors, high temperatures increase 
the rate of disintegration, while the presence of acids prevents its 
continuance, due to the killing of the bacteria involved. It is to be 
noted that the products of putrefaction, both intermediate and final, 
can be of little use in furnishing food materials for the higher plants. 
With these two processes in mind, we may now consider the 
matter of peat formation as it occurs in this region. We have already 
seen how the substratum is being extended at the edge and renewed 
at the surface by the plants forming the outer zone of the bog vege- 
tation. It consists of sedges, especially forms of Carex and Erio- 
phorum. Each year these plants send up stems and leaves from the 
matted rhizomes. At the approach of winter these are killed, and 
the snow later on aids in bringing them down to the water level. In 
the spring the water covers almost the whole of this zone to the depth 
of several inches. With the gradual lowering of the water level and 
the coming of warmer temperatures, the conditions for eremacausis 
are made favorable. If the water is approximately neutral in its 
chemical reaction, the fungi and bacteria begin the work of disintegra- 
tion, which if continued would result in the complete destruction of 
the vegetable débris. However, on account of the great demand for 
oxygen, the process can be carried on only near the surface of the 
water. Even at a depth of a few centimeters the rate of oxygen 
diffusion is so small, as compared with the demand for it, that pract- 
cally all aerobic bacterial action is prevented. All of the surface — 
which I have examined have been found to be teeming with bactenis 
Close upon the extension of the bog-sedge zone comes t 
sphagnum-heath zone. Here the surface is characterized by os 
lows and elevations, the latter frequently due to the upward gro 
of the sphagnum beneath the shade of the heath plants, but see 
cases due to the building of mounds by ants. In the hollows 
water stands above the substratum throughout a large part of she 
year and even during dry periods lies just at the surface. parent 
sedges, the principal plants of this zone are evergreen. “ 
sphagnum forms a continuous mat of living plants several oe 
meters in thickness, through which all of the oxygem must — 
before it can be available for the eremacausis of the dead . 
material beneath. The cassandra, cranberry, and andre 
compose the bulk of the shrubby vegetation add to the débris 
ES NEA ee nS oe Te 
