32 BOTANICAL GAZETTE [JULY 
the cranberry-sphagnum association immediately behind this 
border vegetation. The last stage of a former large water area 
now occupied by the advancing cranberry-sphagnum association 
is shown in fig. 6. Cranberry and sphagnum build a mat and 
tufts of great compactness and gradually overcome and eliminate 
the swamp loosestrife (Decodon), cat-tail (Typha), Peltandra, and 
others. The advance of the mat out over the surface, even of 
open water, can be demonstrated by a series of such stages and 
Fic. 7.—A sunken mat in the process of rejuvenation; the increased load upon 
the ile of the mat, especially after the heavier tree association became estab- 
lished, caused the sinking of the mat; the cutting of the timber reestablished equilib- 
rium. 
“last vestiges’? indicating the existence of concentric zones of 
Decodon and Typha in quaking mats where formerly water occu- 
pied the area (fig. 4). The mats are floating, for test borings 
through them end abruptly in water which is quite free from 
fibrous material. The space of open water between the upper 
mat and the rest of the deposit below has frequently a depth of 
4-5 feet (1.2-1.5 m.). In several places the peat below such 
mats is fine grained and well decomposed, not at all of a character 
that would indicate a transition structure from the coarsely fibrous 
to the well disintegrated, slightly fibrous deposit resting on the 
coarser mat below. 
