Jennings : A Botanical Survey of Presque Isle. 371 



The Rhiis-Almis Formation. 



The Rhus-Alniis formation is not prominent about Cranberry Pond 

 although around Ridge Pond it is still a strong zone. Around Cran- 

 berry Pond the formation consists almost entirely of the Alnus incana 

 consocies, but where the Aronia-Polytrichum zone is present, the 

 former is absent altogether. In fact, the two formations are apparently 

 coordinate, the Aronia-Polytrichum formation occupying the wider 

 zone of a gently sloping shore, while the Alnus incana consocies oc- 

 cupies the narrower zone of the steeper shores towards the middle and 

 west end of the pond, where the water comes closer to the forest and 

 the zone is more deeply shaded. 



Where the Alnus incana consocies is present, there is no under- 

 growth, except that seedlings and young trees oi Acer saccharinuimx^ 

 more or less numerous. 



The Prunus-Acer Formation. 



Back of the Rhus-Alnus formation and extending to the top of the 

 bank in the habitat of the former Populus-Salix formation, following 

 closely behind the Alnus thicket, is a narrow zone with the following 

 structure : 



Fades. — 



Acer saccharinum, Prnnus serotina. 



Secondary Species. — 



Quercus velulina, Quercus palustris, 



Quercus borealis, Acer rubrutn, 



Sniilax herbacea, Aralia racemosa, 



Phryma leptostachya, Galium aparine, 



Galium circcezans, Osmorhiza clayioni, 



Dryopteris spimilosa. 

 This formation derives many of its species from the adjoining Quercus 

 velutina forest of the Beach-Sand-Plain-Heath -Forest succession but, 

 as the encircling zones advance with the filling up of the lagoon, the 

 habitat comes more and more to occupy a habitat with a black, un- 

 drained, more or less acid soil, and such species as are peculiar to this 

 environment more and more predominate in this formation. With 

 the advent of more shady conditions the Prunus disappears, leaving 

 the zone more typically an Acer saccharinum consocies, but nowhere 

 on the peninsula does this consocies assume any considerable impor- 

 tance. It is usually crowded out by the Quercus velutina formation 



