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GOTE TURESSON 
the bog the layer B is, however, of great interest. This amorphous 
deposit of a brownish black color has been laid down in water. By 
some cause or another the bog was flooded and a rich vegetation 
ensued which gave rise to the mud layer in question. The history of 
Lysichiton in the bog goes back to the time of the depositing of this 
layer. When the water subsided, probably while water still re- 
mained in the depression during the wet season, Lysichiton estab- 
lished itself. From our acquaintance with its habitat in ravine pools 
where such mud arises from the decomposition of leaves and other 
organic material swept into the pool, and through our familiarity 
with its abundance on alluvial mud banks, we perceive what a con- 
genial habitat such a deposit would afiford. It is seen from the cross 
section that Lysichiton is rooted in this mud layer. The annual 
decay of great masses of leaves has added to the layer and an ex- 
tensive mud pad has been built up on top of the original deposit. 
The second white moss invasion followed and the soft mass of Sphag- 
num rolled out over the ground occupied by the swamp flora burying 
and suppressing it with the exception of the skunk cabbage which 
was able to hold its own against the oncoming white moss by virtue 
of mere bulkiness. The factors of shade and waste in the formation 
of the skunk cabbage pits have been discussed above, and the figure 
makes clear the structure of these pits. During the rainy reason, 
fall and winter, water collects in the pits, and erosive action loosens 
the Sphagnum layer from the mud pad resulting in a concavity be- 
tween the two strata. 
Thus the conclusion is arrived at that Lysichiton in the Green 
Lake bog is a relict from the swamp flora and not related to the group 
of plants which in recent times have succeeded in entering the bog 
by reason of partial drainage. 
As to the devastation of the forest by Sphagnum indicated in the 
deposit by the Sphagnum stratum (C) overlying the forest bed {D), 
we doubtless evade the difficulties rather than explain them by as- 
suming an alternation of moist and dry periods of great length cor- 
responding to the alternation of strata of Sphagnum and forest in 
the peat bogs as was done by Geikie (12) and Blytt (2) and after 
them by Scottish and Scandinavian botanists in particular. The 
conversion of forest into marsh can take place and be explained with- 
out resorting to such bold conjectures. Nilsson's (17) account of 
the present swamping of the forests in Sweden by Sphagnum is a 
