Jennings : A Botanical Survey of Presque Isle. 375 



Eventually with the continued addition of humus to the soil of this 

 zone, there will be built up a belt of deep, semi-liquid muck just inside 

 of the Cephalanthus-Coiiius shrub-zone, and, when this has come to 

 within a {&\v inches of the surface of the water, the Castalia-Nymphcca 

 formation will find the conditions unsuitable to such an extent that it 

 will be supplanted by an association of plants constituting a new for- 

 mation. 



The Decodon-Persicaria Formation. 



The Decodon-Persicaria formation occupies a very distinct zone in 

 some of the Chimney Ponds, in water of a depth from four to twelve 

 inches, but with the older clumps forming mounds above the surface 

 of the water. The soil is always made up of a semi-liquid muck of 

 considerable depth, and represents the abandoned habitat of the Cas- 

 talia-Nxviphcea formation. Pond U has much of this formation, con- 

 stituting a distinct zone, while Pond V is now almost filled with De- 

 codon families and communities, the middle of the pond being in the 

 last stages of the Castalia-Nymphcea formation. The new formation 

 is present sparingly in Ponds T, S, and R, conspicuously so in Z, and 

 forms several strong communities in the west end of Long Pond. 



The typical structure of the formation is as follows : 



Fades. — 



Decodon veriicillatus, Persicaria fluitans. 



Principal Species. — 



Solanuvi dulcamara. 

 Secondary Species. ■ — - 



Naumbergia fhyrsijlora, Cephalanthus occidentaliSy 



Bidens cernua, Scutellaria lateriflora, 



Cicuta bulbifera, , Scirpus cyperinus, 



Alisma plantago-aquatica, Sagittaria latifolia. 



There is a tendency in this formation towards the segregation ot 

 two consocies : the Decodon verticillatus consocies in the shallower 

 water, and the Persicaria consocies in the deeper water. Of the two, 

 however, the former is here much more vigorous, and, where it is best 

 developed, occupies the whole habitat to the exclusion of the latter 

 consocies. 



In other localities these consocies have been regarded as different 

 formations but at Presque Isle their relation is best described as 

 zonation within the same formation. 



